chore: remove dead code

This is intended to fail at present: it just adds a test case containing
a minimization of a Mathlib slowdown from #3807.

Prior to #3807, the declaration `exists_algHom_adjoin_of_splits'''` at
the end of the file would take around 16,000 heartbeats. Now it takes
around 210,000 heartbeats.

---------

Co-authored-by: Leonardo de Moura <leomoura@amazon.com>

.github/workflows/check-prelude.yml

@@ -0,0 +1,26 @@
+name: Check for modules that should use `prelude`
+
+on: [pull_request]
+
+jobs:
+  check-prelude:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          # the default is to use a virtual merge commit between the PR and master: just use the PR
+          ref: ${{ github.event.pull_request.head.sha }}
+          sparse-checkout: src/Lean
+      - name: Check Prelude
+        run: |
+          failed_files=""
+          while IFS= read -r -d '' file; do
+            if ! grep -q "^prelude$" "$file"; then
+              failed_files="$failed_files$file\n"
+            fi
+          done < <(find src/Lean -name '*.lean' -print0)
+          if [ -n "$failed_files" ]; then
+            echo -e "The following files should use 'prelude':\n$failed_files"
+            exit 1
+          fi

.github/workflows/ci.yml

@@ -62,7 +62,7 @@ jobs:
                 "os": "ubuntu-latest",
                 "release": false,
                 "quick": false,
-                "shell": "nix-shell --arg pkgsDist \"import (fetchTarball \\\"channel:nixos-19.03\\\") {{}}\" --run \"bash -euxo pipefail {0}\"",
+                "shell": "nix develop .#oldGlibc -c bash -euxo pipefail {0}",
                 "llvm-url": "https://github.com/leanprover/lean-llvm/releases/download/15.0.1/lean-llvm-x86_64-linux-gnu.tar.zst",
                 "prepare-llvm": "../script/prepare-llvm-linux.sh lean-llvm*",
                 "binary-check": "ldd -v",
@@ -76,7 +76,7 @@ jobs:
                 "os": "ubuntu-latest",
                 "release": true,
                 "quick": true,
-                "shell": "nix-shell --arg pkgsDist \"import (fetchTarball \\\"channel:nixos-19.03\\\") {{}}\" --run \"bash -euxo pipefail {0}\"",
+                "shell": "nix develop .#oldGlibc -c bash -euxo pipefail {0}",
                 "llvm-url": "https://github.com/leanprover/lean-llvm/releases/download/15.0.1/lean-llvm-x86_64-linux-gnu.tar.zst",
                 "prepare-llvm": "../script/prepare-llvm-linux.sh lean-llvm*",
                 "binary-check": "ldd -v",
@@ -98,7 +98,8 @@ jobs:
                 // exclude seriously slow tests
                 "CTEST_OPTIONS": "-E 'interactivetest|leanpkgtest|laketest|benchtest'"
               },
-              {
+              // TODO: suddenly started failing in CI
+              /*{
                 "name": "Linux fsanitize",
                 "os": "ubuntu-latest",
                 "quick": false,
@@ -106,7 +107,7 @@ jobs:
                 "CMAKE_OPTIONS": "-DLEAN_EXTRA_CXX_FLAGS=-fsanitize=address,undefined -DLEANC_EXTRA_FLAGS='-fsanitize=address,undefined -fsanitize-link-c++-runtime' -DSMALL_ALLOCATOR=OFF -DBSYMBOLIC=OFF",
                 // exclude seriously slow/problematic tests (laketests crash)
                 "CTEST_OPTIONS": "-E 'interactivetest|leanpkgtest|laketest|benchtest'"
-              },
+              },*/
               {
                 "name": "macOS",
                 "os": "macos-latest",
@@ -153,7 +154,7 @@ jobs:
                 "quick": false,
                 "cross": true,
                 "cross_target": "aarch64-unknown-linux-gnu",
-                "shell": "nix-shell --arg pkgsDist \"import (fetchTarball \\\"channel:nixos-19.03\\\") {{ localSystem.config = \\\"aarch64-unknown-linux-gnu\\\"; }}\" --run \"bash -euxo pipefail {0}\"",
+                "shell": "nix develop .#oldGlibcAArch -c bash -euxo pipefail {0}",
                 "llvm-url": "https://github.com/leanprover/lean-llvm/releases/download/15.0.1/lean-llvm-x86_64-linux-gnu.tar.zst https://github.com/leanprover/lean-llvm/releases/download/15.0.1/lean-llvm-aarch64-linux-gnu.tar.zst",
                 "prepare-llvm": "../script/prepare-llvm-linux.sh lean-llvm-aarch64-* lean-llvm-x86_64-*"
               },
@@ -251,7 +252,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     defaults:
       run:
-        shell: ${{ matrix.shell || 'nix-shell --run "bash -euxo pipefail {0}"' }}
+        shell: ${{ matrix.shell || 'nix develop -c bash -euxo pipefail {0}' }}
     name: ${{ matrix.name }}
     env:
       # must be inside workspace
@@ -382,8 +383,14 @@ jobs:
           cd build/stage1
           ulimit -c unlimited # coredumps
           # exclude nonreproducible test
-          ctest -j4 --output-on-failure ${{ matrix.CTEST_OPTIONS }} < /dev/null
+          ctest -j4 --progress --output-junit test-results.xml --output-on-failure ${{ matrix.CTEST_OPTIONS }} < /dev/null
         if: (matrix.wasm || !matrix.cross) && needs.configure.outputs.quick == 'false'
+      - name: Test Summary
+        uses: test-summary/action@v2
+        with:
+          paths: build/stage1/test-results.xml
+        # prefix `if` above with `always` so it's run even if tests failed
+        if: always() && (matrix.wasm || !matrix.cross) && needs.configure.outputs.quick == 'false'
       - name: Check Test Binary
         run: ${{ matrix.binary-check }} tests/compiler/534.lean.out
         if: ${{ !matrix.cross && needs.configure.outputs.quick == 'false' }}
@@ -410,7 +417,8 @@ jobs:
         run: |
           cd build
           ulimit -c unlimited # coredumps
-          make update-stage0 && make -j4
+          # clean rebuild in case of Makefile changes
+          make update-stage0 && rm -rf ./stage* && make -j4
         if: matrix.name == 'Linux' && needs.configure.outputs.quick == 'false'
       - name: CCache stats
         run: ccache -s
@@ -421,19 +429,21 @@ jobs:
             progbin="$(file $c | sed "s/.*execfn: '\([^']*\)'.*/\1/")"
             echo bt | $GDB/bin/gdb -q $progbin $c || true
           done
-      - name: Upload coredumps
-        uses: actions/upload-artifact@v3
-        if: ${{ failure() && matrix.os == 'ubuntu-latest' }}
-        with:
-          name: coredumps-${{ matrix.name }}
-          path: |
-            ./coredumps
-            ./build/stage0/bin/lean
-            ./build/stage0/lib/lean/libleanshared.so
-            ./build/stage1/bin/lean
-            ./build/stage1/lib/lean/libleanshared.so
-            ./build/stage2/bin/lean
-            ./build/stage2/lib/lean/libleanshared.so
+      # has not been used in a long while, would need to be adapted to new
+      # shared libs
+      #- name: Upload coredumps
+      #  uses: actions/upload-artifact@v3
+      #  if: ${{ failure() && matrix.os == 'ubuntu-latest' }}
+      #  with:
+      #    name: coredumps-${{ matrix.name }}
+      #    path: |
+      #      ./coredumps
+      #      ./build/stage0/bin/lean
+      #      ./build/stage0/lib/lean/libleanshared.so
+      #      ./build/stage1/bin/lean
+      #      ./build/stage1/lib/lean/libleanshared.so
+      #      ./build/stage2/bin/lean
+      #      ./build/stage2/lib/lean/libleanshared.so
 
   # This job collects results from all the matrix jobs
   # This can be made the “required” job, instead of listing each
@@ -442,9 +452,10 @@ jobs:
     name: Build matrix complete
     runs-on: ubuntu-latest
     needs: build
-    if: ${{ always() }}
+    # mark as merely cancelled not failed if builds are cancelled
+    if: ${{ !cancelled() }}
     steps:
-    - if: contains(needs.*.result, 'failure') ||  contains(needs.*.result, 'cancelled')
+    - if: contains(needs.*.result, 'failure')
       uses: actions/github-script@v7
       with:
         script: |

.github/workflows/copyright-header.yml

@@ -0,0 +1,20 @@
+name: Check for copyright header
+
+on: [pull_request]
+
+jobs:
+  check-lean-files:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Verify .lean files start with a copyright header.
+      run: |
+        FILES=$(find ./src -type d \( -path "./src/lake/examples" -o -path "./src/lake/tests" \) -prune -o -type f -name "*.lean" -exec perl -ne 'BEGIN { $/ = undef; } print "$ARGV\n" if !m{\A/-\nCopyright}; exit;' {} \;)
+        if [ -n "$FILES" ]; then
+          echo "Found .lean files which do not have a copyright header:"
+          echo "$FILES"
+          exit 1
+        else
+          echo "All copyright headers present."
+        fi

.github/workflows/nix-ci.yml

@@ -6,6 +6,7 @@ on:
     tags:
       - '*'
   pull_request:
+    types: [opened, synchronize, reopened, labeled]
   merge_group:
 
 concurrency:
@@ -71,18 +72,18 @@ jobs:
         run: |
           sudo chown -R root:nixbld /nix/var/cache
           sudo chmod -R 770 /nix/var/cache
-      - name: Install Cachix
-        uses: cachix/cachix-action@v12
-        with:
-          name: lean4
-          authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
-          skipPush: true  # we push specific outputs only
       - name: Build
         run: |
           nix build $NIX_BUILD_ARGS .#cacheRoots -o push-build
       - name: Test
         run: |
-          nix build $NIX_BUILD_ARGS .#test -o push-test
+          nix build --keep-failed $NIX_BUILD_ARGS .#test -o push-test || (ln -s /tmp/nix-build-*/source/src/build/ ./push-test; false)
+      - name: Test Summary
+        uses: test-summary/action@v2
+        with:
+          paths: push-test/test-results.xml
+        if: always()
+        continue-on-error: true
       - name: Build manual
         run: |
           nix build $NIX_BUILD_ARGS --update-input lean --no-write-lock-file ./doc#{lean-mdbook,leanInk,alectryon,test,inked} -o push-doc
@@ -98,9 +99,6 @@ jobs:
           # gmplib.org consistently times out from GH actions
           # the GitHub token is to avoid rate limiting
           args: --base './dist' --no-progress --github-token ${{ secrets.GITHUB_TOKEN }} --exclude 'gmplib.org' './dist/**/*.html'
-      - name: Push to Cachix
-        run: |
-          [ -z "${{ secrets.CACHIX_AUTH_TOKEN }}" ] || cachix push -j4 lean4 ./push-* || true
       - name: Rebuild Nix Store Cache
         run: |
           rm -rf nix-store-cache || true

.github/workflows/pr-release.yml

@@ -126,21 +126,19 @@ jobs:
           if [ "$NIGHTLY_SHA" = "$MERGE_BASE_SHA" ]; then
             echo "The merge base of this PR coincides with the nightly release"
 
-            MATHLIB_REMOTE_TAGS="$(git ls-remote https://github.com/leanprover-community/mathlib4.git nightly-testing-"$MOST_RECENT_NIGHTLY")"
-
-            if [[ -n "$MATHLIB_REMOTE_TAGS" ]]; then
-              echo "... and Mathlib has a 'nightly-testing-$MOST_RECENT_NIGHTLY' tag."
-              MESSAGE=""
-            else
-              echo "... but Mathlib does not yet have a 'nightly-testing-$MOST_RECENT_NIGHTLY' tag."
-              MESSAGE="- ❗ Mathlib CI can not be attempted yet, as the \`nightly-testing-$MOST_RECENT_NIGHTLY\` tag does not exist there yet. We will retry when you push more commits. If you rebase your branch onto \`nightly-with-mathlib\`, Mathlib CI should run now."
-            fi
-
             STD_REMOTE_TAGS="$(git ls-remote https://github.com/leanprover/std4.git nightly-testing-"$MOST_RECENT_NIGHTLY")"
+            MATHLIB_REMOTE_TAGS="$(git ls-remote https://github.com/leanprover-community/mathlib4.git nightly-testing-"$MOST_RECENT_NIGHTLY")"
 
             if [[ -n "$STD_REMOTE_TAGS" ]]; then
               echo "... and Std has a 'nightly-testing-$MOST_RECENT_NIGHTLY' tag."
               MESSAGE=""
+
+              if [[ -n "$MATHLIB_REMOTE_TAGS" ]]; then
+                echo "... and Mathlib has a 'nightly-testing-$MOST_RECENT_NIGHTLY' tag."    
+              else
+                echo "... but Mathlib does not yet have a 'nightly-testing-$MOST_RECENT_NIGHTLY' tag."
+                MESSAGE="- ❗ Mathlib CI can not be attempted yet, as the \`nightly-testing-$MOST_RECENT_NIGHTLY\` tag does not exist there yet. We will retry when you push more commits. If you rebase your branch onto \`nightly-with-mathlib\`, Mathlib CI should run now."
+              fi
             else
               echo "... but Std does not yet have a 'nightly-testing-$MOST_RECENT_NIGHTLY' tag."
               MESSAGE="- ❗ Std CI can not be attempted yet, as the \`nightly-testing-$MOST_RECENT_NIGHTLY\` tag does not exist there yet. We will retry when you push more commits. If you rebase your branch onto \`nightly-with-mathlib\`, Std CI should run now."
@@ -151,7 +149,9 @@ jobs:
             echo "but 'git merge-base origin/master HEAD' reported: $MERGE_BASE_SHA"
             git -C lean4.git log -10 origin/master
 
-            MESSAGE="- ❗ Std/Mathlib CI will not be attempted unless your PR branches off the \`nightly-with-mathlib\` branch."
+            git -C lean4.git fetch origin nightly-with-mathlib 
+            NIGHTLY_WITH_MATHLIB_SHA="$(git -C lean4.git rev-parse "origin/nightly-with-mathlib")"
+            MESSAGE="- ❗ Std/Mathlib CI will not be attempted unless your PR branches off the \`nightly-with-mathlib\` branch. Try \`git rebase $MERGE_BASE_SHA --onto $NIGHTLY_WITH_MATHLIB_SHA\`."
           fi
 
           if [[ -n "$MESSAGE" ]]; then

.github/workflows/update-stage0.yml

@@ -40,18 +40,32 @@ jobs:
       run: |
           git config --global user.name "Lean stage0 autoupdater"
           git config --global user.email "<>"
-    - if: env.should_update_stage0 == 'yes'
-      uses: DeterminateSystems/nix-installer-action@main
     # Would be nice, but does not work yet:
     # https://github.com/DeterminateSystems/magic-nix-cache/issues/39
     # This action does not run that often and building runs in a few minutes, so ok for now
     #- if: env.should_update_stage0 == 'yes'
     #  uses: DeterminateSystems/magic-nix-cache-action@v2
     - if: env.should_update_stage0 == 'yes'
-      name: Install Cachix
-      uses: cachix/cachix-action@v12
+      name: Restore Build Cache
+      uses: actions/cache/restore@v3
       with:
-        name: lean4
+        path: nix-store-cache
+        key: Nix Linux-nix-store-cache-${{ github.sha }}
+        # fall back to (latest) previous cache
+        restore-keys: |
+          Nix Linux-nix-store-cache
+    - if: env.should_update_stage0 == 'yes'
+      name: Further Set Up Nix Cache
+      shell: bash -euxo pipefail {0}
+      run: |
+        # Nix seems to mutate the cache, so make a copy
+        cp -r nix-store-cache nix-store-cache-copy || true
+    - if: env.should_update_stage0 == 'yes'
+      name: Install Nix
+      uses: DeterminateSystems/nix-installer-action@main
+      with:
+        extra-conf: |
+          substituters = file://${{ github.workspace }}/nix-store-cache-copy?priority=10&trusted=true https://cache.nixos.org  
     - if: env.should_update_stage0 == 'yes'
       run: nix run .#update-stage0-commit
     - if: env.should_update_stage0 == 'yes'

CMakeLists.txt

@@ -78,6 +78,10 @@ add_custom_target(update-stage0
   COMMAND $(MAKE) -C stage1 update-stage0
   DEPENDS stage1)
 
+add_custom_target(update-stage0-commit
+  COMMAND $(MAKE) -C stage1 update-stage0-commit
+  DEPENDS stage1)
+
 add_custom_target(test
   COMMAND $(MAKE) -C stage1 test
   DEPENDS stage1)

CODEOWNERS

@@ -6,7 +6,6 @@
 
 /.github/ @Kha @semorrison
 /RELEASES.md @semorrison
-/src/ @leodemoura @Kha
 /src/Init/IO.lean @joehendrix
 /src/kernel/ @leodemoura
 /src/lake/ @tydeu
@@ -14,9 +13,31 @@
 /src/Lean/Data/Lsp/ @mhuisi
 /src/Lean/Elab/Deriving/ @semorrison
 /src/Lean/Elab/Tactic/ @semorrison
+/src/Lean/Language/ @Kha
 /src/Lean/Meta/Tactic/ @leodemoura
 /src/Lean/Parser/ @Kha
 /src/Lean/PrettyPrinter/ @Kha
+/src/Lean/PrettyPrinter/Delaborator/ @kmill
 /src/Lean/Server/ @mhuisi
 /src/Lean/Widget/ @Vtec234
 /src/runtime/io.cpp @joehendrix
+/src/Lean/Elab/Tactic/RCases.lean @digama0
+/src/Init/RCases.lean @digama0
+/src/Lean/Elab/Tactic/Ext.lean @digama0
+/src/Init/Ext.lean @digama0
+/src/Lean/Elab/Tactic/Simpa.lean @digama0
+/src/Lean/Elab/Tactic/NormCast.lean @digama0
+/src/Lean/Meta/Tactic/NormCast.lean @digama0
+/src/Lean/Meta/Tactic/TryThis.lean @digama0
+/src/Lean/Elab/Tactic/SimpTrace.lean @digama0
+/src/Lean/Elab/Tactic/NoMatch.lean @digama0
+/src/Lean/Elab/Tactic/ShowTerm.lean @digama0
+/src/Lean/Elab/Tactic/Repeat.lean @digama0
+/src/Lean/Meta/Tactic/Repeat.lean @digama0
+/src/Lean/Meta/CoeAttr.lean @digama0
+/src/Lean/Elab/GuardMsgs.lean @digama0
+/src/Lean/Elab/Tactic/Guard.lean @digama0
+/src/Init/Guard.lean @digama0
+/src/Lean/Server/CodeActions/ @digama0
+/src/Init/Data/Array/Subarray.lean @david-christiansen
+

RELEASES.md

@@ -8,74 +8,393 @@ This file contains work-in-progress notes for the upcoming release, as well as p
 Please check the [releases](https://github.com/leanprover/lean4/releases) page for the current status
 of each version.
 
-v4.7.0 (development in progress)
+v4.8.0 (development in progress)
 ---------
 
+* **Executables configured with `supportInterpreter := true` on Windows should now be run via `lake exe` to function properly.**
+
+  The way Lean is built on Windows has changed (see PR [#3601](https://github.com/leanprover/lean4/pull/3601)). As a result, Lake now dynamically links executables with `supportInterpreter := true` on Windows to `libleanshared.dll` and `libInit_shared.dll`. Therefore, such executables will not run unless those shared libraries are co-located with the executables or part of `PATH`. Running the executable via `lake exe` will ensure these libraries are part of `PATH`.
+
+  In a related change, the signature of the `nativeFacets` Lake configuration options has changed from a static `Array` to a function `(shouldExport : Bool) → Array`. See its docstring or Lake's [README](src/lake/README.md) for further details on the changed option.
+
+* Lean now generates an error if the type of a theorem is **not** a proposition.
+
+* Importing two different files containing proofs of the same theorem is no longer considered an error. This feature is particularly useful for theorems that are automatically generated on demand (e.g., equational theorems).
+
+* Functional induction principles.
+
+  Derived from the definition of a (possibly mutually) recursive function, a **functional induction principle** is created that is tailored to proofs about that function.
+
+  For example from:
+  ```
+  def ackermann : Nat → Nat → Nat
+    | 0, m => m + 1
+    | n+1, 0 => ackermann n 1
+    | n+1, m+1 => ackermann n (ackermann (n + 1) m)
+  ```
+  we get
+  ```
+  ackermann.induct (motive : Nat → Nat → Prop) (case1 : ∀ (m : Nat), motive 0 m)
+    (case2 : ∀ (n : Nat), motive n 1 → motive (Nat.succ n) 0)
+    (case3 : ∀ (n m : Nat), motive (n + 1) m → motive n (ackermann (n + 1) m) → motive (Nat.succ n) (Nat.succ m))
+    (x x : Nat) : motive x x
+  ```
+
+  It can be used in the `induction` tactic using the `using` syntax:
+  ```
+  induction n, m using ackermann.induct
+  ```
+
+* The termination checker now recognizes more recursion patterns without an
+  explicit `termination_by`. In particular the idiom of counting up to an upper
+  bound, as in
+  ```
+  def Array.sum (arr : Array Nat) (i acc : Nat) : Nat :=
+    if _ : i < arr.size then
+      Array.sum arr (i+1) (acc + arr[i])
+    else
+      acc
+  ```
+  is recognized without having to say `termination_by arr.size - i`.
+
+* Shorter instances names. There is a new algorithm for generating names for anonymous instances.
+  Across Std and Mathlib, the median ratio between lengths of new names and of old names is about 72%.
+  With the old algorithm, the longest name was 1660 characters, and now the longest name is 202 characters.
+  The new algorithm's 95th percentile name length is 67 characters, versus 278 for the old algorithm.
+  While the new algorithm produces names that are 1.2% less unique,
+  it avoids cross-project collisions by adding a module-based suffix
+  when it does not refer to declarations from the same "project" (modules that share the same root).
+  PR [#3089](https://github.com/leanprover/lean4/pull/3089).
+
+* Attribute `@[pp_using_anonymous_constructor]` to make structures pretty print like `⟨x, y, z⟩`
+  rather than `{a := x, b := y, c := z}`.
+  This attribute is applied to `Sigma`, `PSigma`, `PProd`, `Subtype`, `And`, and `Fin`.
+
+* Now structure instances pretty print with parent structures' fields inlined.
+  That is, if `B` extends `A`, then `{ toA := { x := 1 }, y := 2 }` now pretty prints as `{ x := 1, y := 2 }`.
+  Setting option `pp.structureInstances.flatten` to false turns this off.
+
+* Option `pp.structureProjections` is renamed to `pp.fieldNotation`, and there is now a suboption `pp.fieldNotation.generalized`
+  to enable pretty printing function applications using generalized field notation (defaults to true).
+  Field notation can be disabled on a function-by-function basis using the `@[pp_nodot]` attribute.
+
+* Added options `pp.mvars` (default: true) and `pp.mvars.withType` (default: false).
+  When `pp.mvars` is false, metavariables pretty print as `?_`,
+  and when `pp.mvars.withType` is true, metavariables pretty print with a type ascription.
+  These can be set when using `#guard_msgs` to make tests not rely on the unique ids assigned to anonymous metavariables.
+  [#3798](https://github.com/leanprover/lean4/pull/3798).
+
+* Added `@[induction_eliminator]` and `@[cases_eliminator]` attributes to be able to define custom eliminators
+  for the `induction` and `cases` tactics, replacing the `@[eliminator]` attribute.
+  Gives custom eliminators for `Nat` so that `induction` and `cases` put goal states into terms of `0` and `n + 1`
+  rather than `Nat.zero` and `Nat.succ n`.
+  Added option `tactic.customEliminators` to control whether to use custom eliminators.
+  Added a hack for `rcases`/`rintro`/`obtain` to use the custom eliminator for `Nat`.
+  [#3629](https://github.com/leanprover/lean4/pull/3629),
+  [#3655](https://github.com/leanprover/lean4/pull/3655), and
+  [#3747](https://github.com/leanprover/lean4/pull/3747).
+
+* The `#guard_msgs` command now has options to change whitespace normalization and sensitivity to message ordering.
+  For example, `#guard_msgs (whitespace := lax) in cmd` collapses whitespace before checking messages,
+  and `#guard_msgs (ordering := sorted) in cmd` sorts the messages in lexicographic order before checking.
+  PR [#3883](https://github.com/leanprover/lean4/pull/3883).
+
+* The `#guard_msgs` command now supports showing a diff between the expected and actual outputs. This feature is currently
+  disabled by default, but can be enabled with `set_option guard_msgs.diff true`. Depending on user feedback, this option
+  may default to `true` in a future version of Lean.
+
+Breaking changes:
+
+* Automatically generated equational theorems are now named using suffix `.eq_<idx>` instead of `._eq_<idx>`, and `.def` instead of `._unfold`. Example:
+```
+def fact : Nat → Nat
+  | 0 => 1
+  | n+1 => (n+1) * fact n
+
+theorem ex : fact 0 = 1 := by unfold fact; decide
+
+#check fact.eq_1
+-- fact.eq_1 : fact 0 = 1
+
+#check fact.eq_2
+-- fact.eq_2 (n : Nat) : fact (Nat.succ n) = (n + 1) * fact n
+
+#check fact.def
+/-
+fact.def :
+  ∀ (x : Nat),
+    fact x =
+      match x with
+      | 0 => 1
+      | Nat.succ n => (n + 1) * fact n
+-/
+```
+
+* The coercion from `String` to `Name` was removed. Previously, it was `Name.mkSimple`, which does not separate strings at dots, but experience showed that this is not always the desired coercion. For the previous behavior, manually insert a call to `Name.mkSimple`.
+
+* The `Subarray` fields `as`, `h₁` and `h₂` have been renamed to `array`, `start_le_stop`, and `stop_le_array_size`, respectively. This more closely follows standard Lean conventions. Deprecated aliases for the field projections were added; these will be removed in a future release.
+
+* The change to the instance name algorithm (described above) can break projects that made use of the auto-generated names.
+
+* `Option.toMonad` has been renamed to `Option.getM` and the unneeded `[Monad m]` instance argument has been removed.
+
+v4.7.0
+---------
+
+* `simp` and `rw` now use instance arguments found by unification,
+  rather than always resynthesizing. For backwards compatibility, the original behaviour is
+  available via `set_option tactic.skipAssignedInstances false`.
+  [#3507](https://github.com/leanprover/lean4/pull/3507) and
+  [#3509](https://github.com/leanprover/lean4/pull/3509).
+
+* When the `pp.proofs` is false, now omitted proofs use `⋯` rather than `_`,
+  which gives a more helpful error message when copied from the Infoview.
+  The `pp.proofs.threshold` option lets small proofs always be pretty printed.
+  [#3241](https://github.com/leanprover/lean4/pull/3241).
+
+* `pp.proofs.withType` is now set to false by default to reduce noise in the info view.
+
+* The pretty printer for applications now handles the case of over-application itself when applying app unexpanders.
+  In particular, the ``| `($_ $a $b $xs*) => `(($a + $b) $xs*)`` case of an `app_unexpander` is no longer necessary.
+  [#3495](https://github.com/leanprover/lean4/pull/3495).
+
+* New `simp` (and `dsimp`) configuration option: `zetaDelta`. It is `false` by default.
+  The `zeta` option is still `true` by default, but their meaning has changed.
+  - When `zeta := true`, `simp` and `dsimp` reduce terms of the form
+    `let x := val; e[x]` into `e[val]`.
+  - When `zetaDelta := true`, `simp` and `dsimp` will expand let-variables in
+    the context. For example, suppose the context contains `x := val`. Then,
+    any occurrence of `x` is replaced with `val`.
+
+  See [issue #2682](https://github.com/leanprover/lean4/pull/2682) for additional details. Here are some examples:
+  ```
+  example (h : z = 9) : let x := 5; let y := 4; x + y = z := by
+    intro x
+    simp
+    /-
+    New goal:
+    h : z = 9; x := 5 |- x + 4 = z
+    -/
+    rw [h]
+
+  example (h : z = 9) : let x := 5; let y := 4; x + y = z := by
+    intro x
+    -- Using both `zeta` and `zetaDelta`.
+    simp (config := { zetaDelta := true })
+    /-
+    New goal:
+    h : z = 9; x := 5 |- 9 = z
+    -/
+    rw [h]
+
+  example (h : z = 9) : let x := 5; let y := 4; x + y = z := by
+    intro x
+    simp [x] -- asks `simp` to unfold `x`
+    /-
+    New goal:
+    h : z = 9; x := 5 |- 9 = z
+    -/
+    rw [h]
+
+  example (h : z = 9) : let x := 5; let y := 4; x + y = z := by
+    intro x
+    simp (config := { zetaDelta := true, zeta := false })
+    /-
+    New goal:
+    h : z = 9; x := 5 |- let y := 4; 5 + y = z
+    -/
+    rw [h]
+  ```
+
+* When adding new local theorems to `simp`, the system assumes that the function application arguments
+  have been annotated with `no_index`. This modification, which addresses [issue #2670](https://github.com/leanprover/lean4/issues/2670),
+  restores the Lean 3 behavior that users expect. With this modification, the following examples are now operational:
+  ```
+  example {α β : Type} {f : α × β → β → β} (h : ∀ p : α × β, f p p.2 = p.2)
+    (a : α) (b : β) : f (a, b) b = b := by
+    simp [h]
+
+  example {α β : Type} {f : α × β → β → β}
+    (a : α) (b : β) (h : f (a,b) (a,b).2 = (a,b).2) : f (a, b) b = b := by
+    simp [h]
+  ```
+  In both cases, `h` is applicable because `simp` does not index f-arguments anymore when adding `h` to the `simp`-set.
+  It's important to note, however, that global theorems continue to be indexed in the usual manner.
+
+* Improved the error messages produced by the `decide` tactic. [#3422](https://github.com/leanprover/lean4/pull/3422)
+
+* Improved auto-completion performance. [#3460](https://github.com/leanprover/lean4/pull/3460)
+
+* Improved initial language server startup performance. [#3552](https://github.com/leanprover/lean4/pull/3552)
+
+* Changed call hierarchy to sort entries and strip private header from names displayed in the call hierarchy. [#3482](https://github.com/leanprover/lean4/pull/3482)
+
+* There is now a low-level error recovery combinator in the parsing framework, primarily intended for DSLs. [#3413](https://github.com/leanprover/lean4/pull/3413)
+
+* You can now write `termination_by?` after a declaration to see the automatically inferred
+  termination argument, and turn it into a `termination_by …` clause using the “Try this” widget or a code action. [#3514](https://github.com/leanprover/lean4/pull/3514)
+
+* A large fraction of `Std` has been moved into the Lean repository.
+  This was motivated by:
+  1. Making universally useful tactics such as `ext`, `by_cases`, `change at`,
+    `norm_cast`, `rcases`, `simpa`, `simp?`, `omega`, and `exact?`
+    available to all users of Lean, without imports.
+  2. Minimizing the syntactic changes between plain Lean and Lean with `import Std`.
+  3. Simplifying the development process for the basic data types
+     `Nat`, `Int`, `Fin` (and variants such as `UInt64`), `List`, `Array`,
+     and `BitVec` as we begin making the APIs and simp normal forms for these types
+     more complete and consistent.
+  4. Laying the groundwork for the Std roadmap, as a library focused on
+     essential datatypes not provided by the core langauge (e.g. `RBMap`)
+     and utilities such as basic IO.
+  While we have achieved most of our initial aims in `v4.7.0-rc1`,
+  some upstreaming will continue over the coming months.
+
+* The `/` and `%` notations in `Int` now use `Int.ediv` and `Int.emod`
+  (i.e. the rounding conventions have changed).
+  Previously `Std` overrode these notations, so this is no change for users of `Std`.
+  There is now kernel support for these functions.
+  [#3376](https://github.com/leanprover/lean4/pull/3376).
+
+* `omega`, our integer linear arithmetic tactic, is now availabe in the core langauge.
+  * It is supplemented by a preprocessing tactic `bv_omega` which can solve goals about `BitVec`
+    which naturally translate into linear arithmetic problems.
+    [#3435](https://github.com/leanprover/lean4/pull/3435).
+  * `omega` now has support for `Fin` [#3427](https://github.com/leanprover/lean4/pull/3427),
+    the `<<<` operator [#3433](https://github.com/leanprover/lean4/pull/3433).
+  * During the port `omega` was modified to no longer identify atoms up to definitional equality
+    (so in particular it can no longer prove `id x ≤ x`). [#3525](https://github.com/leanprover/lean4/pull/3525).
+    This may cause some regressions.
+    We plan to provide a general purpose preprocessing tactic later, or an `omega!` mode.
+  * `omega` is now invoked in Lean's automation for termination proofs
+    [#3503](https://github.com/leanprover/lean4/pull/3503) as well as in
+    array indexing proofs [#3515](https://github.com/leanprover/lean4/pull/3515).
+    This automation will be substantially revised in the medium term,
+    and while `omega` does help automate some proofs, we plan to make this much more robust.
+
+* The library search tactics `exact?` and `apply?` that were originally in
+  Mathlib are now available in Lean itself.  These use the implementation using
+  lazy discrimination trees from `Std`, and thus do not require a disk cache but
+  have a slightly longer startup time.  The order used for selection lemmas has
+  changed as well to favor goals purely based on how many terms in the head
+  pattern match the current goal.
+
+* The `solve_by_elim` tactic has been ported from `Std` to Lean so that library
+  search can use it.
+
+* New `#check_tactic` and `#check_simp` commands have been added.  These are
+  useful for checking tactics (particularly `simp`) behave as expected in test
+  suites.
+
+* Previously, app unexpanders would only be applied to entire applications. However, some notations produce
+  functions, and these functions can be given additional arguments. The solution so far has been to write app unexpanders so that they can take an arbitrary number of additional arguments. However this leads to misleading hover information in the Infoview. For example, while `HAdd.hAdd f g 1` pretty prints as `(f + g) 1`, hovering over `f + g` shows `f`. There is no way to fix the situation from within an app unexpander; the expression position for `HAdd.hAdd f g` is absent, and app unexpanders cannot register TermInfo.
+
+  This commit changes the app delaborator to try running app unexpanders on every prefix of an application, from longest to shortest prefix. For efficiency, it is careful to only try this when app delaborators do in fact exist for the head constant, and it also ensures arguments are only delaborated once. Then, in `(f + g) 1`, the `f + g` gets TermInfo registered for that subexpression, making it properly hoverable.
+
+  [#3375](https://github.com/leanprover/lean4/pull/3375)
+
+Breaking changes:
+* `Lean.withTraceNode` and variants got a stronger `MonadAlwaysExcept` assumption to
+  fix trace trees not being built on elaboration runtime exceptions. Instances for most elaboration
+  monads built on `EIO Exception` should be synthesized automatically.
+* The `match ... with.` and `fun.` notations previously in Std have been replaced by
+  `nomatch ...` and `nofun`. [#3279](https://github.com/leanprover/lean4/pull/3279) and [#3286](https://github.com/leanprover/lean4/pull/3286)
+
+
+Other improvements:
+* several bug fixes for `simp`:
+  * we should not crash when `simp` loops [#3269](https://github.com/leanprover/lean4/pull/3269)
+  * `simp` gets stuck on `autoParam` [#3315](https://github.com/leanprover/lean4/pull/3315)
+  * `simp` fails when custom discharger makes no progress [#3317](https://github.com/leanprover/lean4/pull/3317)
+  * `simp` fails to discharge `autoParam` premises even when it can reduce them to `True` [#3314](https://github.com/leanprover/lean4/pull/3314)
+  * `simp?` suggests generated equations lemma names, fixes [#3547](https://github.com/leanprover/lean4/pull/3547) [#3573](https://github.com/leanprover/lean4/pull/3573)
+* fixes for `match` expressions:
+  * fix regression with builtin literals [#3521](https://github.com/leanprover/lean4/pull/3521)
+  * accept `match` when patterns cover all cases of a `BitVec` finite type [#3538](https://github.com/leanprover/lean4/pull/3538)
+  * fix matching `Int` literals [#3504](https://github.com/leanprover/lean4/pull/3504)
+  * patterns containing int values and constructors [#3496](https://github.com/leanprover/lean4/pull/3496)
+* improve `termination_by` error messages [#3255](https://github.com/leanprover/lean4/pull/3255)
+* fix `rename_i` in macros, fixes [#3553](https://github.com/leanprover/lean4/pull/3553) [#3581](https://github.com/leanprover/lean4/pull/3581)
+* fix excessive resource usage in `generalize`, fixes [#3524](https://github.com/leanprover/lean4/pull/3524) [#3575](https://github.com/leanprover/lean4/pull/3575)
+* an equation lemma with autoParam arguments fails to rewrite, fixing [#2243](https://github.com/leanprover/lean4/pull/2243) [#3316](https://github.com/leanprover/lean4/pull/3316)
+* `add_decl_doc` should check that declarations are local [#3311](https://github.com/leanprover/lean4/pull/3311)
+* instantiate the types of inductives with the right parameters, closing [#3242](https://github.com/leanprover/lean4/pull/3242) [#3246](https://github.com/leanprover/lean4/pull/3246)
+* New simprocs for many basic types. [#3407](https://github.com/leanprover/lean4/pull/3407)
+
+Lake fixes:
+* Warn on fetch cloud release failure [#3401](https://github.com/leanprover/lean4/pull/3401)
+* Cloud release trace & `lake build :release` errors [#3248](https://github.com/leanprover/lean4/pull/3248)
+
+v4.6.1
+---------
+* Backport of [#3552](https://github.com/leanprover/lean4/pull/3552) fixing a performance regression
+  in server startup.
+
 v4.6.0
 ---------
 
 * Add custom simplification procedures (aka `simproc`s) to `simp`. Simprocs can be triggered by the simplifier on a specified term-pattern. Here is an small example:
-```lean
-import Lean.Meta.Tactic.Simp.BuiltinSimprocs.Nat
+  ```lean
+  import Lean.Meta.Tactic.Simp.BuiltinSimprocs.Nat
 
-def foo (x : Nat) : Nat :=
-  x + 10
+  def foo (x : Nat) : Nat :=
+    x + 10
 
-/--
-The `simproc` `reduceFoo` is invoked on terms that match the pattern `foo _`.
--/
-simproc reduceFoo (foo _) :=
-  /- A term of type `Expr → SimpM Step -/
-  fun e => do
+  /--
+  The `simproc` `reduceFoo` is invoked on terms that match the pattern `foo _`.
+  -/
+  simproc reduceFoo (foo _) :=
+    /- A term of type `Expr → SimpM Step -/
+    fun e => do
+      /-
+      The `Step` type has three constructors: `.done`, `.visit`, `.continue`.
+      * The constructor `.done` instructs `simp` that the result does
+        not need to be simplied further.
+      * The constructor `.visit` instructs `simp` to visit the resulting expression.
+      * The constructor `.continue` instructs `simp` to try other simplification procedures.
+
+      All three constructors take a `Result`. The `.continue` contructor may also take `none`.
+      `Result` has two fields `expr` (the new expression), and `proof?` (an optional proof).
+       If the new expression is definitionally equal to the input one, then `proof?` can be omitted or set to `none`.
+      -/
+      /- `simp` uses matching modulo reducibility. So, we ensure the term is a `foo`-application. -/
+      unless e.isAppOfArity ``foo 1 do
+        return .continue
+      /- `Nat.fromExpr?` tries to convert an expression into a `Nat` value -/
+      let some n ← Nat.fromExpr? e.appArg!
+        | return .continue
+      return .done { expr := Lean.mkNatLit (n+10) }
+  ```
+  We disable simprocs support by using the command `set_option simprocs false`. This command is particularly useful when porting files to v4.6.0.
+  Simprocs can be scoped, manually added to `simp` commands, and suppressed using `-`. They are also supported by `simp?`. `simp only` does not execute any `simproc`. Here are some examples for the `simproc` defined above.
+  ```lean
+  example : x + foo 2 = 12 + x := by
+    set_option simprocs false in
+      /- This `simp` command does not make progress since `simproc`s are disabled. -/
+      fail_if_success simp
+    simp_arith
+
+  example : x + foo 2 = 12 + x := by
+    /- `simp only` must not use the default simproc set. -/
+    fail_if_success simp only
+    simp_arith
+
+  example : x + foo 2 = 12 + x := by
     /-
-    The `Step` type has three constructors: `.done`, `.visit`, `.continue`.
-    * The constructor `.done` instructs `simp` that the result does
-      not need to be simplied further.
-    * The constructor `.visit` instructs `simp` to visit the resulting expression.
-    * The constructor `.continue` instructs `simp` to try other simplification procedures.
+    `simp only` does not use the default simproc set,
+    but we can provide simprocs as arguments. -/
+    simp only [reduceFoo]
+    simp_arith
 
-    All three constructors take a `Result`. The `.continue` contructor may also take `none`.
-    `Result` has two fields `expr` (the new expression), and `proof?` (an optional proof).
-     If the new expression is definitionally equal to the input one, then `proof?` can be omitted or set to `none`.
-    -/
-    /- `simp` uses matching modulo reducibility. So, we ensure the term is a `foo`-application. -/
-    unless e.isAppOfArity ``foo 1 do
-      return .continue
-    /- `Nat.fromExpr?` tries to convert an expression into a `Nat` value -/
-    let some n ← Nat.fromExpr? e.appArg!
-      | return .continue
-    return .done { expr := Lean.mkNatLit (n+10) }
-```
-We disable simprocs support by using the command `set_option simprocs false`. This command is particularly useful when porting files to v4.6.0.
-Simprocs can be scoped, manually added to `simp` commands, and suppressed using `-`. They are also supported by `simp?`. `simp only` does not execute any `simproc`. Here are some examples for the `simproc` defined above.
-```lean
-example : x + foo 2 = 12 + x := by
-  set_option simprocs false in
-    /- This `simp` command does not make progress since `simproc`s are disabled. -/
-    fail_if_success simp
-  simp_arith
-
-example : x + foo 2 = 12 + x := by
-  /- `simp only` must not use the default simproc set. -/
-  fail_if_success simp only
-  simp_arith
-
-example : x + foo 2 = 12 + x := by
-  /-
-  `simp only` does not use the default simproc set,
-  but we can provide simprocs as arguments. -/
-  simp only [reduceFoo]
-  simp_arith
-
-example : x + foo 2 = 12 + x := by
-  /- We can use `-` to disable `simproc`s. -/
-  fail_if_success simp [-reduceFoo]
-  simp_arith
-```
-The command `register_simp_attr <id>` now creates a `simp` **and** a `simproc` set with the name `<id>`. The following command instructs Lean to insert the `reduceFoo` simplification procedure into the set `my_simp`. If no set is specified, Lean uses the default `simp` set.
-```lean
-simproc [my_simp] reduceFoo (foo _) := ...
-```
+  example : x + foo 2 = 12 + x := by
+    /- We can use `-` to disable `simproc`s. -/
+    fail_if_success simp [-reduceFoo]
+    simp_arith
+  ```
+  The command `register_simp_attr <id>` now creates a `simp` **and** a `simproc` set with the name `<id>`. The following command instructs Lean to insert the `reduceFoo` simplification procedure into the set `my_simp`. If no set is specified, Lean uses the default `simp` set.
+  ```lean
+  simproc [my_simp] reduceFoo (foo _) := ...
+  ```
 
 * The syntax of the `termination_by` and `decreasing_by` termination hints is overhauled:
 
@@ -214,7 +533,7 @@ simproc [my_simp] reduceFoo (foo _) := ...
   and hence greatly reduces the reliance on costly structure eta reduction. This has a large impact on mathlib,
   reducing total CPU instructions by 3% and enabling impactful refactors like leanprover-community/mathlib4#8386
   which reduces the build time by almost 20%.
-  See PR [#2478](https://github.com/leanprover/lean4/pull/2478) and RFC [#2451](https://github.com/leanprover/lean4/issues/2451).
+  See [PR #2478](https://github.com/leanprover/lean4/pull/2478) and [RFC #2451](https://github.com/leanprover/lean4/issues/2451).
 
 * Add pretty printer settings to omit deeply nested terms (`pp.deepTerms false` and `pp.deepTerms.threshold`) ([PR #3201](https://github.com/leanprover/lean4/pull/3201))
 
@@ -233,7 +552,7 @@ Other improvements:
 * produce simpler proof terms in `rw` [#3121](https://github.com/leanprover/lean4/pull/3121)
 * fuse nested `mkCongrArg` calls in proofs generated by `simp` [#3203](https://github.com/leanprover/lean4/pull/3203)
 * `induction using` followed by a general term [#3188](https://github.com/leanprover/lean4/pull/3188)
-* allow generalization in `let` [#3060](https://github.com/leanprover/lean4/pull/3060, fixing [#3065](https://github.com/leanprover/lean4/issues/3065)
+* allow generalization in `let` [#3060](https://github.com/leanprover/lean4/pull/3060), fixing [#3065](https://github.com/leanprover/lean4/issues/3065)
 * reducing out-of-bounds `swap!` should return `a`, not `default`` [#3197](https://github.com/leanprover/lean4/pull/3197), fixing [#3196](https://github.com/leanprover/lean4/issues/3196)
 * derive `BEq` on structure with `Prop`-fields [#3191](https://github.com/leanprover/lean4/pull/3191), fixing [#3140](https://github.com/leanprover/lean4/issues/3140)
 * refine through more `casesOnApp`/`matcherApp` [#3176](https://github.com/leanprover/lean4/pull/3176), fixing [#3175](https://github.com/leanprover/lean4/pull/3175)

default.nix

@@ -1,9 +0,0 @@
-# used for `nix-shell https://github.com/leanprover/lean4/archive/master.tar.gz -A nix`
-{ nix = (import ./shell.nix {}).nix; } //
-(import (
-  fetchTarball {
-    url = "https://github.com/edolstra/flake-compat/archive/c75e76f80c57784a6734356315b306140646ee84.tar.gz";
-    sha256 = "071aal00zp2m9knnhddgr2wqzlx6i6qa1263lv1y7bdn2w20h10h"; }
-) {
-  src =  ./.;
-}).defaultNix

doc/SUMMARY.md

@@ -89,5 +89,6 @@
 - [Testing](./dev/testing.md)
 - [Debugging](./dev/debugging.md)
 - [Commit Convention](./dev/commit_convention.md)
+- [Release checklist](./dev/release_checklist.md)
 - [Building This Manual](./dev/mdbook.md)
 - [Foreign Function Interface](./dev/ffi.md)

doc/dev/bootstrap.md

@@ -81,20 +81,8 @@ or using Github CLI with
 gh workflow run update-stage0.yml
 ```
 
-Leaving stage0 updates to the CI automation is preferrable, but should you need
-to do it locally, you can use `make update-stage0` in `build/release`, to
-update `stage0` from `stage1`, `make -C stageN update-stage0` to update from
-another stage, or `nix run .#update-stage0-commit` to update using nix.
-
-Updates to `stage0` should be their own commits in the Git history. So should
-you have to include the stage0 update in your PR (rather than using above
-automation after merging changes), commit your work before running `make
-update-stage0`, commit the updated `stage0` compiler code with the commit
-message:
-```
-chore: update stage0
-```
-and coordinate with the admins to not squash your PR.
+Leaving stage0 updates to the CI automation is preferable, but should you need to do it locally, you can use `make update-stage0-commit` in `build/release` to update `stage0` from `stage1` or `make -C stageN update-stage0-commit` to update from another stage.
+This command will automatically stage the updated files and introduce a commit, so make sure to commit your work before that. Then coordinate with the admins to not squash your PR so that stage 0 updates are preserved as separate commits.
 
 ## Further Bootstrapping Complications
 

doc/dev/ffi.md

@@ -111,6 +111,15 @@ if (lean_io_result_is_ok(res)) {
 lean_io_mark_end_initialization();
 ```
 
+In addition, any other thread not spawned by the Lean runtime itself must be initialized for Lean use by calling
+```c
+void lean_initialize_thread();
+```
+and should be finalized in order to free all thread-local resources by calling
+```c
+void lean_finalize_thread();
+```
+
 ## `@[extern]` in the Interpreter
 
 The interpreter can run Lean declarations for which symbols are available in loaded shared libraries, which includes `@[extern]` declarations.

doc/dev/index.md

@@ -74,3 +74,9 @@ Lean's build process uses [`ccache`](https://ccache.dev/) if it is
 installed to speed up recompilation of the generated C code. Without
 `ccache`, you'll likely spend more time than necessary waiting on
 rebuilds - it's a good idea to make sure it's installed.
+
+### `prelude`
+Unlike most Lean projects, all submodules of the `Lean` module begin with the
+`prelude` keyword. This disables the automated import of `Init`, meaning that
+developers need to figure out their own subset of `Init` to import. This is done
+such that changing files in `Init` doesn't force a full rebuild of `Lean`.

doc/dev/release_checklist.md

@@ -0,0 +1,229 @@
+# Releasing a stable version
+
+This checklist walks you through releasing a stable version.
+See below for the checklist for release candidates.
+
+We'll use `v4.6.0` as the intended release version as a running example.
+
+- One week before the planned release, ensure that someone has written the first draft of the release blog post
+- `git checkout releases/v4.6.0`
+  (This branch should already exist, from the release candidates.)
+- `git pull`
+- In `src/CMakeLists.txt`, verify you see
+  - `set(LEAN_VERSION_MINOR 6)` (for whichever `6` is appropriate)
+  - `set(LEAN_VERSION_IS_RELEASE 1)`
+  - (both of these should already be in place from the release candidates)
+- It is possible that the `v4.6.0` section of `RELEASES.md` is out of sync between
+  `releases/v4.6.0` and `master`. This should be reconciled:
+  - Run `git diff master RELEASES.md`.
+  - You should expect to see additons on `master` in the `v4.7.0-rc1` section; ignore these.
+    (i.e. the new release notes for the upcoming release candidate).
+  - Reconcile discrepancies in the `v4.6.0` section,
+    usually via copy and paste and a commit to `releases/v4.6.0`.
+- `git tag v4.6.0`
+- `git push $REMOTE v4.6.0`, where `$REMOTE` is the upstream Lean repository (e.g., `origin`, `upstream`)
+- Now wait, while CI runs.
+  - You can monitor this at `https://github.com/leanprover/lean4/actions/workflows/ci.yml`,
+    looking for the `v4.6.0` tag.
+  - This step can take up to an hour.
+  - If you are intending to cut the next release candidate on the same day,
+    you may want to start on the release candidate checklist now.
+- Go to https://github.com/leanprover/lean4/releases and verify that the `v4.6.0` release appears.
+  - Edit the release notes on Github to select the "Set as the latest release".
+  - Copy and paste the Github release notes from the previous releases candidate for this version
+    (e.g. `v4.6.0-rc1`), and quickly sanity check.
+- Next, we will move a curated list of downstream repos to the latest stable release.
+  - For each of the repositories listed below:
+    - Make a PR to `master`/`main` changing the toolchain to `v4.6.0`
+      - Update the toolchain file
+      - In the Lakefile, if there are dependencies on specific version tags of dependencies that you've already pushed as part of this process, update them to the new tag.
+        If they depend on `main` or `master`, don't change this; you've just updated the dependency, so it will work and be saved in the manifest
+      - Run `lake update`
+      - The PR title should be "chore: bump toolchain to v4.6.0".
+    - Merge the PR once CI completes.
+    - Create the tag `v4.6.0` from `master`/`main` and push it.
+    - Merge the tag `v4.6.0` into the `stable` branch and push it.
+  - We do this for the repositories:
+    - [lean4checker](https://github.com/leanprover/lean4checker)
+      - No dependencies
+      - Note: `lean4checker` uses a different version tagging scheme: use `toolchain/v4.6.0` rather than `v4.6.0`.
+      - Toolchain bump PR
+      - Create and push the tag
+      - Merge the tag into `stable`
+    - [Std](https://github.com/leanprover-community/std4)
+      - No dependencies
+      - Toolchain bump PR
+      - Create and push the tag
+      - Merge the tag into `stable`
+    - [ProofWidgets4](https://github.com/leanprover-community/ProofWidgets4)
+      - Dependencies: `Std`
+      - Note on versions and branches:
+        - `ProofWidgets` uses a sequential version tagging scheme, e.g. `v0.0.29`,
+          which does not refer to the toolchain being used.
+        - Make a new release in this sequence after merging the toolchain bump PR.
+        - `ProofWidgets` does not maintain a `stable` branch.
+      - Toolchain bump PR
+      - Create and push the tag, following the version convention of the repository
+    - [Aesop](https://github.com/leanprover-community/aesop)
+      - Dependencies: `Std`
+      - Toolchain bump PR including updated Lake manifest
+      - Create and push the tag
+      - Merge the tag into `stable`
+    - [doc-gen4](https://github.com/leanprover/doc-gen4)
+      - Dependencies: exist, but they're not part of the release workflow
+      - Toolchain bump PR including updated Lake manifest
+      - Create and push the tag
+      - There is no `stable` branch; skip this step
+    - [import-graph](https://github.com/leanprover-community/import-graph)
+      - Toolchain bump PR including updated Lake manifest
+      - Create and push the tag
+      - There is no `stable` branch; skip this step
+    - [Mathlib](https://github.com/leanprover-community/mathlib4)
+      - Dependencies: `Aesop`, `ProofWidgets4`, `lean4checker`, `Std`, `doc-gen4`, `import-graph`
+      - Toolchain bump PR notes:
+        - In addition to updating the `lean-toolchain` and `lakefile.lean`,
+          in `.github/workflows/build.yml.in` in the `lean4checker` section update the line
+          `git checkout toolchain/v4.6.0` to the appropriate tag,
+          and then run `.github/workflows/mk_build_yml.sh`. Coordinate with
+          a Mathlib maintainer to get this merged.
+        - Push the PR branch to the main Mathlib repository rather than a fork, or CI may not work reliably
+        - Create and push the tag
+        - Create a new branch from the tag, push it, and open a pull request against `stable`.
+          Coordinate with a Mathlib maintainer to get this merged.
+    - [REPL](https://github.com/leanprover-community/repl)
+      - Dependencies: `Mathlib` (for test code)
+      - Note that there are two copies of `lean-toolchain`/`lakefile.lean`:
+        in the root, and in `test/Mathlib/`. Edit both, and run `lake update` in both directories.
+      - Toolchain bump PR including updated Lake manifest
+      - Create and push the tag
+      - Merge the tag into `stable`
+- Merge the release announcement PR for the Lean website - it will be deployed automatically
+- Finally, make an announcement!
+  This should go in https://leanprover.zulipchat.com/#narrow/stream/113486-announce, with topic `v4.6.0`.
+  Please see previous announcements for suggested language.
+  You will want a few bullet points for main topics from the release notes.
+  Link to the blog post from the Zulip announcement.
+- Make sure that whoever is handling social media knows the release is out.
+
+## Optimistic(?) time estimates:
+- Initial checks and push the tag: 30 minutes.
+- Note that if `RELEASES.md` has discrepancies this could take longer!
+- Waiting for the release: 60 minutes.
+- Fixing release notes: 10 minutes.
+- Bumping toolchains in downstream repositories, up to creating the Mathlib PR: 30 minutes.
+- Waiting for Mathlib CI and bors: 120 minutes.
+- Finalizing Mathlib tags and stable branch, and updating REPL: 15 minutes.
+- Posting announcement and/or blog post: 20 minutes.
+
+# Creating a release candidate.
+
+This checklist walks you through creating the first release candidate for a version of Lean.
+
+We'll use `v4.7.0-rc1` as the intended release version in this example.
+
+- Decide which nightly release you want to turn into a release candidate.
+  We will use `nightly-2024-02-29` in this example.
+- It is essential that Std and Mathlib already have reviewed branches compatible with this nightly.
+  - Check that both Std and Mathlib's `bump/v4.7.0` branch contain `nightly-2024-02-29`
+    in their `lean-toolchain`.
+  - The steps required to reach that state are beyond the scope of this checklist, but see below!
+- Create the release branch from this nightly tag:
+    ```
+    git remote add nightly https://github.com/leanprover/lean4-nightly.git
+    git fetch nightly tag nightly-2024-02-29
+    git checkout nightly-2024-02-29
+    git checkout -b releases/v4.7.0
+    ```
+- In `RELEASES.md` remove `(development in progress)` from the `v4.7.0` section header.
+- Our current goal is to have written release notes only about major language features or breaking changes,
+  and to rely on automatically generated release notes for bugfixes and minor changes.
+  - Do not wait on `RELEASES.md` being perfect before creating the `release/v4.7.0` branch. It is essential to choose the nightly which will become the release candidate as early as possible, to avoid confusion.
+  - If there are major changes not reflected in `RELEASES.md` already, you may need to solicit help from the authors.
+  - Minor changes and bug fixes do not need to be documented in `RELEASES.md`: they will be added automatically on the Github release page.
+  - Commit your changes to `RELEASES.md`, and push.
+  - Remember that changes to `RELEASES.md` after you have branched `releases/v4.7.0` should also be cherry-picked back to `master`.
+- In `src/CMakeLists.txt`,
+  - verify that you see `set(LEAN_VERSION_MINOR 7)` (for whichever `7` is appropriate); this should already have been updated when the development cycle began.
+  - `set(LEAN_VERSION_IS_RELEASE 1)` (this should be a change; on `master` and nightly releases it is always `0`).
+  - Commit your changes to `src/CMakeLists.txt`, and push.
+- `git tag v4.7.0-rc1`
+- `git push origin v4.7.0-rc1`
+- Now wait, while CI runs.
+  - You can monitor this at `https://github.com/leanprover/lean4/actions/workflows/ci.yml`, looking for the `v4.7.0-rc1` tag.
+  - This step can take up to an hour.
+- Once the release appears at https://github.com/leanprover/lean4/releases/
+  - Edit the release notes on Github to select the "Set as a pre-release box".
+  - Copy the section of `RELEASES.md` for this version into the Github release notes.
+  - Use the title "Changes since v4.6.0 (from RELEASES.md)"
+  - Then in the "previous tag" dropdown, select `v4.6.0`, and click "Generate release notes".
+  - This will add a list of all the commits since the last stable version.
+    - Delete anything already mentioned in the hand-written release notes above.
+    - Delete "update stage0" commits, and anything with a completely inscrutable commit message.
+    - Briefly rearrange the remaining items by category (e.g. `simp`, `lake`, `bug fixes`),
+      but for minor items don't put any work in expanding on commit messages.
+  - (How we want to release notes to look is evolving: please update this section if it looks wrong!)
+- Next, we will move a curated list of downstream repos to the release candidate.
+  - This assumes that there is already a *reviewed* branch `bump/v4.7.0` on each repository
+    containing the required adaptations (or no adaptations are required).
+    The preparation of this branch is beyond the scope of this document.
+  - For each of the target repositories:
+    - Checkout the `bump/v4.7.0` branch.
+    - Verify that the `lean-toolchain` is set to the nightly from which the release candidate was created.
+    - `git merge origin/master`
+    - Change the `lean-toolchain` to `leanprover/lean4:v4.7.0-rc1`
+    - In `lakefile.lean`, change any dependencies which were using `nightly-testing` or `bump/v4.7.0` branches
+      back to `master` or `main`, and run `lake update` for those dependencies.
+    - Run `lake build` to ensure that dependencies are found (but it's okay to stop it after a moment).
+    - `git commit`
+    - `git push`
+    - Open a PR from `bump/v4.7.0` to `master`, and either merge it yourself after CI, if appropriate,
+      or notify the maintainers that it is ready to go.
+    - Once this PR has been merged, tag `master` with `v4.7.0-rc1` and push this tag.
+  - We do this for the same list of repositories as for stable releases, see above.
+    As above, there are dependencies between these, and so the process above is iterative.
+    It greatly helps if you can merge the `bump/v4.7.0` PRs yourself!
+  - For Std/Aesop/Mathlib, which maintain a `nightly-testing` branch, make sure there is a tag
+    `nightly-testing-2024-02-29` with date corresponding to the nightly used for the release
+    (create it if not), and then on the `nightly-testing` branch `git reset --hard master`, and force push.
+- Make an announcement!
+  This should go in https://leanprover.zulipchat.com/#narrow/stream/113486-announce, with topic `v4.7.0-rc1`.
+  Please see previous announcements for suggested language.
+  You will want a few bullet points for main topics from the release notes.
+  Please also make sure that whoever is handling social media knows the release is out.
+- Begin the next development cycle (i.e. for `v4.8.0`) on the Lean repository, by making a PR that:
+  - Updates `src/CMakeLists.txt` to say `set(LEAN_VERSION_MINOR 8)`
+  - Removes `(in development)` from the section heading in `RELEASES.md` for `v4.7.0`,
+    and creates a new `v4.8.0 (in development)` section heading.
+
+## Time estimates:
+Slightly longer than the corresponding steps for a stable release.
+Similar process, but more things go wrong.
+In particular, updating the downstream repositories is significantly more work
+(because we need to merge existing `bump/v4.7.0` branches, not just update a toolchain).
+
+# Preparing `bump/v4.7.0` branches
+
+While not part of the release process per se,
+this is a brief summary of the work that goes into updating Std/Aesop/Mathlib to new versions.
+
+Please read https://leanprover-community.github.io/contribute/tags_and_branches.html
+
+* Each repo has an unreviewed `nightly-testing` branch that
+  receives commits automatically from `master`, and
+  has its toolchain updated automatically for every nightly.
+  (Note: the aesop branch is not automated, and is updated on an as needed basis.)
+  As a consequence this branch is often broken.
+  A bot posts in the (private!) "Mathlib reviewers" stream on Zulip about the status of these branches.
+* We fix the breakages by committing directly to `nightly-testing`: there is no PR process.
+  * This can either be done by the person managing this process directly,
+    or by soliciting assistance from authors of files, or generally helpful people on Zulip!
+* Each repo has a `bump/v4.7.0` which accumulates reviewed changes adapting to new versions.
+* Once `nightly-testing` is working on a given nightly, say `nightly-2024-02-15`, we:
+  * Make sure `bump/v4.7.0` is up to date with `master` (by merging `master`, no PR necessary)
+  * Create from `bump/v4.7.0` a `bump/nightly-2024-02-15` branch.
+  * In that branch, `git merge --squash nightly-testing` to bring across changes from `nightly-testing`.
+  * Sanity check changes, commit, and make a PR to `bump/v4.7.0` from the `bump/nightly-2024-02-15` branch.
+  * Solicit review, merge the PR into `bump/v4,7,0`.
+* It is always okay to merge in the following directions:
+  `master` -> `bump/v4.7.0` -> `bump/nightly-2024-02-15` -> `nightly-testing`.
+  Please remember to push any merges you make to intermediate steps!

doc/examples/bintree.lean

@@ -277,14 +277,13 @@ theorem BinTree.find_insert (b : BinTree β) (k : Nat) (v : β)
     . by_cases' key < k
       cases h; apply ihr; assumption
 
-theorem BinTree.find_insert_of_ne (b : BinTree β) (h : k ≠ k') (v : β)
+theorem BinTree.find_insert_of_ne (b : BinTree β) (ne : k ≠ k') (v : β)
         : (b.insert k v).find? k' = b.find? k' := by
   let ⟨t, h⟩ := b; simp
   induction t with simp
   | leaf =>
-    split <;> (try simp) <;> split <;> (try simp)
-    have_eq k k'
-    contradiction
+    intros le
+    exact Nat.lt_of_le_of_ne le ne
   | node left key value right ihl ihr =>
     let .node hl hr bl br := h
     specialize ihl bl

doc/flake.nix

@@ -27,7 +27,7 @@
         src = inputs.mdBook;
         cargoDeps = drv.cargoDeps.overrideAttrs (_: {
           inherit src;
-          outputHash = "sha256-1YlPS6cqgxE4fjy9G8pWrpP27YrrbCDnfeyIsX81ZNw=";
+          outputHash = "sha256-CO3A9Kpp4sIvkT9X3p+GTidazk7Fn4jf0AP2PINN44A=";
         });
         doCheck = false;
       });

doc/make/index.md

@@ -12,7 +12,7 @@ Platform-Specific Setup
 - [Windows (msys2)](msys2.md)
 - [Windows (WSL)](wsl.md)
 - [macOS (homebrew)](osx-10.9.md)
-- Linux/macOS/WSL via [Nix](https://nixos.org/nix/): Call `nix-shell` in the project root. That's it.
+- Linux/macOS/WSL via [Nix](https://nixos.org/nix/): Call `nix develop` in the project root. That's it.
 
 Generic Build Instructions
 --------------------------

doc/monads/except.lean

@@ -33,7 +33,7 @@ convert the pure non-monadic value `x / y` into the required `Except` object.  S
 
 Now this return typing would get tedious if you had to include it everywhere that you call this
 function, however, Lean type inference can clean this up. For example, you can define a test
-function can calls the `divide` function and you don't need to say anything here about the fact that
+function that calls the `divide` function and you don't need to say anything here about the fact that
 it might throw an error, because that is inferred:
 -/
 def test := divide 5 0

flake.lock

@@ -1,12 +1,31 @@
 {
   "nodes": {
-    "flake-utils": {
+    "flake-compat": {
+      "flake": false,
       "locked": {
-        "lastModified": 1656928814,
-        "narHash": "sha256-RIFfgBuKz6Hp89yRr7+NR5tzIAbn52h8vT6vXkYjZoM=",
+        "lastModified": 1673956053,
+        "narHash": "sha256-4gtG9iQuiKITOjNQQeQIpoIB6b16fm+504Ch3sNKLd8=",
+        "owner": "edolstra",
+        "repo": "flake-compat",
+        "rev": "35bb57c0c8d8b62bbfd284272c928ceb64ddbde9",
+        "type": "github"
+      },
+      "original": {
+        "owner": "edolstra",
+        "repo": "flake-compat",
+        "type": "github"
+      }
+    },
+    "flake-utils": {
+      "inputs": {
+        "systems": "systems"
+      },
+      "locked": {
+        "lastModified": 1710146030,
+        "narHash": "sha256-SZ5L6eA7HJ/nmkzGG7/ISclqe6oZdOZTNoesiInkXPQ=",
         "owner": "numtide",
         "repo": "flake-utils",
-        "rev": "7e2a3b3dfd9af950a856d66b0a7d01e3c18aa249",
+        "rev": "b1d9ab70662946ef0850d488da1c9019f3a9752a",
         "type": "github"
       },
       "original": {
@@ -18,11 +37,11 @@
     "lean4-mode": {
       "flake": false,
       "locked": {
-        "lastModified": 1676498134,
-        "narHash": "sha256-u3WvyKxOViZG53hkb8wd2/Og6muTecbh+NdflIgVeyk=",
+        "lastModified": 1709737301,
+        "narHash": "sha256-uT9JN2kLNKJK9c/S/WxLjiHmwijq49EgLb+gJUSDpz0=",
         "owner": "leanprover",
         "repo": "lean4-mode",
-        "rev": "2c6ef33f476fdf5eb5e4fa4fa023ba8b11372440",
+        "rev": "f1f24c15134dee3754b82c9d9924866fe6bc6b9f",
         "type": "github"
       },
       "original": {
@@ -31,34 +50,35 @@
         "type": "github"
       }
     },
-    "lowdown-src": {
+    "libgit2": {
       "flake": false,
       "locked": {
-        "lastModified": 1633514407,
-        "narHash": "sha256-Dw32tiMjdK9t3ETl5fzGrutQTzh2rufgZV4A/BbxuD4=",
-        "owner": "kristapsdz",
-        "repo": "lowdown",
-        "rev": "d2c2b44ff6c27b936ec27358a2653caaef8f73b8",
+        "lastModified": 1697646580,
+        "narHash": "sha256-oX4Z3S9WtJlwvj0uH9HlYcWv+x1hqp8mhXl7HsLu2f0=",
+        "owner": "libgit2",
+        "repo": "libgit2",
+        "rev": "45fd9ed7ae1a9b74b957ef4f337bc3c8b3df01b5",
         "type": "github"
       },
       "original": {
-        "owner": "kristapsdz",
-        "repo": "lowdown",
+        "owner": "libgit2",
+        "repo": "libgit2",
         "type": "github"
       }
     },
     "nix": {
       "inputs": {
-        "lowdown-src": "lowdown-src",
+        "flake-compat": "flake-compat",
+        "libgit2": "libgit2",
         "nixpkgs": "nixpkgs",
         "nixpkgs-regression": "nixpkgs-regression"
       },
       "locked": {
-        "lastModified": 1657097207,
-        "narHash": "sha256-SmeGmjWM3fEed3kQjqIAO8VpGmkC2sL1aPE7kKpK650=",
+        "lastModified": 1711102798,
+        "narHash": "sha256-CXOIJr8byjolqG7eqCLa+Wfi7rah62VmLoqSXENaZnw=",
         "owner": "NixOS",
         "repo": "nix",
-        "rev": "f6316b49a0c37172bca87ede6ea8144d7d89832f",
+        "rev": "a22328066416650471c3545b0b138669ea212ab4",
         "type": "github"
       },
       "original": {
@@ -69,16 +89,33 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1653988320,
-        "narHash": "sha256-ZaqFFsSDipZ6KVqriwM34T739+KLYJvNmCWzErjAg7c=",
+        "lastModified": 1709083642,
+        "narHash": "sha256-7kkJQd4rZ+vFrzWu8sTRtta5D1kBG0LSRYAfhtmMlSo=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "2fa57ed190fd6c7c746319444f34b5917666e5c1",
+        "rev": "b550fe4b4776908ac2a861124307045f8e717c8e",
         "type": "github"
       },
       "original": {
         "owner": "NixOS",
-        "ref": "nixos-22.05-small",
+        "ref": "release-23.11",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs-old": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1581379743,
+        "narHash": "sha256-i1XCn9rKuLjvCdu2UeXKzGLF6IuQePQKFt4hEKRU5oc=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "34c7eb7545d155cc5b6f499b23a7cb1c96ab4d59",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-19.03",
         "repo": "nixpkgs",
         "type": "github"
       }
@@ -101,11 +138,11 @@
     },
     "nixpkgs_2": {
       "locked": {
-        "lastModified": 1686089707,
-        "narHash": "sha256-LTNlJcru2qJ0XhlhG9Acp5KyjB774Pza3tRH0pKIb3o=",
+        "lastModified": 1710889954,
+        "narHash": "sha256-Pr6F5Pmd7JnNEMHHmspZ0qVqIBVxyZ13ik1pJtm2QXk=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "af21c31b2a1ec5d361ed8050edd0303c31306397",
+        "rev": "7872526e9c5332274ea5932a0c3270d6e4724f3b",
         "type": "github"
       },
       "original": {
@@ -120,7 +157,23 @@
         "flake-utils": "flake-utils",
         "lean4-mode": "lean4-mode",
         "nix": "nix",
-        "nixpkgs": "nixpkgs_2"
+        "nixpkgs": "nixpkgs_2",
+        "nixpkgs-old": "nixpkgs-old"
+      }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
       }
     }
   },

flake.nix

@@ -2,6 +2,9 @@
   description = "Lean interactive theorem prover";
 
   inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+  # old nixpkgs used for portable release with older glibc (2.27)
+  inputs.nixpkgs-old.url = "github:NixOS/nixpkgs/nixos-19.03";
+  inputs.nixpkgs-old.flake = false;
   inputs.flake-utils.url = "github:numtide/flake-utils";
   inputs.nix.url = "github:NixOS/nix";
   inputs.lean4-mode = {
@@ -17,14 +20,41 @@
   #  inputs.lean4-mode.follows = "lean4-mode";
   #};
 
-  outputs = { self, nixpkgs, flake-utils, nix, lean4-mode, ... }@inputs: flake-utils.lib.eachDefaultSystem (system:
+  outputs = { self, nixpkgs, nixpkgs-old, flake-utils, nix, lean4-mode, ... }@inputs: flake-utils.lib.eachDefaultSystem (system:
     let
       pkgs = import nixpkgs {
         inherit system;
         # for `vscode-with-extensions`
         config.allowUnfree = true;
       };
+      # An old nixpkgs for creating releases with an old glibc
+      pkgsDist-old = import nixpkgs-old { inherit system; };
+      # An old nixpkgs for creating releases with an old glibc
+      pkgsDist-old-aarch = import nixpkgs-old { localSystem.config = "aarch64-unknown-linux-gnu"; };
+
       lean-packages = pkgs.callPackage (./nix/packages.nix) { src = ./.; inherit nix lean4-mode; };
+
+      devShellWithDist = pkgsDist: pkgs.mkShell.override {
+	  stdenv = pkgs.overrideCC pkgs.stdenv lean-packages.llvmPackages.clang;
+	} ({
+	  buildInputs = with pkgs; [
+	    cmake gmp ccache
+	    lean-packages.llvmPackages.llvm  # llvm-symbolizer for asan/lsan
+	    # TODO: only add when proven to not affect the flakification
+	    #pkgs.python3
+	  ];
+	  # https://github.com/NixOS/nixpkgs/issues/60919
+	  hardeningDisable = [ "all" ];
+	  # more convenient `ctest` output
+	  CTEST_OUTPUT_ON_FAILURE = 1;
+	} // pkgs.lib.optionalAttrs pkgs.stdenv.isLinux {
+	  GMP = pkgsDist.gmp.override { withStatic = true; };
+	  GLIBC = pkgsDist.glibc;
+	  GLIBC_DEV = pkgsDist.glibc.dev;
+	  GCC_LIB = pkgsDist.gcc.cc.lib;
+	  ZLIB = pkgsDist.zlib;
+	  GDB = pkgsDist.gdb;
+	});
     in {
       packages = lean-packages // rec {
         debug = lean-packages.override { debug = true; };
@@ -49,7 +79,10 @@
       };
       defaultPackage = lean-packages.lean-all;
 
-      inherit (lean-packages) devShell;
+      # The default development shell for working on lean itself
+      devShells.default = devShellWithDist pkgs;
+      devShells.oldGlibc = devShellWithDist pkgsDist-old;
+      devShells.oldGlibcAArch = devShellWithDist pkgsDist-old-aarch;
 
       checks.lean = lean-packages.test;
     }) // rec {

nix/bootstrap.nix

@@ -65,12 +65,7 @@ rec {
     installPhase = ''
       mkdir -p $out/bin $out/lib/lean
       mv bin/lean $out/bin/
-      mv lib/lean/libleanshared.* $out/lib/lean
-   '' + lib.optionalString stdenv.isDarwin ''
-      for lib in $(otool -L $out/bin/lean | tail -n +2 | cut -d' ' -f1); do
-        if [[ "$lib" == *lean* ]]; then install_name_tool -change "$lib" "$out/lib/lean/$(basename $lib)" $out/bin/lean; fi
-      done
-      otool -L $out/bin/lean
+      mv lib/lean/*.{so,dylib} $out/lib/lean
     '';
     meta.mainProgram = "lean";
   });
@@ -120,29 +115,35 @@ rec {
       iTree = symlinkJoin { name = "ileans"; paths = map (l: l.iTree) stdlib; };
       Leanc = build { name = "Leanc"; src = lean-bin-tools-unwrapped.leanc_src; deps = stdlib; roots = [ "Leanc" ]; };
       stdlibLinkFlags = "-L${Init.staticLib} -L${Lean.staticLib} -L${Lake.staticLib} -L${leancpp}/lib/lean";
+      libInit_shared = runCommand "libInit_shared" { buildInputs = [ stdenv.cc ]; libName = "libInit_shared${stdenv.hostPlatform.extensions.sharedLibrary}"; } ''
+        mkdir $out
+        LEAN_CC=${stdenv.cc}/bin/cc ${lean-bin-tools-unwrapped}/bin/leanc -shared -Wl,-Bsymbolic \
+          -Wl,--whole-archive -lInit ${leancpp}/lib/libleanrt_initial-exec.a -Wl,--no-whole-archive -lstdc++ -lm ${stdlibLinkFlags} \
+          $(${llvmPackages.libllvm.dev}/bin/llvm-config --ldflags --libs) \
+          -o $out/$libName
+      '';
       leanshared = runCommand "leanshared" { buildInputs = [ stdenv.cc ]; libName = "libleanshared${stdenv.hostPlatform.extensions.sharedLibrary}"; } ''
         mkdir $out
-        LEAN_CC=${stdenv.cc}/bin/cc ${lean-bin-tools-unwrapped}/bin/leanc -shared ${lib.optionalString stdenv.isLinux "-Wl,-Bsymbolic"} \
-          ${if stdenv.isDarwin then "-Wl,-force_load,${Init.staticLib}/libInit.a -Wl,-force_load,${Lean.staticLib}/libLean.a -Wl,-force_load,${leancpp}/lib/lean/libleancpp.a ${leancpp}/lib/libleanrt_initial-exec.a -lc++"
-            else "-Wl,--whole-archive -lInit -lLean -lleancpp ${leancpp}/lib/libleanrt_initial-exec.a -Wl,--no-whole-archive -lstdc++"} -lm ${stdlibLinkFlags} \
+        LEAN_CC=${stdenv.cc}/bin/cc ${lean-bin-tools-unwrapped}/bin/leanc -shared -Wl,-Bsymbolic \
+          ${libInit_shared}/* -Wl,--whole-archive -lLean -lleancpp -Wl,--no-whole-archive -lstdc++ -lm ${stdlibLinkFlags} \
           $(${llvmPackages.libllvm.dev}/bin/llvm-config --ldflags --libs) \
           -o $out/$libName
       '';
       mods = foldl' (mods: pkg: mods // pkg.mods) {} stdlib;
       print-paths = Lean.makePrintPathsFor [] mods;
       leanc = writeShellScriptBin "leanc" ''
-        LEAN_CC=${stdenv.cc}/bin/cc ${Leanc.executable}/bin/leanc -I${lean-bin-tools-unwrapped}/include ${stdlibLinkFlags} -L${leanshared} "$@"
+        LEAN_CC=${stdenv.cc}/bin/cc ${Leanc.executable}/bin/leanc -I${lean-bin-tools-unwrapped}/include ${stdlibLinkFlags} -L${libInit_shared} -L${leanshared} "$@"
       '';
       lean = runCommand "lean" { buildInputs = lib.optional stdenv.isDarwin darwin.cctools; } ''
         mkdir -p $out/bin
-        ${leanc}/bin/leanc ${leancpp}/lib/lean.cpp.o ${leanshared}/* -o $out/bin/lean
+        ${leanc}/bin/leanc ${leancpp}/lib/lean.cpp.o ${libInit_shared}/* ${leanshared}/* -o $out/bin/lean
       '';
       # derivation following the directory layout of the "basic" setup, mostly useful for running tests
       lean-all = stdenv.mkDerivation {
         name = "lean-${desc}";
         buildCommand = ''
           mkdir -p $out/bin $out/lib/lean
-          ln -sf ${leancpp}/lib/lean/* ${lib.concatMapStringsSep " " (l: "${l.modRoot}/* ${l.staticLib}/*") (lib.reverseList stdlib)} ${leanshared}/* $out/lib/lean/
+          ln -sf ${leancpp}/lib/lean/* ${lib.concatMapStringsSep " " (l: "${l.modRoot}/* ${l.staticLib}/*") (lib.reverseList stdlib)} ${libInit_shared}/* ${leanshared}/* $out/lib/lean/
           # put everything in a single final derivation so `IO.appDir` references work
           cp ${lean}/bin/lean ${leanc}/bin/leanc ${Lake-Main.executable}/bin/lake $out/bin
           # NOTE: `lndir` will not override existing `bin/leanc`
@@ -169,10 +170,11 @@ rec {
           ln -sf ${lean-all}/* .
         '';
         buildPhase = ''
-          ctest --output-on-failure -E 'leancomptest_(doc_example|foreign)' -j$NIX_BUILD_CORES
+          ctest --output-junit test-results.xml --output-on-failure -E 'leancomptest_(doc_example|foreign)' -j$NIX_BUILD_CORES
         '';
         installPhase = ''
-          touch $out
+          mkdir $out
+          mv test-results.xml $out
         '';
       };
       update-stage0 =

nix/buildLeanPackage.nix

@@ -10,7 +10,7 @@ lib.makeOverridable (
   staticLibDeps ? [],
   # Whether to wrap static library inputs in a -Wl,--start-group [...] -Wl,--end-group to ensure dependencies are resolved.
   groupStaticLibs ? false,
-  # Shared library dependencies included at interpretation with --load-dynlib and linked to. Each derivation `shared` should contain a 
+  # Shared library dependencies included at interpretation with --load-dynlib and linked to. Each derivation `shared` should contain a
   # shared library at the path `${shared}/${shared.libName or shared.name}` and a name to link to like `-l${shared.linkName or shared.name}`.
   # These libs are also linked to in packages that depend on this one.
   nativeSharedLibs ? [],
@@ -88,9 +88,9 @@ with builtins; let
   allNativeSharedLibs =
     lib.unique (lib.flatten (nativeSharedLibs ++ (map (dep: dep.allNativeSharedLibs or []) allExternalDeps)));
 
-  # A flattened list of all static library dependencies: this and every dep module's explicitly provided `staticLibDeps`, 
+  # A flattened list of all static library dependencies: this and every dep module's explicitly provided `staticLibDeps`,
   # plus every dep module itself: `dep.staticLib`
-  allStaticLibDeps = 
+  allStaticLibDeps =
     lib.unique (lib.flatten (staticLibDeps ++ (map (dep: [dep.staticLib] ++ dep.staticLibDeps or []) allExternalDeps)));
 
   pathOfSharedLib = dep: dep.libPath or "${dep}/${dep.libName or dep.name}";
@@ -176,7 +176,7 @@ with builtins; let
       # make local "copy" so `drv`'s Nix store path doesn't end up in ccache's hash
       ln -s ${drv.c}/${drv.cPath} src.c
       # on the other hand, a debug build is pretty fast anyway, so preserve the path for gdb
-      leanc -c -o $out/$oPath $leancFlags -fPIC ${if debug then "${drv.c}/${drv.cPath} -g" else "src.c -O3 -DNDEBUG"}
+      leanc -c -o $out/$oPath $leancFlags -fPIC ${if debug then "${drv.c}/${drv.cPath} -g" else "src.c -O3 -DNDEBUG -DLEAN_EXPORTING"}
     '';
   };
   mkMod = mod: deps:
@@ -249,7 +249,7 @@ in rec {
     ${if stdenv.isDarwin then "-Wl,-force_load,${staticLib}/lib${libName}.a" else "-Wl,--whole-archive ${staticLib}/lib${libName}.a -Wl,--no-whole-archive"} \
     ${lib.concatStringsSep " " (map (d: "${d.sharedLib}/*") deps)}'';
   executable = lib.makeOverridable ({ withSharedStdlib ? true }: let
-      objPaths = map (drv: "${drv}/${drv.oPath}") (attrValues objects) ++ lib.optional withSharedStdlib "${lean-final.leanshared}/*";
+      objPaths = map (drv: "${drv}/${drv.oPath}") (attrValues objects) ++ lib.optional withSharedStdlib "${lean-final.libInit_shared}/* ${lean-final.leanshared}/*";
     in runCommand executableName { buildInputs = [ stdenv.cc leanc ]; } ''
       mkdir -p $out/bin
       leanc ${staticLibLinkWrapper (lib.concatStringsSep " " (objPaths ++ map (d: "${d}/*.a") allStaticLibDeps))} \

script/apply.lean

@@ -1,3 +1,8 @@
+/-
+Copyright (c) 2022 Sebastian Ullrich. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Sebastian Ullrich
+-/
 import Lean.Runtime
 
 abbrev M := ReaderT IO.FS.Stream IO
@@ -16,7 +21,7 @@ def mkTypedefFn (i : Nat) : M Unit := do
   emit s!"typedef obj* (*fn{i})({args}); // NOLINT\n"
   emit s!"#define FN{i}(f) reinterpret_cast<fn{i}>(lean_closure_fun(f))\n"
 
-def genSeq (n : Nat) (f : Nat → String) (sep := ", ") : String := 
+def genSeq (n : Nat) (f : Nat → String) (sep := ", ") : String :=
   List.range n |>.map f |>.intersperse sep |> .join
 
 -- make string: "obj* a1, obj* a2, ..., obj* an"

script/collideProfiles.lean

@@ -0,0 +1,28 @@
+import Lean.Util.Profiler
+
+/-!
+
+Usage:
+```sh
+lean --run ./script/collideProfiles.lean **/*.lean.json ... > merged.json
+```
+
+Merges multiple `trace.profiler.output` profiles into a single one while deduplicating samples with
+the same stack. This is useful for building cumulative profiles of medium-to-large projects because
+Firefox Profiler cannot handle hundreds of tracks and the deduplication will also ensure that the
+profile is small enough for uploading.
+
+As ordering of samples is not meaningful after this transformation, only "Call Tree" and "Flame
+Graph" are useful for such profiles.
+-/
+
+open Lean
+
+def main (args : List String) : IO Unit := do
+  let profiles ← args.toArray.mapM fun path => do
+    let json ← IO.FS.readFile ⟨path⟩
+    let profile ← IO.ofExcept $ Json.parse json
+    IO.ofExcept <| fromJson? profile
+  -- NOTE: `collide` should not be interpreted
+  let profile := Firefox.Profile.collide profiles
+  IO.println <| Json.compress <| toJson profile

script/prepare-llvm-linux.sh

@@ -25,6 +25,8 @@ cp -L llvm/bin/llvm-ar stage1/bin/
 # dependencies of the above
 $CP llvm/lib/lib{clang-cpp,LLVM}*.so* stage1/lib/
 $CP $ZLIB/lib/libz.so* stage1/lib/
+# general clang++ dependency, breaks cross-library C++ exceptions if linked statically
+$CP $GCC_LIB/lib/libgcc_s.so* stage1/lib/
 # bundle libatomic (referenced by LLVM >= 15, and required by the lean executable to run)
 $CP $GCC_LIB/lib/libatomic.so* stage1/lib/
 
@@ -60,7 +62,7 @@ fi
 # use `-nostdinc` to make sure headers are not visible by default (in particular, not to `#include_next` in the clang headers),
 # but do not change sysroot so users can still link against system libs
 echo -n " -DLEANC_INTERNAL_FLAGS='-nostdinc -isystem ROOT/include/clang' -DLEANC_CC=ROOT/bin/clang"
-echo -n " -DLEANC_INTERNAL_LINKER_FLAGS='-L ROOT/lib -L ROOT/lib/glibc ROOT/lib/glibc/libc_nonshared.a -Wl,--as-needed -static-libgcc -Wl,-Bstatic -lgmp -lunwind -Wl,-Bdynamic -Wl,--no-as-needed -fuse-ld=lld'"
+echo -n " -DLEANC_INTERNAL_LINKER_FLAGS='-L ROOT/lib -L ROOT/lib/glibc ROOT/lib/glibc/libc_nonshared.a -Wl,--as-needed -Wl,-Bstatic -lgmp -lunwind -Wl,-Bdynamic -Wl,--no-as-needed -fuse-ld=lld'"
 # when not using the above flags, link GMP dynamically/as usual
 echo -n " -DLEAN_EXTRA_LINKER_FLAGS='-Wl,--as-needed -lgmp -Wl,--no-as-needed'"
 # do not set `LEAN_CC` for tests

shell.nix

@@ -1,27 +0,0 @@
-let
-  flake = (import ./default.nix);
-  flakePkgs = flake.packages.${builtins.currentSystem};
-in { pkgs ? flakePkgs.nixpkgs, pkgsDist ? pkgs }:
-# use `shell` as default
-(attribs: attribs.shell // attribs) rec {
-  shell = pkgs.mkShell.override {
-    stdenv = pkgs.overrideCC pkgs.stdenv flakePkgs.llvmPackages.clang;
-  } (rec {
-    buildInputs = with pkgs; [
-      cmake gmp ccache
-      flakePkgs.llvmPackages.llvm  # llvm-symbolizer for asan/lsan
-    ];
-    # https://github.com/NixOS/nixpkgs/issues/60919
-    hardeningDisable = [ "all" ];
-    # more convenient `ctest` output
-    CTEST_OUTPUT_ON_FAILURE = 1;
-  } // pkgs.lib.optionalAttrs pkgs.stdenv.isLinux {
-    GMP = pkgsDist.gmp.override { withStatic = true; };
-    GLIBC = pkgsDist.glibc;
-    GLIBC_DEV = pkgsDist.glibc.dev;
-    GCC_LIB = pkgsDist.gcc.cc.lib;
-    ZLIB = pkgsDist.zlib;
-    GDB = pkgsDist.gdb;
-  });
-  nix = flake.devShell.${builtins.currentSystem};
-}

src/CMakeLists.txt

@@ -9,7 +9,7 @@ endif()
 include(ExternalProject)
 project(LEAN CXX C)
 set(LEAN_VERSION_MAJOR 4)
-set(LEAN_VERSION_MINOR 7)
+set(LEAN_VERSION_MINOR 8)
 set(LEAN_VERSION_PATCH 0)
 set(LEAN_VERSION_IS_RELEASE 0)  # This number is 1 in the release revision, and 0 otherwise.
 set(LEAN_SPECIAL_VERSION_DESC "" CACHE STRING "Additional version description like 'nightly-2018-03-11'")
@@ -299,13 +299,12 @@ if(${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
     cmake_path(GET ZLIB_LIBRARY PARENT_PATH ZLIB_LIBRARY_PARENT_PATH)
     string(APPEND LEANSHARED_LINKER_FLAGS " -L ${ZLIB_LIBRARY_PARENT_PATH}")
   endif()
-  string(APPEND LEANC_STATIC_LINKER_FLAGS " -lleancpp -lInit -lLean -lleanrt")
+  string(APPEND TOOLCHAIN_STATIC_LINKER_FLAGS " -lleancpp -lInit -lLean -lleanrt")
 elseif(${CMAKE_SYSTEM_NAME} MATCHES "Emscripten")
-  string(APPEND LEANC_STATIC_LINKER_FLAGS " -lleancpp -lInit -lLean -lnodefs.js -lleanrt")
+  string(APPEND TOOLCHAIN_STATIC_LINKER_FLAGS " -lleancpp -lInit -lLean -lnodefs.js -lleanrt")
 else()
-  string(APPEND LEANC_STATIC_LINKER_FLAGS " -Wl,--start-group -lleancpp -lLean -Wl,--end-group -Wl,--start-group -lInit -lleanrt -Wl,--end-group")
+  string(APPEND TOOLCHAIN_STATIC_LINKER_FLAGS " -Wl,--start-group -lleancpp -lLean -Wl,--end-group -Wl,--start-group -lInit -lleanrt -Wl,--end-group")
 endif()
-string(APPEND LEANC_STATIC_LINKER_FLAGS " -lLake")
 
 set(LEAN_CXX_STDLIB "-lstdc++" CACHE STRING "C++ stdlib linker flags")
 
@@ -313,8 +312,11 @@ if(${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
   set(LEAN_CXX_STDLIB "-lc++")
 endif()
 
-string(APPEND LEANC_STATIC_LINKER_FLAGS " ${LEAN_CXX_STDLIB}")
-string(APPEND LEANSHARED_LINKER_FLAGS " ${LEAN_CXX_STDLIB}")
+string(APPEND TOOLCHAIN_STATIC_LINKER_FLAGS " ${LEAN_CXX_STDLIB}")
+string(APPEND TOOLCHAIN_SHARED_LINKER_FLAGS " ${LEAN_CXX_STDLIB}")
+
+# flags for user binaries = flags for toolchain binaries + Lake
+string(APPEND LEANC_STATIC_LINKER_FLAGS " ${TOOLCHAIN_STATIC_LINKER_FLAGS} -lLake")
 
 if (LLVM)
   string(APPEND LEANSHARED_LINKER_FLAGS " -L${LLVM_CONFIG_LIBDIR} ${LLVM_CONFIG_LDFLAGS} ${LLVM_CONFIG_LIBS} ${LLVM_CONFIG_SYSTEM_LIBS}")
@@ -342,9 +344,9 @@ endif()
 
 # get rid of unused parts of C++ stdlib
 if(${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
-  string(APPEND LEANSHARED_LINKER_FLAGS " -Wl,-dead_strip")
+  string(APPEND TOOLCHAIN_SHARED_LINKER_FLAGS " -Wl,-dead_strip")
 elseif(NOT ${CMAKE_SYSTEM_NAME} MATCHES "Emscripten")
-  string(APPEND LEANSHARED_LINKER_FLAGS " -Wl,--gc-sections")
+  string(APPEND TOOLCHAIN_SHARED_LINKER_FLAGS " -Wl,--gc-sections")
 endif()
 
 if(NOT ${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
@@ -354,26 +356,20 @@ endif()
 if(${CMAKE_SYSTEM_NAME} MATCHES "Linux")
   if(BSYMBOLIC)
     string(APPEND LEANC_SHARED_LINKER_FLAGS " -Wl,-Bsymbolic")
-    string(APPEND LEANSHARED_LINKER_FLAGS " -Wl,-Bsymbolic")
+    string(APPEND TOOLCHAIN_SHARED_LINKER_FLAGS " -Wl,-Bsymbolic")
   endif()
   string(APPEND CMAKE_CXX_FLAGS " -fPIC -ftls-model=initial-exec")
   string(APPEND LEANC_EXTRA_FLAGS " -fPIC")
-  string(APPEND LEANSHARED_LINKER_FLAGS " -Wl,-rpath=\\$$ORIGIN/..:\\$$ORIGIN")
-  string(APPEND CMAKE_EXE_LINKER_FLAGS " -lleanshared -Wl,-rpath=\\\$ORIGIN/../lib:\\\$ORIGIN/../lib/lean")
+  string(APPEND TOOLCHAIN_SHARED_LINKER_FLAGS " -Wl,-rpath=\\$$ORIGIN/..:\\$$ORIGIN")
+  string(APPEND CMAKE_EXE_LINKER_FLAGS " -Wl,-rpath=\\\$ORIGIN/../lib:\\\$ORIGIN/../lib/lean")
 elseif(${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
   string(APPEND CMAKE_CXX_FLAGS " -ftls-model=initial-exec")
+  string(APPEND INIT_SHARED_LINKER_FLAGS " -install_name @rpath/libInit_shared.dylib")
   string(APPEND LEANSHARED_LINKER_FLAGS " -install_name @rpath/libleanshared.dylib")
-  string(APPEND CMAKE_EXE_LINKER_FLAGS " -lleanshared -Wl,-rpath,@executable_path/../lib -Wl,-rpath,@executable_path/../lib/lean")
+  string(APPEND CMAKE_EXE_LINKER_FLAGS " -Wl,-rpath,@executable_path/../lib -Wl,-rpath,@executable_path/../lib/lean")
 elseif(${CMAKE_SYSTEM_NAME} MATCHES "Emscripten")
   string(APPEND CMAKE_CXX_FLAGS " -fPIC")
   string(APPEND LEANC_EXTRA_FLAGS " -fPIC")
-  # We do not use dynamic linking via leanshared for Emscripten to keep things
-  # simple. (And we are not interested in `Lake` anyway.) To use dynamic
-  # linking, we would probably have to set MAIN_MODULE=2 on `leanshared`,
-  # SIDE_MODULE=2 on `lean`, and set CMAKE_SHARED_LIBRARY_SUFFIX to ".js".
-  string(APPEND CMAKE_EXE_LINKER_FLAGS " -Wl,--whole-archive -lInit -lLean -lleancpp -lleanrt ${EMSCRIPTEN_SETTINGS} -lnodefs.js -s EXIT_RUNTIME=1 -s MAIN_MODULE=1 -s LINKABLE=1 -s EXPORT_ALL=1")
-elseif(${CMAKE_SYSTEM_NAME} MATCHES "Windows")
-  string(APPEND CMAKE_EXE_LINKER_FLAGS " -lleanshared")
 endif()
 
 if(${CMAKE_SYSTEM_NAME} MATCHES "Linux")
@@ -399,7 +395,7 @@ endif()
 # are already loaded) and probably fail unless we set up LD_LIBRARY_PATH.
 if(${CMAKE_SYSTEM_NAME} MATCHES "Windows")
   # import library created by the `leanshared` target
-  string(APPEND LEANC_SHARED_LINKER_FLAGS " -lleanshared")
+  string(APPEND LEANC_SHARED_LINKER_FLAGS " -lInit_shared -lleanshared")
 elseif("${CMAKE_SYSTEM_NAME}" MATCHES "Darwin")
   string(APPEND LEANC_SHARED_LINKER_FLAGS " -Wl,-undefined,dynamic_lookup")
 endif()
@@ -505,13 +501,25 @@ string(REGEX REPLACE "^([a-zA-Z]):" "/\\1" LEAN_BIN "${CMAKE_BINARY_DIR}/bin")
 # (also looks nicer in the build log)
 file(RELATIVE_PATH LIB ${LEAN_SOURCE_DIR} ${CMAKE_BINARY_DIR}/lib)
 
+# set up libInit_shared only on Windows; see also stdlib.make.in
+if(${CMAKE_SYSTEM_NAME} MATCHES "Windows")
+  set(INIT_SHARED_LINKER_FLAGS "-Wl,--whole-archive ${CMAKE_BINARY_DIR}/lib/temp/libInit.a.export ${CMAKE_BINARY_DIR}/runtime/libleanrt_initial-exec.a -Wl,--no-whole-archive -Wl,--out-implib,${CMAKE_BINARY_DIR}/lib/lean/libInit_shared.dll.a")
+endif()
+
 if(${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
   set(LEANSHARED_LINKER_FLAGS "-Wl,-force_load,${CMAKE_BINARY_DIR}/lib/lean/libInit.a -Wl,-force_load,${CMAKE_BINARY_DIR}/lib/lean/libLean.a -Wl,-force_load,${CMAKE_BINARY_DIR}/lib/lean/libleancpp.a ${CMAKE_BINARY_DIR}/runtime/libleanrt_initial-exec.a ${LEANSHARED_LINKER_FLAGS}")
+elseif(${CMAKE_SYSTEM_NAME} MATCHES "Windows")
+  set(LEANSHARED_LINKER_FLAGS "-Wl,--whole-archive ${CMAKE_BINARY_DIR}/lib/temp/libLean.a.export -lleancpp -Wl,--no-whole-archive -lInit_shared -Wl,--out-implib,${CMAKE_BINARY_DIR}/lib/lean/libleanshared.dll.a")
 else()
   set(LEANSHARED_LINKER_FLAGS "-Wl,--whole-archive -lInit -lLean -lleancpp -Wl,--no-whole-archive ${CMAKE_BINARY_DIR}/runtime/libleanrt_initial-exec.a ${LEANSHARED_LINKER_FLAGS}")
-  if(${CMAKE_SYSTEM_NAME} MATCHES "Windows")
-    string(APPEND LEANSHARED_LINKER_FLAGS " -Wl,--out-implib,${CMAKE_BINARY_DIR}/lib/lean/libleanshared.dll.a")
-  endif()
+endif()
+
+if (${CMAKE_SYSTEM_NAME} MATCHES "Emscripten")
+  # We do not use dynamic linking via leanshared for Emscripten to keep things
+  # simple. (And we are not interested in `Lake` anyway.) To use dynamic
+  # linking, we would probably have to set MAIN_MODULE=2 on `leanshared`,
+  # SIDE_MODULE=2 on `lean`, and set CMAKE_SHARED_LIBRARY_SUFFIX to ".js".
+  string(APPEND LEAN_EXE_LINKER_FLAGS " ${TOOLCHAIN_STATIC_LINKER_FLAGS} ${EMSCRIPTEN_SETTINGS} -lnodefs.js -s EXIT_RUNTIME=1 -s MAIN_MODULE=1 -s LINKABLE=1 -s EXPORT_ALL=1")
 endif()
 
 # Build the compiler using the bootstrapped C sources for stage0, and use
@@ -520,10 +528,6 @@ if (LLVM AND ${STAGE} GREATER 0)
   set(EXTRA_LEANMAKE_OPTS "LLVM=1")
 endif()
 
-# Escape for `make`. Yes, twice.
-string(REPLACE "$" "$$" CMAKE_EXE_LINKER_FLAGS_MAKE "${CMAKE_EXE_LINKER_FLAGS}")
-string(REPLACE "$" "$$" CMAKE_EXE_LINKER_FLAGS_MAKE_MAKE "${CMAKE_EXE_LINKER_FLAGS_MAKE}")
-configure_file(${LEAN_SOURCE_DIR}/stdlib.make.in ${CMAKE_BINARY_DIR}/stdlib.make)
 add_custom_target(make_stdlib ALL
   WORKING_DIRECTORY ${LEAN_SOURCE_DIR}
   # The actual rule is in a separate makefile because we want to prefix it with '+' to use the Make job server
@@ -541,13 +545,33 @@ endif()
 # We declare these as separate custom targets so they use separate `make` invocations, which makes `make` recompute which dependencies
 # (e.g. `libLean.a`) are now newer than the target file
 
-add_custom_target(leanshared ALL
-  WORKING_DIRECTORY ${LEAN_SOURCE_DIR}
-  DEPENDS make_stdlib leancpp leanrt_initial-exec
-  COMMAND $(MAKE) -f ${CMAKE_BINARY_DIR}/stdlib.make leanshared
-  VERBATIM)
+if(${CMAKE_SYSTEM_NAME} MATCHES "Emscripten")
+  # dummy targets, see `MAIN_MODULE` discussion above
+  add_custom_target(Init_shared ALL
+    DEPENDS make_stdlib leanrt_initial-exec
+    COMMAND touch ${CMAKE_LIBRARY_OUTPUT_DIRECTORY}/libInit_shared${CMAKE_SHARED_LIBRARY_SUFFIX}
+  )
+  add_custom_target(leanshared ALL
+    DEPENDS Init_shared leancpp
+    COMMAND touch ${CMAKE_LIBRARY_OUTPUT_DIRECTORY}/libleanshared${CMAKE_SHARED_LIBRARY_SUFFIX}
+  )
+else()
+  add_custom_target(Init_shared ALL
+    WORKING_DIRECTORY ${LEAN_SOURCE_DIR}
+    DEPENDS make_stdlib leanrt_initial-exec
+    COMMAND $(MAKE) -f ${CMAKE_BINARY_DIR}/stdlib.make Init_shared
+    VERBATIM)
 
-if(${STAGE} GREATER 0)
+  add_custom_target(leanshared ALL
+    WORKING_DIRECTORY ${LEAN_SOURCE_DIR}
+    DEPENDS Init_shared leancpp
+    COMMAND $(MAKE) -f ${CMAKE_BINARY_DIR}/stdlib.make leanshared
+    VERBATIM)
+
+  string(APPEND CMAKE_EXE_LINKER_FLAGS " -lInit_shared -lleanshared")
+endif()
+
+if(${STAGE} GREATER 0 AND NOT ${CMAKE_SYSTEM_NAME} MATCHES "Emscripten")
   if(NOT EXISTS ${LEAN_SOURCE_DIR}/lake/Lake.lean)
     message(FATAL_ERROR "src/lake does not exist. Please check out the Lake submodule using `git submodule update --init src/lake`.")
   endif()
@@ -564,11 +588,15 @@ if(PREV_STAGE)
     COMMAND bash -c 'CSRCS=${CMAKE_BINARY_DIR}/lib/temp script/update-stage0'
     DEPENDS make_stdlib
     WORKING_DIRECTORY "${LEAN_SOURCE_DIR}/..")
+
+  add_custom_target(update-stage0-commit
+    COMMAND git commit -m "chore: update stage0"
+    DEPENDS update-stage0)
 endif()
 
 # use Bash version for building, use Lean version in bin/ for tests & distribution
 configure_file("${LEAN_SOURCE_DIR}/bin/leanc.in" "${CMAKE_BINARY_DIR}/leanc.sh" @ONLY)
-if(${STAGE} GREATER 0 AND EXISTS ${LEAN_SOURCE_DIR}/Leanc.lean)
+if(${STAGE} GREATER 0 AND EXISTS ${LEAN_SOURCE_DIR}/Leanc.lean AND NOT ${CMAKE_SYSTEM_NAME} MATCHES "Emscripten")
   configure_file("${LEAN_SOURCE_DIR}/Leanc.lean" "${CMAKE_BINARY_DIR}/leanc/Leanc.lean" @ONLY)
   add_custom_target(leanc ALL
     WORKING_DIRECTORY ${CMAKE_BINARY_DIR}/leanc
@@ -619,3 +647,8 @@ if(LEAN_INSTALL_PREFIX)
   set(LEAN_INSTALL_SUFFIX "-${LOWER_SYSTEM_NAME}" CACHE STRING "If LEAN_INSTALL_PREFIX is set, append this value to CMAKE_INSTALL_PREFIX")
   set(CMAKE_INSTALL_PREFIX "${LEAN_INSTALL_PREFIX}/lean-${LEAN_VERSION_STRING}${LEAN_INSTALL_SUFFIX}")
 endif()
+
+# Escape for `make`. Yes, twice.
+string(REPLACE "$" "$$" CMAKE_EXE_LINKER_FLAGS_MAKE "${CMAKE_EXE_LINKER_FLAGS}")
+string(REPLACE "$" "$$" CMAKE_EXE_LINKER_FLAGS_MAKE_MAKE "${CMAKE_EXE_LINKER_FLAGS_MAKE}")
+configure_file(${LEAN_SOURCE_DIR}/stdlib.make.in ${CMAKE_BINARY_DIR}/stdlib.make)

src/Init.lean

@@ -8,6 +8,7 @@ import Init.Prelude
 import Init.Notation
 import Init.Tactics
 import Init.TacticsExtra
+import Init.ByCases
 import Init.RCases
 import Init.Core
 import Init.Control
@@ -23,8 +24,13 @@ import Init.MetaTypes
 import Init.Meta
 import Init.NotationExtra
 import Init.SimpLemmas
+import Init.PropLemmas
 import Init.Hints
 import Init.Conv
 import Init.Guard
 import Init.Simproc
 import Init.SizeOfLemmas
+import Init.BinderPredicates
+import Init.Ext
+import Init.Omega
+import Init.MacroTrace

src/Init/BinderPredicates.lean

@@ -0,0 +1,82 @@
+/-
+Copyright (c) 2021 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Gabriel Ebner
+-/
+prelude
+import Init.NotationExtra
+
+namespace Lean
+
+/--
+The syntax category of binder predicates contains predicates like `> 0`, `∈ s`, etc.
+(`: t` should not be a binder predicate because it would clash with the built-in syntax for ∀/∃.)
+-/
+declare_syntax_cat binderPred
+
+/--
+`satisfies_binder_pred% t pred` expands to a proposition expressing that `t` satisfies `pred`.
+-/
+syntax "satisfies_binder_pred% " term:max binderPred : term
+
+-- Extend ∀ and ∃ to binder predicates.
+
+/--
+The notation `∃ x < 2, p x` is shorthand for `∃ x, x < 2 ∧ p x`,
+and similarly for other binary operators.
+-/
+syntax "∃ " binderIdent binderPred ", " term : term
+/--
+The notation `∀ x < 2, p x` is shorthand for `∀ x, x < 2 → p x`,
+and similarly for other binary operators.
+-/
+syntax "∀ " binderIdent binderPred ", " term : term
+
+macro_rules
+  | `(∃ $x:ident $pred:binderPred, $p) =>
+    `(∃ $x:ident, satisfies_binder_pred% $x $pred ∧ $p)
+  | `(∃ _ $pred:binderPred, $p) =>
+    `(∃ x, satisfies_binder_pred% x $pred ∧ $p)
+
+macro_rules
+  | `(∀ $x:ident $pred:binderPred, $p) =>
+    `(∀ $x:ident, satisfies_binder_pred% $x $pred → $p)
+  | `(∀ _ $pred:binderPred, $p) =>
+    `(∀ x, satisfies_binder_pred% x $pred → $p)
+
+/-- Declare `∃ x > y, ...` as syntax for `∃ x, x > y ∧ ...` -/
+binder_predicate x " > " y:term => `($x > $y)
+/-- Declare `∃ x ≥ y, ...` as syntax for `∃ x, x ≥ y ∧ ...` -/
+binder_predicate x " ≥ " y:term => `($x ≥ $y)
+/-- Declare `∃ x < y, ...` as syntax for `∃ x, x < y ∧ ...` -/
+binder_predicate x " < " y:term => `($x < $y)
+/-- Declare `∃ x ≤ y, ...` as syntax for `∃ x, x ≤ y ∧ ...` -/
+binder_predicate x " ≤ " y:term => `($x ≤ $y)
+/-- Declare `∃ x ≠ y, ...` as syntax for `∃ x, x ≠ y ∧ ...` -/
+binder_predicate x " ≠ " y:term => `($x ≠ $y)
+
+/-- Declare `∀ x ∈ y, ...` as syntax for `∀ x, x ∈ y → ...` and `∃ x ∈ y, ...` as syntax for
+`∃ x, x ∈ y ∧ ...` -/
+binder_predicate x " ∈ " y:term => `($x ∈ $y)
+
+/-- Declare `∀ x ∉ y, ...` as syntax for `∀ x, x ∉ y → ...` and `∃ x ∉ y, ...` as syntax for
+`∃ x, x ∉ y ∧ ...` -/
+binder_predicate x " ∉ " y:term => `($x ∉ $y)
+
+/-- Declare `∀ x ⊆ y, ...` as syntax for `∀ x, x ⊆ y → ...` and `∃ x ⊆ y, ...` as syntax for
+`∃ x, x ⊆ y ∧ ...` -/
+binder_predicate x " ⊆ " y:term => `($x ⊆ $y)
+
+/-- Declare `∀ x ⊂ y, ...` as syntax for `∀ x, x ⊂ y → ...` and `∃ x ⊂ y, ...` as syntax for
+`∃ x, x ⊂ y ∧ ...` -/
+binder_predicate x " ⊂ " y:term => `($x ⊂ $y)
+
+/-- Declare `∀ x ⊇ y, ...` as syntax for `∀ x, x ⊇ y → ...` and `∃ x ⊇ y, ...` as syntax for
+`∃ x, x ⊇ y ∧ ...` -/
+binder_predicate x " ⊇ " y:term => `($x ⊇ $y)
+
+/-- Declare `∀ x ⊃ y, ...` as syntax for `∀ x, x ⊃ y → ...` and `∃ x ⊃ y, ...` as syntax for
+`∃ x, x ⊃ y ∧ ...` -/
+binder_predicate x " ⊃ " y:term => `($x ⊃ $y)
+
+end Lean

src/Init/ByCases.lean

@@ -0,0 +1,65 @@
+/-
+Copyright (c) 2024 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Leonardo de Moura, Mario Carneiro
+-/
+prelude
+import Init.Classical
+
+/-! # by_cases tactic and if-then-else support -/
+
+/--
+`by_cases (h :)? p` splits the main goal into two cases, assuming `h : p` in the first branch, and `h : ¬ p` in the second branch.
+-/
+syntax "by_cases " (atomic(ident " : "))? term : tactic
+
+macro_rules
+  | `(tactic| by_cases $e) => `(tactic| by_cases h : $e)
+macro_rules
+  | `(tactic| by_cases $h : $e) =>
+    `(tactic| open Classical in refine if $h:ident : $e then ?pos else ?neg)
+
+/-! ## if-then-else -/
+
+@[simp] theorem if_true {_ : Decidable True} (t e : α) : ite True t e = t := if_pos trivial
+
+@[simp] theorem if_false {_ : Decidable False} (t e : α) : ite False t e = e := if_neg id
+
+theorem ite_id [Decidable c] {α} (t : α) : (if c then t else t) = t := by split <;> rfl
+
+/-- A function applied to a `dite` is a `dite` of that function applied to each of the branches. -/
+theorem apply_dite (f : α → β) (P : Prop) [Decidable P] (x : P → α) (y : ¬P → α) :
+    f (dite P x y) = dite P (fun h => f (x h)) (fun h => f (y h)) := by
+  by_cases h : P <;> simp [h]
+
+/-- A function applied to a `ite` is a `ite` of that function applied to each of the branches. -/
+theorem apply_ite (f : α → β) (P : Prop) [Decidable P] (x y : α) :
+    f (ite P x y) = ite P (f x) (f y) :=
+  apply_dite f P (fun _ => x) (fun _ => y)
+
+@[simp] theorem dite_eq_left_iff {P : Prop} [Decidable P] {B : ¬ P → α} :
+    dite P (fun _ => a) B = a ↔ ∀ h, B h = a := by
+  by_cases P <;> simp [*, forall_prop_of_true, forall_prop_of_false]
+
+@[simp] theorem dite_eq_right_iff {P : Prop} [Decidable P] {A : P → α} :
+    (dite P A fun _ => b) = b ↔ ∀ h, A h = b := by
+  by_cases P <;> simp [*, forall_prop_of_true, forall_prop_of_false]
+
+@[simp] theorem ite_eq_left_iff {P : Prop} [Decidable P] : ite P a b = a ↔ ¬P → b = a :=
+  dite_eq_left_iff
+
+@[simp] theorem ite_eq_right_iff {P : Prop} [Decidable P] : ite P a b = b ↔ P → a = b :=
+  dite_eq_right_iff
+
+/-- A `dite` whose results do not actually depend on the condition may be reduced to an `ite`. -/
+@[simp] theorem dite_eq_ite [Decidable P] : (dite P (fun _ => a) fun _ => b) = ite P a b := rfl
+
+-- We don't mark this as `simp` as it is already handled by `ite_eq_right_iff`.
+theorem ite_some_none_eq_none [Decidable P] :
+    (if P then some x else none) = none ↔ ¬ P := by
+  simp only [ite_eq_right_iff]
+  rfl
+
+@[simp] theorem ite_some_none_eq_some [Decidable P] :
+    (if P then some x else none) = some y ↔ P ∧ x = y := by
+  split <;> simp_all

src/Init/Classical.lean

@@ -4,8 +4,7 @@ Released under Apache 2.0 license as described in the file LICENSE.
 Authors: Leonardo de Moura, Mario Carneiro
 -/
 prelude
-import Init.Core
-import Init.NotationExtra
+import Init.PropLemmas
 
 universe u v
 
@@ -112,8 +111,8 @@ theorem skolem {α : Sort u} {b : α → Sort v} {p : ∀ x, b x → Prop} : (
 
 theorem propComplete (a : Prop) : a = True ∨ a = False :=
   match em a with
-  | Or.inl ha => Or.inl (propext (Iff.intro (fun _ => ⟨⟩) (fun _ => ha)))
-  | Or.inr hn => Or.inr (propext (Iff.intro (fun h => hn h) (fun h => False.elim h)))
+  | Or.inl ha => Or.inl (eq_true ha)
+  | Or.inr hn => Or.inr (eq_false hn)
 
 -- this supercedes byCases in Decidable
 theorem byCases {p q : Prop} (hpq : p → q) (hnpq : ¬p → q) : q :=
@@ -123,15 +122,49 @@ theorem byCases {p q : Prop} (hpq : p → q) (hnpq : ¬p → q) : q :=
 theorem byContradiction {p : Prop} (h : ¬p → False) : p :=
   Decidable.byContradiction (dec := propDecidable _) h
 
+/-- The Double Negation Theorem: `¬¬P` is equivalent to `P`.
+The left-to-right direction, double negation elimination (DNE),
+is classically true but not constructively. -/
+@[simp] theorem not_not : ¬¬a ↔ a := Decidable.not_not
+
+@[simp low] theorem not_forall {p : α → Prop} : (¬∀ x, p x) ↔ ∃ x, ¬p x := Decidable.not_forall
+
+theorem not_forall_not {p : α → Prop} : (¬∀ x, ¬p x) ↔ ∃ x, p x := Decidable.not_forall_not
+theorem not_exists_not {p : α → Prop} : (¬∃ x, ¬p x) ↔ ∀ x, p x := Decidable.not_exists_not
+
+theorem forall_or_exists_not (P : α → Prop) : (∀ a, P a) ∨ ∃ a, ¬ P a := by
+  rw [← not_forall]; exact em _
+theorem exists_or_forall_not (P : α → Prop) : (∃ a, P a) ∨ ∀ a, ¬ P a := by
+  rw [← not_exists]; exact em _
+
+theorem or_iff_not_imp_left  : a ∨ b ↔ (¬a → b) := Decidable.or_iff_not_imp_left
+theorem or_iff_not_imp_right : a ∨ b ↔ (¬b → a) := Decidable.or_iff_not_imp_right
+
+theorem not_imp_iff_and_not : ¬(a → b) ↔ a ∧ ¬b := Decidable.not_imp_iff_and_not
+
+theorem not_and_iff_or_not_not : ¬(a ∧ b) ↔ ¬a ∨ ¬b := Decidable.not_and_iff_or_not_not
+
+theorem not_iff : ¬(a ↔ b) ↔ (¬a ↔ b) := Decidable.not_iff
+
+@[simp] theorem imp_iff_left_iff  : (b ↔ a → b) ↔ a ∨ b := Decidable.imp_iff_left_iff
+@[simp] theorem imp_iff_right_iff : (a → b ↔ b) ↔ a ∨ b := Decidable.imp_iff_right_iff
+
+@[simp] theorem and_or_imp : a ∧ b ∨ (a → c) ↔ a → b ∨ c := Decidable.and_or_imp
+
+@[simp] theorem not_imp : ¬(a → b) ↔ a ∧ ¬b := Decidable.not_imp_iff_and_not
+
+@[simp] theorem imp_and_neg_imp_iff (p q : Prop) : (p → q) ∧ (¬p → q) ↔ q :=
+  Iff.intro (fun (a : _ ∧ _) => (Classical.em p).rec a.left a.right)
+            (fun a => And.intro (fun _ => a) (fun _ => a))
+
 end Classical
 
-/--
-`by_cases (h :)? p` splits the main goal into two cases, assuming `h : p` in the first branch, and `h : ¬ p` in the second branch.
--/
-syntax "by_cases " (atomic(ident " : "))? term : tactic
+/- Export for Mathlib compat. -/
+export Classical (imp_iff_right_iff imp_and_neg_imp_iff and_or_imp not_imp)
 
-macro_rules
-  | `(tactic| by_cases $e) => `(tactic| by_cases h : $e)
-macro_rules
-  | `(tactic| by_cases $h : $e) =>
-    `(tactic| open Classical in refine if $h:ident : $e then ?pos else ?neg)
+/-- Extract an element from a existential statement, using `Classical.choose`. -/
+-- This enables projection notation.
+@[reducible] noncomputable def Exists.choose {p : α → Prop} (P : ∃ a, p a) : α := Classical.choose P
+
+/-- Show that an element extracted from `P : ∃ a, p a` using `P.choose` satisfies `p`. -/
+theorem Exists.choose_spec {p : α → Prop} (P : ∃ a, p a) : p P.choose := Classical.choose_spec P

src/Init/Coe.lean

@@ -321,7 +321,7 @@ Helper definition used by the elaborator. It is not meant to be used directly by
 This is used for coercions between monads, in the case where we want to apply
 a monad lift and a coercion on the result type at the same time.
 -/
-@[inline, coe_decl] def Lean.Internal.liftCoeM {m : Type u → Type v} {n : Type u → Type w} {α β : Type u}
+@[coe_decl] abbrev Lean.Internal.liftCoeM {m : Type u → Type v} {n : Type u → Type w} {α β : Type u}
     [MonadLiftT m n] [∀ a, CoeT α a β] [Monad n] (x : m α) : n β := do
   let a ← liftM x
   pure (CoeT.coe a)
@@ -331,7 +331,7 @@ Helper definition used by the elaborator. It is not meant to be used directly by
 
 This is used for coercing the result type under a monad.
 -/
-@[inline, coe_decl] def Lean.Internal.coeM {m : Type u → Type v} {α β : Type u}
+@[coe_decl] abbrev Lean.Internal.coeM {m : Type u → Type v} {α β : Type u}
     [∀ a, CoeT α a β] [Monad m] (x : m α) : m β := do
   let a ← x
   pure (CoeT.coe a)

src/Init/Control/Basic.lean

@@ -20,8 +20,29 @@ def Functor.discard {f : Type u → Type v} {α : Type u} [Functor f] (x : f α)
 
 export Functor (discard)
 
+/--
+An `Alternative` functor is an `Applicative` functor that can "fail" or be "empty"
+and a binary operation `<|>` that “collects values” or finds the “left-most success”.
+
+Important instances include
+* `Option`, where `failure := none` and `<|>` returns the left-most `some`.
+* Parser combinators typically provide an `Applicative` instance for error-handling and
+  backtracking.
+  
+Error recovery and state can interact subtly. For example, the implementation of `Alternative` for `OptionT (StateT σ Id)` keeps modifications made to the state while recovering from failure, while `StateT σ (OptionT Id)` discards them.
+-/
+-- NB: List instance is in mathlib. Once upstreamed, add
+-- * `List`, where `failure` is the empty list and `<|>` concatenates.
 class Alternative (f : Type u → Type v) extends Applicative f : Type (max (u+1) v) where
+  /--
+  Produces an empty collection or recoverable failure.  The `<|>` operator collects values or recovers
+  from failures. See `Alternative` for more details.
+  -/
   failure : {α : Type u} → f α
+  /--
+  Depending on the `Alternative` instance, collects values or recovers from `failure`s by
+  returning the leftmost success. Can be written using the `<|>` operator syntax.
+  -/
   orElse  : {α : Type u} → f α → (Unit → f α) → f α
 
 instance (f : Type u → Type v) (α : Type u) [Alternative f] : OrElse (f α) := ⟨Alternative.orElse⟩
@@ -30,9 +51,15 @@ variable {f : Type u → Type v} [Alternative f] {α : Type u}
 
 export Alternative (failure)
 
+/--
+If the proposition `p` is true, does nothing, else fails (using `failure`).
+-/
 @[always_inline, inline] def guard {f : Type → Type v} [Alternative f] (p : Prop) [Decidable p] : f Unit :=
   if p then pure () else failure
 
+/--
+Returns `some x` if `f` succeeds with value `x`, else returns `none`.
+-/
 @[always_inline, inline] def optional (x : f α) : f (Option α) :=
   some <$> x <|> pure none
 

src/Init/Control/ExceptCps.lean

@@ -4,7 +4,7 @@ Released under Apache 2.0 license as described in the file LICENSE.
 Authors: Leonardo de Moura
 -/
 prelude
-import Init.Control.Lawful
+import Init.Control.Lawful.Basic
 
 /-!
 The Exception monad transformer using CPS style.
@@ -18,6 +18,7 @@ namespace ExceptCpsT
 def run {ε α : Type u} [Monad m] (x : ExceptCpsT ε m α) : m (Except ε α) :=
   x _ (fun a => pure (Except.ok a)) (fun e => pure (Except.error e))
 
+set_option linter.unusedVariables false in  -- `s` unused
 @[always_inline, inline]
 def runK {ε α : Type u} (x : ExceptCpsT ε m α) (s : ε) (ok : α → m β) (error : ε → m β) : m β :=
   x _ ok error

src/Init/Control/Lawful.lean

@@ -1,309 +1,8 @@
 /-
 Copyright (c) 2021 Microsoft Corporation. All rights reserved.
 Released under Apache 2.0 license as described in the file LICENSE.
-Authors: Sebastian Ullrich, Leonardo de Moura
+Authors: Sebastian Ullrich, Leonardo de Moura, Mario Carneiro
 -/
 prelude
-import Init.SimpLemmas
-import Init.Control.Except
-import Init.Control.StateRef
-
-open Function
-
-@[simp] theorem monadLift_self [Monad m] (x : m α) : monadLift x = x :=
-  rfl
-
-class LawfulFunctor (f : Type u → Type v) [Functor f] : Prop where
-  map_const          : (Functor.mapConst : α → f β → f α) = Functor.map ∘ const β
-  id_map   (x : f α) : id <$> x = x
-  comp_map (g : α → β) (h : β → γ) (x : f α) : (h ∘ g) <$> x = h <$> g <$> x
-
-export LawfulFunctor (map_const id_map comp_map)
-
-attribute [simp] id_map
-
-@[simp] theorem id_map' [Functor m] [LawfulFunctor m] (x : m α) : (fun a => a) <$> x = x :=
-  id_map x
-
-class LawfulApplicative (f : Type u → Type v) [Applicative f] extends LawfulFunctor f : Prop where
-  seqLeft_eq  (x : f α) (y : f β)     : x <* y = const β <$> x <*> y
-  seqRight_eq (x : f α) (y : f β)     : x *> y = const α id <$> x <*> y
-  pure_seq    (g : α → β) (x : f α)   : pure g <*> x = g <$> x
-  map_pure    (g : α → β) (x : α)     : g <$> (pure x : f α) = pure (g x)
-  seq_pure    {α β : Type u} (g : f (α → β)) (x : α) : g <*> pure x = (fun h => h x) <$> g
-  seq_assoc   {α β γ : Type u} (x : f α) (g : f (α → β)) (h : f (β → γ)) : h <*> (g <*> x) = ((@comp α β γ) <$> h) <*> g <*> x
-  comp_map g h x := (by
-    repeat rw [← pure_seq]
-    simp [seq_assoc, map_pure, seq_pure])
-
-export LawfulApplicative (seqLeft_eq seqRight_eq pure_seq map_pure seq_pure seq_assoc)
-
-attribute [simp] map_pure seq_pure
-
-@[simp] theorem pure_id_seq [Applicative f] [LawfulApplicative f] (x : f α) : pure id <*> x = x := by
-  simp [pure_seq]
-
-class LawfulMonad (m : Type u → Type v) [Monad m] extends LawfulApplicative m : Prop where
-  bind_pure_comp (f : α → β) (x : m α) : x >>= (fun a => pure (f a)) = f <$> x
-  bind_map       {α β : Type u} (f : m (α → β)) (x : m α) : f >>= (. <$> x) = f <*> x
-  pure_bind      (x : α) (f : α → m β) : pure x >>= f = f x
-  bind_assoc     (x : m α) (f : α → m β) (g : β → m γ) : x >>= f >>= g = x >>= fun x => f x >>= g
-  map_pure g x    := (by rw [← bind_pure_comp, pure_bind])
-  seq_pure g x    := (by rw [← bind_map]; simp [map_pure, bind_pure_comp])
-  seq_assoc x g h := (by simp [← bind_pure_comp, ← bind_map, bind_assoc, pure_bind])
-
-export LawfulMonad (bind_pure_comp bind_map pure_bind bind_assoc)
-attribute [simp] pure_bind bind_assoc
-
-@[simp] theorem bind_pure [Monad m] [LawfulMonad m] (x : m α) : x >>= pure = x := by
-  show x >>= (fun a => pure (id a)) = x
-  rw [bind_pure_comp, id_map]
-
-theorem map_eq_pure_bind [Monad m] [LawfulMonad m] (f : α → β) (x : m α) : f <$> x = x >>= fun a => pure (f a) := by
-  rw [← bind_pure_comp]
-
-theorem seq_eq_bind_map {α β : Type u} [Monad m] [LawfulMonad m] (f : m (α → β)) (x : m α) : f <*> x = f >>= (. <$> x) := by
-  rw [← bind_map]
-
-theorem bind_congr [Bind m] {x : m α} {f g : α → m β} (h : ∀ a, f a = g a) : x >>= f = x >>= g := by
-  simp [funext h]
-
-@[simp] theorem bind_pure_unit [Monad m] [LawfulMonad m] {x : m PUnit} : (x >>= fun _ => pure ⟨⟩) = x := by
-  rw [bind_pure]
-
-theorem map_congr [Functor m] {x : m α} {f g : α → β} (h : ∀ a, f a = g a) : (f <$> x : m β) = g <$> x := by
-  simp [funext h]
-
-theorem seq_eq_bind {α β : Type u} [Monad m] [LawfulMonad m] (mf : m (α → β)) (x : m α) : mf <*> x = mf >>= fun f => f <$> x := by
-  rw [bind_map]
-
-theorem seqRight_eq_bind [Monad m] [LawfulMonad m] (x : m α) (y : m β) : x *> y = x >>= fun _ => y := by
-  rw [seqRight_eq]
-  simp [map_eq_pure_bind, seq_eq_bind_map, const]
-
-theorem seqLeft_eq_bind [Monad m] [LawfulMonad m] (x : m α) (y : m β) : x <* y = x >>= fun a => y >>= fun _ => pure a := by
-  rw [seqLeft_eq]; simp [map_eq_pure_bind, seq_eq_bind_map]
-
-/-! # Id -/
-
-namespace Id
-
-@[simp] theorem map_eq (x : Id α) (f : α → β) : f <$> x = f x := rfl
-@[simp] theorem bind_eq (x : Id α) (f : α → id β) : x >>= f = f x := rfl
-@[simp] theorem pure_eq (a : α) : (pure a : Id α) = a := rfl
-
-instance : LawfulMonad Id := by
-  refine' { .. } <;> intros <;> rfl
-
-end Id
-
-/-! # ExceptT -/
-
-namespace ExceptT
-
-theorem ext [Monad m] {x y : ExceptT ε m α} (h : x.run = y.run) : x = y := by
-  simp [run] at h
-  assumption
-
-@[simp] theorem run_pure [Monad m] (x : α) : run (pure x : ExceptT ε m α) = pure (Except.ok x) := rfl
-
-@[simp] theorem run_lift  [Monad.{u, v} m] (x : m α) : run (ExceptT.lift x : ExceptT ε m α) = (Except.ok <$> x : m (Except ε α)) := rfl
-
-@[simp] theorem run_throw [Monad m] : run (throw e : ExceptT ε m β) = pure (Except.error e) := rfl
-
-@[simp] theorem run_bind_lift [Monad m] [LawfulMonad m] (x : m α) (f : α → ExceptT ε m β) : run (ExceptT.lift x >>= f : ExceptT ε m β) = x >>= fun a => run (f a) := by
-  simp[ExceptT.run, ExceptT.lift, bind, ExceptT.bind, ExceptT.mk, ExceptT.bindCont, map_eq_pure_bind]
-
-@[simp] theorem bind_throw [Monad m] [LawfulMonad m] (f : α → ExceptT ε m β) : (throw e >>= f) = throw e := by
-  simp [throw, throwThe, MonadExceptOf.throw, bind, ExceptT.bind, ExceptT.bindCont, ExceptT.mk]
-
-theorem run_bind [Monad m] (x : ExceptT ε m α)
-        : run (x >>= f : ExceptT ε m β)
-          =
-          run x >>= fun
-                     | Except.ok x => run (f x)
-                     | Except.error e => pure (Except.error e) :=
-  rfl
-
-@[simp] theorem lift_pure [Monad m] [LawfulMonad m] (a : α) : ExceptT.lift (pure a) = (pure a : ExceptT ε m α) := by
-  simp [ExceptT.lift, pure, ExceptT.pure]
-
-@[simp] theorem run_map [Monad m] [LawfulMonad m] (f : α → β) (x : ExceptT ε m α)
-    : (f <$> x).run = Except.map f <$> x.run := by
-  simp [Functor.map, ExceptT.map, map_eq_pure_bind]
-  apply bind_congr
-  intro a; cases a <;> simp [Except.map]
-
-protected theorem seq_eq {α β ε : Type u} [Monad m] (mf : ExceptT ε m (α → β)) (x : ExceptT ε m α) : mf <*> x = mf >>= fun f => f <$> x :=
-  rfl
-
-protected theorem bind_pure_comp [Monad m] [LawfulMonad m] (f : α → β) (x : ExceptT ε m α) : x >>= pure ∘ f = f <$> x := by
-  intros; rfl
-
-protected theorem seqLeft_eq {α β ε : Type u} {m : Type u → Type v} [Monad m] [LawfulMonad m] (x : ExceptT ε m α) (y : ExceptT ε m β) : x <* y = const β <$> x <*> y := by
-  show (x >>= fun a => y >>= fun _ => pure a) = (const (α := α) β <$> x) >>= fun f => f <$> y
-  rw [← ExceptT.bind_pure_comp]
-  apply ext
-  simp [run_bind]
-  apply bind_congr
-  intro
-  | Except.error _ => simp
-  | Except.ok _ =>
-    simp [map_eq_pure_bind]; apply bind_congr; intro b;
-    cases b <;> simp [comp, Except.map, const]
-
-protected theorem seqRight_eq [Monad m] [LawfulMonad m] (x : ExceptT ε m α) (y : ExceptT ε m β) : x *> y = const α id <$> x <*> y := by
-  show (x >>= fun _ => y) = (const α id <$> x) >>= fun f => f <$> y
-  rw [← ExceptT.bind_pure_comp]
-  apply ext
-  simp [run_bind]
-  apply bind_congr
-  intro a; cases a <;> simp
-
-instance [Monad m] [LawfulMonad m] : LawfulMonad (ExceptT ε m) where
-  id_map         := by intros; apply ext; simp
-  map_const      := by intros; rfl
-  seqLeft_eq     := ExceptT.seqLeft_eq
-  seqRight_eq    := ExceptT.seqRight_eq
-  pure_seq       := by intros; apply ext; simp [ExceptT.seq_eq, run_bind]
-  bind_pure_comp := ExceptT.bind_pure_comp
-  bind_map       := by intros; rfl
-  pure_bind      := by intros; apply ext; simp [run_bind]
-  bind_assoc     := by intros; apply ext; simp [run_bind]; apply bind_congr; intro a; cases a <;> simp
-
-end ExceptT
-
-/-! # ReaderT -/
-
-namespace ReaderT
-
-theorem ext {x y : ReaderT ρ m α} (h : ∀ ctx, x.run ctx = y.run ctx) : x = y := by
-  simp [run] at h
-  exact funext h
-
-@[simp] theorem run_pure [Monad m] (a : α) (ctx : ρ) : (pure a : ReaderT ρ m α).run ctx = pure a := rfl
-
-@[simp] theorem run_bind [Monad m] (x : ReaderT ρ m α) (f : α → ReaderT ρ m β) (ctx : ρ)
-    : (x >>= f).run ctx = x.run ctx >>= λ a => (f a).run ctx := rfl
-
-@[simp] theorem run_mapConst [Monad m] (a : α) (x : ReaderT ρ m β) (ctx : ρ)
-    : (Functor.mapConst a x).run ctx = Functor.mapConst a (x.run ctx) := rfl
-
-@[simp] theorem run_map [Monad m] (f : α → β) (x : ReaderT ρ m α) (ctx : ρ)
-    : (f <$> x).run ctx = f <$> x.run ctx := rfl
-
-@[simp] theorem run_monadLift [MonadLiftT n m] (x : n α) (ctx : ρ)
-    : (monadLift x : ReaderT ρ m α).run ctx = (monadLift x : m α) := rfl
-
-@[simp] theorem run_monadMap [MonadFunctor n m] (f : {β : Type u} → n β → n β) (x : ReaderT ρ m α) (ctx : ρ)
-    : (monadMap @f x : ReaderT ρ m α).run ctx = monadMap @f (x.run ctx) := rfl
-
-@[simp] theorem run_read [Monad m] (ctx : ρ) : (ReaderT.read : ReaderT ρ m ρ).run ctx = pure ctx := rfl
-
-@[simp] theorem run_seq {α β : Type u} [Monad m] (f : ReaderT ρ m (α → β)) (x : ReaderT ρ m α) (ctx : ρ)
-    : (f <*> x).run ctx = (f.run ctx <*> x.run ctx) := rfl
-
-@[simp] theorem run_seqRight [Monad m] (x : ReaderT ρ m α) (y : ReaderT ρ m β) (ctx : ρ)
-    : (x *> y).run ctx = (x.run ctx *> y.run ctx) := rfl
-
-@[simp] theorem run_seqLeft [Monad m] (x : ReaderT ρ m α) (y : ReaderT ρ m β) (ctx : ρ)
-    : (x <* y).run ctx = (x.run ctx <* y.run ctx) := rfl
-
-instance [Monad m] [LawfulFunctor m] : LawfulFunctor (ReaderT ρ m) where
-  id_map    := by intros; apply ext; simp
-  map_const := by intros; funext a b; apply ext; intros; simp [map_const]
-  comp_map  := by intros; apply ext; intros; simp [comp_map]
-
-instance [Monad m] [LawfulApplicative m] : LawfulApplicative (ReaderT ρ m) where
-  seqLeft_eq  := by intros; apply ext; intros; simp [seqLeft_eq]
-  seqRight_eq := by intros; apply ext; intros; simp [seqRight_eq]
-  pure_seq    := by intros; apply ext; intros; simp [pure_seq]
-  map_pure    := by intros; apply ext; intros; simp [map_pure]
-  seq_pure    := by intros; apply ext; intros; simp [seq_pure]
-  seq_assoc   := by intros; apply ext; intros; simp [seq_assoc]
-
-instance [Monad m] [LawfulMonad m] : LawfulMonad (ReaderT ρ m) where
-  bind_pure_comp := by intros; apply ext; intros; simp [LawfulMonad.bind_pure_comp]
-  bind_map       := by intros; apply ext; intros; simp [bind_map]
-  pure_bind      := by intros; apply ext; intros; simp
-  bind_assoc     := by intros; apply ext; intros; simp
-
-end ReaderT
-
-/-! # StateRefT -/
-
-instance [Monad m] [LawfulMonad m] : LawfulMonad (StateRefT' ω σ m) :=
-  inferInstanceAs (LawfulMonad (ReaderT (ST.Ref ω σ) m))
-
-/-! # StateT -/
-
-namespace StateT
-
-theorem ext {x y : StateT σ m α} (h : ∀ s, x.run s = y.run s) : x = y :=
-  funext h
-
-@[simp] theorem run'_eq [Monad m] (x : StateT σ m α) (s : σ) : run' x s = (·.1) <$> run x s :=
-  rfl
-
-@[simp] theorem run_pure [Monad m] (a : α) (s : σ) : (pure a : StateT σ m α).run s = pure (a, s) := rfl
-
-@[simp] theorem run_bind [Monad m] (x : StateT σ m α) (f : α → StateT σ m β) (s : σ)
-    : (x >>= f).run s = x.run s >>= λ p => (f p.1).run p.2 := by
-  simp [bind, StateT.bind, run]
-
-@[simp] theorem run_map {α β σ : Type u} [Monad m] [LawfulMonad m] (f : α → β) (x : StateT σ m α) (s : σ) : (f <$> x).run s = (fun (p : α × σ) => (f p.1, p.2)) <$> x.run s := by
-  simp [Functor.map, StateT.map, run, map_eq_pure_bind]
-
-@[simp] theorem run_get [Monad m] (s : σ)    : (get : StateT σ m σ).run s = pure (s, s) := rfl
-
-@[simp] theorem run_set [Monad m] (s s' : σ) : (set s' : StateT σ m PUnit).run s = pure (⟨⟩, s') := rfl
-
-@[simp] theorem run_modify [Monad m] (f : σ → σ) (s : σ) : (modify f : StateT σ m PUnit).run s = pure (⟨⟩, f s) := rfl
-
-@[simp] theorem run_modifyGet [Monad m] (f : σ → α × σ) (s : σ) : (modifyGet f : StateT σ m α).run s = pure ((f s).1, (f s).2) := by
-  simp [modifyGet, MonadStateOf.modifyGet, StateT.modifyGet, run]
-
-@[simp] theorem run_lift {α σ : Type u} [Monad m] (x : m α) (s : σ) : (StateT.lift x : StateT σ m α).run s = x >>= fun a => pure (a, s) := rfl
-
-@[simp] theorem run_bind_lift {α σ : Type u} [Monad m] [LawfulMonad m] (x : m α) (f : α → StateT σ m β) (s : σ) : (StateT.lift x >>= f).run s = x >>= fun a => (f a).run s := by
-  simp [StateT.lift, StateT.run, bind, StateT.bind]
-
-@[simp] theorem run_monadLift {α σ : Type u} [Monad m] [MonadLiftT n m] (x : n α) (s : σ) : (monadLift x : StateT σ m α).run s = (monadLift x : m α) >>= fun a => pure (a, s) := rfl
-
-@[simp] theorem run_monadMap [Monad m] [MonadFunctor n m] (f : {β : Type u} → n β → n β) (x : StateT σ m α) (s : σ)
-    : (monadMap @f x : StateT σ m α).run s = monadMap @f (x.run s) := rfl
-
-@[simp] theorem run_seq {α β σ : Type u} [Monad m] [LawfulMonad m] (f : StateT σ m (α → β)) (x : StateT σ m α) (s : σ) : (f <*> x).run s = (f.run s >>= fun fs => (fun (p : α × σ) => (fs.1 p.1, p.2)) <$> x.run fs.2) := by
-  show (f >>= fun g => g <$> x).run s = _
-  simp
-
-@[simp] theorem run_seqRight [Monad m] [LawfulMonad m] (x : StateT σ m α) (y : StateT σ m β) (s : σ) : (x *> y).run s = (x.run s >>= fun p => y.run p.2) := by
-  show (x >>= fun _ => y).run s = _
-  simp
-
-@[simp] theorem run_seqLeft {α β σ : Type u} [Monad m] [LawfulMonad m] (x : StateT σ m α) (y : StateT σ m β) (s : σ) : (x <* y).run s = (x.run s >>= fun p => y.run p.2 >>= fun p' => pure (p.1, p'.2)) := by
-  show (x >>= fun a => y >>= fun _ => pure a).run s = _
-  simp
-
-theorem seqRight_eq [Monad m] [LawfulMonad m] (x : StateT σ m α) (y : StateT σ m β) : x *> y = const α id <$> x <*> y := by
-  apply ext; intro s
-  simp [map_eq_pure_bind, const]
-  apply bind_congr; intro p; cases p
-  simp [Prod.eta]
-
-theorem seqLeft_eq [Monad m] [LawfulMonad m] (x : StateT σ m α) (y : StateT σ m β) : x <* y = const β <$> x <*> y := by
-  apply ext; intro s
-  simp [map_eq_pure_bind]
-
-instance [Monad m] [LawfulMonad m] : LawfulMonad (StateT σ m) where
-  id_map         := by intros; apply ext; intros; simp[Prod.eta]
-  map_const      := by intros; rfl
-  seqLeft_eq     := seqLeft_eq
-  seqRight_eq    := seqRight_eq
-  pure_seq       := by intros; apply ext; intros; simp
-  bind_pure_comp := by intros; apply ext; intros; simp; apply LawfulMonad.bind_pure_comp
-  bind_map       := by intros; rfl
-  pure_bind      := by intros; apply ext; intros; simp
-  bind_assoc     := by intros; apply ext; intros; simp
-
-end StateT
+import Init.Control.Lawful.Basic
+import Init.Control.Lawful.Instances

src/Init/Control/Lawful/Basic.lean

@@ -0,0 +1,169 @@
+/-
+Copyright (c) 2021 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Sebastian Ullrich, Leonardo de Moura, Mario Carneiro
+-/
+prelude
+import Init.SimpLemmas
+import Init.Meta
+
+open Function
+
+@[simp] theorem monadLift_self [Monad m] (x : m α) : monadLift x = x :=
+  rfl
+
+/--
+The `Functor` typeclass only contains the operations of a functor.
+`LawfulFunctor` further asserts that these operations satisfy the laws of a functor,
+including the preservation of the identity and composition laws:
+```
+id <$> x = x
+(h ∘ g) <$> x = h <$> g <$> x
+```
+-/
+class LawfulFunctor (f : Type u → Type v) [Functor f] : Prop where
+  map_const          : (Functor.mapConst : α → f β → f α) = Functor.map ∘ const β
+  id_map   (x : f α) : id <$> x = x
+  comp_map (g : α → β) (h : β → γ) (x : f α) : (h ∘ g) <$> x = h <$> g <$> x
+
+export LawfulFunctor (map_const id_map comp_map)
+
+attribute [simp] id_map
+
+@[simp] theorem id_map' [Functor m] [LawfulFunctor m] (x : m α) : (fun a => a) <$> x = x :=
+  id_map x
+
+/--
+The `Applicative` typeclass only contains the operations of an applicative functor.
+`LawfulApplicative` further asserts that these operations satisfy the laws of an applicative functor:
+```
+pure id <*> v = v
+pure (·∘·) <*> u <*> v <*> w = u <*> (v <*> w)
+pure f <*> pure x = pure (f x)
+u <*> pure y = pure (· y) <*> u
+```
+-/
+class LawfulApplicative (f : Type u → Type v) [Applicative f] extends LawfulFunctor f : Prop where
+  seqLeft_eq  (x : f α) (y : f β)     : x <* y = const β <$> x <*> y
+  seqRight_eq (x : f α) (y : f β)     : x *> y = const α id <$> x <*> y
+  pure_seq    (g : α → β) (x : f α)   : pure g <*> x = g <$> x
+  map_pure    (g : α → β) (x : α)     : g <$> (pure x : f α) = pure (g x)
+  seq_pure    {α β : Type u} (g : f (α → β)) (x : α) : g <*> pure x = (fun h => h x) <$> g
+  seq_assoc   {α β γ : Type u} (x : f α) (g : f (α → β)) (h : f (β → γ)) : h <*> (g <*> x) = ((@comp α β γ) <$> h) <*> g <*> x
+  comp_map g h x := (by
+    repeat rw [← pure_seq]
+    simp [seq_assoc, map_pure, seq_pure])
+
+export LawfulApplicative (seqLeft_eq seqRight_eq pure_seq map_pure seq_pure seq_assoc)
+
+attribute [simp] map_pure seq_pure
+
+@[simp] theorem pure_id_seq [Applicative f] [LawfulApplicative f] (x : f α) : pure id <*> x = x := by
+  simp [pure_seq]
+
+/--
+The `Monad` typeclass only contains the operations of a monad.
+`LawfulMonad` further asserts that these operations satisfy the laws of a monad,
+including associativity and identity laws for `bind`:
+```
+pure x >>= f = f x
+x >>= pure = x
+x >>= f >>= g = x >>= (fun x => f x >>= g)
+```
+
+`LawfulMonad.mk'` is an alternative constructor containing useful defaults for many fields.
+-/
+class LawfulMonad (m : Type u → Type v) [Monad m] extends LawfulApplicative m : Prop where
+  bind_pure_comp (f : α → β) (x : m α) : x >>= (fun a => pure (f a)) = f <$> x
+  bind_map       {α β : Type u} (f : m (α → β)) (x : m α) : f >>= (. <$> x) = f <*> x
+  pure_bind      (x : α) (f : α → m β) : pure x >>= f = f x
+  bind_assoc     (x : m α) (f : α → m β) (g : β → m γ) : x >>= f >>= g = x >>= fun x => f x >>= g
+  map_pure g x    := (by rw [← bind_pure_comp, pure_bind])
+  seq_pure g x    := (by rw [← bind_map]; simp [map_pure, bind_pure_comp])
+  seq_assoc x g h := (by simp [← bind_pure_comp, ← bind_map, bind_assoc, pure_bind])
+
+export LawfulMonad (bind_pure_comp bind_map pure_bind bind_assoc)
+attribute [simp] pure_bind bind_assoc
+
+@[simp] theorem bind_pure [Monad m] [LawfulMonad m] (x : m α) : x >>= pure = x := by
+  show x >>= (fun a => pure (id a)) = x
+  rw [bind_pure_comp, id_map]
+
+theorem map_eq_pure_bind [Monad m] [LawfulMonad m] (f : α → β) (x : m α) : f <$> x = x >>= fun a => pure (f a) := by
+  rw [← bind_pure_comp]
+
+theorem seq_eq_bind_map {α β : Type u} [Monad m] [LawfulMonad m] (f : m (α → β)) (x : m α) : f <*> x = f >>= (. <$> x) := by
+  rw [← bind_map]
+
+theorem bind_congr [Bind m] {x : m α} {f g : α → m β} (h : ∀ a, f a = g a) : x >>= f = x >>= g := by
+  simp [funext h]
+
+@[simp] theorem bind_pure_unit [Monad m] [LawfulMonad m] {x : m PUnit} : (x >>= fun _ => pure ⟨⟩) = x := by
+  rw [bind_pure]
+
+theorem map_congr [Functor m] {x : m α} {f g : α → β} (h : ∀ a, f a = g a) : (f <$> x : m β) = g <$> x := by
+  simp [funext h]
+
+theorem seq_eq_bind {α β : Type u} [Monad m] [LawfulMonad m] (mf : m (α → β)) (x : m α) : mf <*> x = mf >>= fun f => f <$> x := by
+  rw [bind_map]
+
+theorem seqRight_eq_bind [Monad m] [LawfulMonad m] (x : m α) (y : m β) : x *> y = x >>= fun _ => y := by
+  rw [seqRight_eq]
+  simp [map_eq_pure_bind, seq_eq_bind_map, const]
+
+theorem seqLeft_eq_bind [Monad m] [LawfulMonad m] (x : m α) (y : m β) : x <* y = x >>= fun a => y >>= fun _ => pure a := by
+  rw [seqLeft_eq]; simp [map_eq_pure_bind, seq_eq_bind_map]
+
+/--
+An alternative constructor for `LawfulMonad` which has more
+defaultable fields in the common case.
+-/
+theorem LawfulMonad.mk' (m : Type u → Type v) [Monad m]
+    (id_map : ∀ {α} (x : m α), id <$> x = x)
+    (pure_bind : ∀ {α β} (x : α) (f : α → m β), pure x >>= f = f x)
+    (bind_assoc : ∀ {α β γ} (x : m α) (f : α → m β) (g : β → m γ),
+      x >>= f >>= g = x >>= fun x => f x >>= g)
+    (map_const : ∀ {α β} (x : α) (y : m β),
+      Functor.mapConst x y = Function.const β x <$> y := by intros; rfl)
+    (seqLeft_eq : ∀ {α β} (x : m α) (y : m β),
+      x <* y = (x >>= fun a => y >>= fun _ => pure a) := by intros; rfl)
+    (seqRight_eq : ∀ {α β} (x : m α) (y : m β), x *> y = (x >>= fun _ => y) := by intros; rfl)
+    (bind_pure_comp : ∀ {α β} (f : α → β) (x : m α),
+      x >>= (fun y => pure (f y)) = f <$> x := by intros; rfl)
+    (bind_map : ∀ {α β} (f : m (α → β)) (x : m α), f >>= (. <$> x) = f <*> x := by intros; rfl)
+    : LawfulMonad m :=
+  have map_pure {α β} (g : α → β) (x : α) : g <$> (pure x : m α) = pure (g x) := by
+    rw [← bind_pure_comp]; simp [pure_bind]
+  { id_map, bind_pure_comp, bind_map, pure_bind, bind_assoc, map_pure,
+    comp_map := by simp [← bind_pure_comp, bind_assoc, pure_bind]
+    pure_seq := by intros; rw [← bind_map]; simp [pure_bind]
+    seq_pure := by intros; rw [← bind_map]; simp [map_pure, bind_pure_comp]
+    seq_assoc := by simp [← bind_pure_comp, ← bind_map, bind_assoc, pure_bind]
+    map_const := funext fun x => funext (map_const x)
+    seqLeft_eq := by simp [seqLeft_eq, ← bind_map, ← bind_pure_comp, pure_bind, bind_assoc]
+    seqRight_eq := fun x y => by
+      rw [seqRight_eq, ← bind_map, ← bind_pure_comp, bind_assoc]; simp [pure_bind, id_map] }
+
+/-! # Id -/
+
+namespace Id
+
+@[simp] theorem map_eq (x : Id α) (f : α → β) : f <$> x = f x := rfl
+@[simp] theorem bind_eq (x : Id α) (f : α → id β) : x >>= f = f x := rfl
+@[simp] theorem pure_eq (a : α) : (pure a : Id α) = a := rfl
+
+instance : LawfulMonad Id := by
+  refine' { .. } <;> intros <;> rfl
+
+end Id
+
+/-! # Option -/
+
+instance : LawfulMonad Option := LawfulMonad.mk'
+  (id_map := fun x => by cases x <;> rfl)
+  (pure_bind := fun x f => rfl)
+  (bind_assoc := fun x f g => by cases x <;> rfl)
+  (bind_pure_comp := fun f x => by cases x <;> rfl)
+
+instance : LawfulApplicative Option := inferInstance
+instance : LawfulFunctor Option := inferInstance

src/Init/Control/Lawful/Instances.lean

@@ -0,0 +1,248 @@
+/-
+Copyright (c) 2021 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Sebastian Ullrich, Leonardo de Moura, Mario Carneiro
+-/
+prelude
+import Init.Control.Lawful.Basic
+import Init.Control.Except
+import Init.Control.StateRef
+
+open Function
+
+/-! # ExceptT -/
+
+namespace ExceptT
+
+theorem ext [Monad m] {x y : ExceptT ε m α} (h : x.run = y.run) : x = y := by
+  simp [run] at h
+  assumption
+
+@[simp] theorem run_pure [Monad m] (x : α) : run (pure x : ExceptT ε m α) = pure (Except.ok x) := rfl
+
+@[simp] theorem run_lift  [Monad.{u, v} m] (x : m α) : run (ExceptT.lift x : ExceptT ε m α) = (Except.ok <$> x : m (Except ε α)) := rfl
+
+@[simp] theorem run_throw [Monad m] : run (throw e : ExceptT ε m β) = pure (Except.error e) := rfl
+
+@[simp] theorem run_bind_lift [Monad m] [LawfulMonad m] (x : m α) (f : α → ExceptT ε m β) : run (ExceptT.lift x >>= f : ExceptT ε m β) = x >>= fun a => run (f a) := by
+  simp[ExceptT.run, ExceptT.lift, bind, ExceptT.bind, ExceptT.mk, ExceptT.bindCont, map_eq_pure_bind]
+
+@[simp] theorem bind_throw [Monad m] [LawfulMonad m] (f : α → ExceptT ε m β) : (throw e >>= f) = throw e := by
+  simp [throw, throwThe, MonadExceptOf.throw, bind, ExceptT.bind, ExceptT.bindCont, ExceptT.mk]
+
+theorem run_bind [Monad m] (x : ExceptT ε m α)
+        : run (x >>= f : ExceptT ε m β)
+          =
+          run x >>= fun
+                     | Except.ok x => run (f x)
+                     | Except.error e => pure (Except.error e) :=
+  rfl
+
+@[simp] theorem lift_pure [Monad m] [LawfulMonad m] (a : α) : ExceptT.lift (pure a) = (pure a : ExceptT ε m α) := by
+  simp [ExceptT.lift, pure, ExceptT.pure]
+
+@[simp] theorem run_map [Monad m] [LawfulMonad m] (f : α → β) (x : ExceptT ε m α)
+    : (f <$> x).run = Except.map f <$> x.run := by
+  simp [Functor.map, ExceptT.map, map_eq_pure_bind]
+  apply bind_congr
+  intro a; cases a <;> simp [Except.map]
+
+protected theorem seq_eq {α β ε : Type u} [Monad m] (mf : ExceptT ε m (α → β)) (x : ExceptT ε m α) : mf <*> x = mf >>= fun f => f <$> x :=
+  rfl
+
+protected theorem bind_pure_comp [Monad m] [LawfulMonad m] (f : α → β) (x : ExceptT ε m α) : x >>= pure ∘ f = f <$> x := by
+  intros; rfl
+
+protected theorem seqLeft_eq {α β ε : Type u} {m : Type u → Type v} [Monad m] [LawfulMonad m] (x : ExceptT ε m α) (y : ExceptT ε m β) : x <* y = const β <$> x <*> y := by
+  show (x >>= fun a => y >>= fun _ => pure a) = (const (α := α) β <$> x) >>= fun f => f <$> y
+  rw [← ExceptT.bind_pure_comp]
+  apply ext
+  simp [run_bind]
+  apply bind_congr
+  intro
+  | Except.error _ => simp
+  | Except.ok _ =>
+    simp [map_eq_pure_bind]; apply bind_congr; intro b;
+    cases b <;> simp [comp, Except.map, const]
+
+protected theorem seqRight_eq [Monad m] [LawfulMonad m] (x : ExceptT ε m α) (y : ExceptT ε m β) : x *> y = const α id <$> x <*> y := by
+  show (x >>= fun _ => y) = (const α id <$> x) >>= fun f => f <$> y
+  rw [← ExceptT.bind_pure_comp]
+  apply ext
+  simp [run_bind]
+  apply bind_congr
+  intro a; cases a <;> simp
+
+instance [Monad m] [LawfulMonad m] : LawfulMonad (ExceptT ε m) where
+  id_map         := by intros; apply ext; simp
+  map_const      := by intros; rfl
+  seqLeft_eq     := ExceptT.seqLeft_eq
+  seqRight_eq    := ExceptT.seqRight_eq
+  pure_seq       := by intros; apply ext; simp [ExceptT.seq_eq, run_bind]
+  bind_pure_comp := ExceptT.bind_pure_comp
+  bind_map       := by intros; rfl
+  pure_bind      := by intros; apply ext; simp [run_bind]
+  bind_assoc     := by intros; apply ext; simp [run_bind]; apply bind_congr; intro a; cases a <;> simp
+
+end ExceptT
+
+/-! # Except -/
+
+instance : LawfulMonad (Except ε) := LawfulMonad.mk'
+  (id_map := fun x => by cases x <;> rfl)
+  (pure_bind := fun a f => rfl)
+  (bind_assoc := fun a f g => by cases a <;> rfl)
+
+instance : LawfulApplicative (Except ε) := inferInstance
+instance : LawfulFunctor (Except ε) := inferInstance
+
+/-! # ReaderT -/
+
+namespace ReaderT
+
+theorem ext {x y : ReaderT ρ m α} (h : ∀ ctx, x.run ctx = y.run ctx) : x = y := by
+  simp [run] at h
+  exact funext h
+
+@[simp] theorem run_pure [Monad m] (a : α) (ctx : ρ) : (pure a : ReaderT ρ m α).run ctx = pure a := rfl
+
+@[simp] theorem run_bind [Monad m] (x : ReaderT ρ m α) (f : α → ReaderT ρ m β) (ctx : ρ)
+    : (x >>= f).run ctx = x.run ctx >>= λ a => (f a).run ctx := rfl
+
+@[simp] theorem run_mapConst [Monad m] (a : α) (x : ReaderT ρ m β) (ctx : ρ)
+    : (Functor.mapConst a x).run ctx = Functor.mapConst a (x.run ctx) := rfl
+
+@[simp] theorem run_map [Monad m] (f : α → β) (x : ReaderT ρ m α) (ctx : ρ)
+    : (f <$> x).run ctx = f <$> x.run ctx := rfl
+
+@[simp] theorem run_monadLift [MonadLiftT n m] (x : n α) (ctx : ρ)
+    : (monadLift x : ReaderT ρ m α).run ctx = (monadLift x : m α) := rfl
+
+@[simp] theorem run_monadMap [MonadFunctor n m] (f : {β : Type u} → n β → n β) (x : ReaderT ρ m α) (ctx : ρ)
+    : (monadMap @f x : ReaderT ρ m α).run ctx = monadMap @f (x.run ctx) := rfl
+
+@[simp] theorem run_read [Monad m] (ctx : ρ) : (ReaderT.read : ReaderT ρ m ρ).run ctx = pure ctx := rfl
+
+@[simp] theorem run_seq {α β : Type u} [Monad m] (f : ReaderT ρ m (α → β)) (x : ReaderT ρ m α) (ctx : ρ)
+    : (f <*> x).run ctx = (f.run ctx <*> x.run ctx) := rfl
+
+@[simp] theorem run_seqRight [Monad m] (x : ReaderT ρ m α) (y : ReaderT ρ m β) (ctx : ρ)
+    : (x *> y).run ctx = (x.run ctx *> y.run ctx) := rfl
+
+@[simp] theorem run_seqLeft [Monad m] (x : ReaderT ρ m α) (y : ReaderT ρ m β) (ctx : ρ)
+    : (x <* y).run ctx = (x.run ctx <* y.run ctx) := rfl
+
+instance [Monad m] [LawfulFunctor m] : LawfulFunctor (ReaderT ρ m) where
+  id_map    := by intros; apply ext; simp
+  map_const := by intros; funext a b; apply ext; intros; simp [map_const]
+  comp_map  := by intros; apply ext; intros; simp [comp_map]
+
+instance [Monad m] [LawfulApplicative m] : LawfulApplicative (ReaderT ρ m) where
+  seqLeft_eq  := by intros; apply ext; intros; simp [seqLeft_eq]
+  seqRight_eq := by intros; apply ext; intros; simp [seqRight_eq]
+  pure_seq    := by intros; apply ext; intros; simp [pure_seq]
+  map_pure    := by intros; apply ext; intros; simp [map_pure]
+  seq_pure    := by intros; apply ext; intros; simp [seq_pure]
+  seq_assoc   := by intros; apply ext; intros; simp [seq_assoc]
+
+instance [Monad m] [LawfulMonad m] : LawfulMonad (ReaderT ρ m) where
+  bind_pure_comp := by intros; apply ext; intros; simp [LawfulMonad.bind_pure_comp]
+  bind_map       := by intros; apply ext; intros; simp [bind_map]
+  pure_bind      := by intros; apply ext; intros; simp
+  bind_assoc     := by intros; apply ext; intros; simp
+
+end ReaderT
+
+/-! # StateRefT -/
+
+instance [Monad m] [LawfulMonad m] : LawfulMonad (StateRefT' ω σ m) :=
+  inferInstanceAs (LawfulMonad (ReaderT (ST.Ref ω σ) m))
+
+/-! # StateT -/
+
+namespace StateT
+
+theorem ext {x y : StateT σ m α} (h : ∀ s, x.run s = y.run s) : x = y :=
+  funext h
+
+@[simp] theorem run'_eq [Monad m] (x : StateT σ m α) (s : σ) : run' x s = (·.1) <$> run x s :=
+  rfl
+
+@[simp] theorem run_pure [Monad m] (a : α) (s : σ) : (pure a : StateT σ m α).run s = pure (a, s) := rfl
+
+@[simp] theorem run_bind [Monad m] (x : StateT σ m α) (f : α → StateT σ m β) (s : σ)
+    : (x >>= f).run s = x.run s >>= λ p => (f p.1).run p.2 := by
+  simp [bind, StateT.bind, run]
+
+@[simp] theorem run_map {α β σ : Type u} [Monad m] [LawfulMonad m] (f : α → β) (x : StateT σ m α) (s : σ) : (f <$> x).run s = (fun (p : α × σ) => (f p.1, p.2)) <$> x.run s := by
+  simp [Functor.map, StateT.map, run, map_eq_pure_bind]
+
+@[simp] theorem run_get [Monad m] (s : σ)    : (get : StateT σ m σ).run s = pure (s, s) := rfl
+
+@[simp] theorem run_set [Monad m] (s s' : σ) : (set s' : StateT σ m PUnit).run s = pure (⟨⟩, s') := rfl
+
+@[simp] theorem run_modify [Monad m] (f : σ → σ) (s : σ) : (modify f : StateT σ m PUnit).run s = pure (⟨⟩, f s) := rfl
+
+@[simp] theorem run_modifyGet [Monad m] (f : σ → α × σ) (s : σ) : (modifyGet f : StateT σ m α).run s = pure ((f s).1, (f s).2) := by
+  simp [modifyGet, MonadStateOf.modifyGet, StateT.modifyGet, run]
+
+@[simp] theorem run_lift {α σ : Type u} [Monad m] (x : m α) (s : σ) : (StateT.lift x : StateT σ m α).run s = x >>= fun a => pure (a, s) := rfl
+
+@[simp] theorem run_bind_lift {α σ : Type u} [Monad m] [LawfulMonad m] (x : m α) (f : α → StateT σ m β) (s : σ) : (StateT.lift x >>= f).run s = x >>= fun a => (f a).run s := by
+  simp [StateT.lift, StateT.run, bind, StateT.bind]
+
+@[simp] theorem run_monadLift {α σ : Type u} [Monad m] [MonadLiftT n m] (x : n α) (s : σ) : (monadLift x : StateT σ m α).run s = (monadLift x : m α) >>= fun a => pure (a, s) := rfl
+
+@[simp] theorem run_monadMap [Monad m] [MonadFunctor n m] (f : {β : Type u} → n β → n β) (x : StateT σ m α) (s : σ)
+    : (monadMap @f x : StateT σ m α).run s = monadMap @f (x.run s) := rfl
+
+@[simp] theorem run_seq {α β σ : Type u} [Monad m] [LawfulMonad m] (f : StateT σ m (α → β)) (x : StateT σ m α) (s : σ) : (f <*> x).run s = (f.run s >>= fun fs => (fun (p : α × σ) => (fs.1 p.1, p.2)) <$> x.run fs.2) := by
+  show (f >>= fun g => g <$> x).run s = _
+  simp
+
+@[simp] theorem run_seqRight [Monad m] [LawfulMonad m] (x : StateT σ m α) (y : StateT σ m β) (s : σ) : (x *> y).run s = (x.run s >>= fun p => y.run p.2) := by
+  show (x >>= fun _ => y).run s = _
+  simp
+
+@[simp] theorem run_seqLeft {α β σ : Type u} [Monad m] [LawfulMonad m] (x : StateT σ m α) (y : StateT σ m β) (s : σ) : (x <* y).run s = (x.run s >>= fun p => y.run p.2 >>= fun p' => pure (p.1, p'.2)) := by
+  show (x >>= fun a => y >>= fun _ => pure a).run s = _
+  simp
+
+theorem seqRight_eq [Monad m] [LawfulMonad m] (x : StateT σ m α) (y : StateT σ m β) : x *> y = const α id <$> x <*> y := by
+  apply ext; intro s
+  simp [map_eq_pure_bind, const]
+  apply bind_congr; intro p; cases p
+  simp [Prod.eta]
+
+theorem seqLeft_eq [Monad m] [LawfulMonad m] (x : StateT σ m α) (y : StateT σ m β) : x <* y = const β <$> x <*> y := by
+  apply ext; intro s
+  simp [map_eq_pure_bind]
+
+instance [Monad m] [LawfulMonad m] : LawfulMonad (StateT σ m) where
+  id_map         := by intros; apply ext; intros; simp[Prod.eta]
+  map_const      := by intros; rfl
+  seqLeft_eq     := seqLeft_eq
+  seqRight_eq    := seqRight_eq
+  pure_seq       := by intros; apply ext; intros; simp
+  bind_pure_comp := by intros; apply ext; intros; simp; apply LawfulMonad.bind_pure_comp
+  bind_map       := by intros; rfl
+  pure_bind      := by intros; apply ext; intros; simp
+  bind_assoc     := by intros; apply ext; intros; simp
+
+end StateT
+
+/-! # EStateM -/
+
+instance : LawfulMonad (EStateM ε σ) := .mk'
+  (id_map := fun x => funext <| fun s => by
+    dsimp only [EStateM.instMonad, EStateM.map]
+    match x s with
+    | .ok _ _ => rfl
+    | .error _ _ => rfl)
+  (pure_bind := fun _ _ => rfl)
+  (bind_assoc := fun x _ _ => funext <| fun s => by
+    dsimp only [EStateM.instMonad, EStateM.bind]
+    match x s with
+    | .ok _ _ => rfl
+    | .error _ _ => rfl)
+  (map_const := fun _ _ => rfl)

src/Init/Control/StateCps.lean

@@ -4,7 +4,7 @@ Released under Apache 2.0 license as described in the file LICENSE.
 Authors: Leonardo de Moura
 -/
 prelude
-import Init.Control.Lawful
+import Init.Control.Lawful.Basic
 
 /-!
 The State monad transformer using CPS style.

src/Init/Conv.lean

@@ -6,7 +6,7 @@ Authors: Leonardo de Moura
 Notation for operators defined at Prelude.lean
 -/
 prelude
-import Init.NotationExtra
+import Init.Tactics
 
 namespace Lean.Parser.Tactic.Conv
 
@@ -54,6 +54,10 @@ syntax (name := lhs) "lhs" : conv
 (In general, for an `n`-ary operator, it traverses into the last argument.) -/
 syntax (name := rhs) "rhs" : conv
 
+/-- Traverses into the function of a (unary) function application.
+For example, `| f a b` turns into `| f a`. (Use `arg 0` to traverse into `f`.)  -/
+syntax (name := «fun») "fun" : conv
+
 /-- Reduces the target to Weak Head Normal Form. This reduces definitions
 in "head position" until a constructor is exposed. For example, `List.map f [a, b, c]`
 weak head normalizes to `f a :: List.map f [b, c]`. -/
@@ -74,7 +78,8 @@ syntax (name := congr) "congr" : conv
 * `arg i` traverses into the `i`'th argument of the target. For example if the
   target is `f a b c d` then `arg 1` traverses to `a` and `arg 3` traverses to `c`.
 * `arg @i` is the same as `arg i` but it counts all arguments instead of just the
-  explicit arguments. -/
+  explicit arguments.
+* `arg 0` traverses into the function. If the target is `f a b c d`, `arg 0` traverses into `f`. -/
 syntax (name := arg) "arg " "@"? num : conv
 
 /-- `ext x` traverses into a binder (a `fun x => e` or `∀ x, e` expression)
@@ -151,7 +156,6 @@ match [a, b] with
 simplifies to `a`. -/
 syntax (name := simpMatch) "simp_match" : conv
 
-
 /-- Executes the given tactic block without converting `conv` goal into a regular goal. -/
 syntax (name := nestedTacticCore) "tactic'" " => " tacticSeq : conv
 
@@ -197,7 +201,7 @@ macro (name := anyGoals) tk:"any_goals " s:convSeq : conv =>
   with inaccessible names to the given names.
 * `case tag₁ | tag₂ => tac` is equivalent to `(case tag₁ => tac); (case tag₂ => tac)`.
 -/
-macro (name := case) tk:"case " args:sepBy1(caseArg, " | ") arr:" => " s:convSeq : conv =>
+macro (name := case) tk:"case " args:sepBy1(caseArg, "|") arr:" => " s:convSeq : conv =>
   `(conv| tactic' => case%$tk $args|* =>%$arr conv' => ($s); all_goals rfl)
 
 /--
@@ -206,7 +210,7 @@ has been solved after applying `tac`, nor admits the goal if `tac` failed.
 Recall that `case` closes the goal using `sorry` when `tac` fails, and
 the tactic execution is not interrupted.
 -/
-macro (name := case') tk:"case' " args:sepBy1(caseArg, " | ") arr:" => " s:convSeq : conv =>
+macro (name := case') tk:"case' " args:sepBy1(caseArg, "|") arr:" => " s:convSeq : conv =>
   `(conv| tactic' => case'%$tk $args|* =>%$arr conv' => $s)
 
 /--
@@ -303,4 +307,7 @@ Basic forms:
 -- refer to the syntax category instead of this syntax
 syntax (name := conv) "conv" (" at " ident)? (" in " (occs)? term)? " => " convSeq : tactic
 
+/-- `norm_cast` tactic in `conv` mode. -/
+syntax (name := normCast) "norm_cast" : conv
+
 end Lean.Parser.Tactic.Conv

src/Init/Core.lean

@@ -17,7 +17,9 @@ universe u v w
 at the application site itself (by comparison to the `@[inline]` attribute,
 which applies to all applications of the function).
 -/
-def inline {α : Sort u} (a : α) : α := a
+@[simp] def inline {α : Sort u} (a : α) : α := a
+
+theorem id_def {α : Sort u} (a : α) : id a = a := rfl
 
 /--
 `flip f a b` is `f b a`. It is useful for "point-free" programming,
@@ -32,8 +34,32 @@ and `flip (·<·)` is the greater-than relation.
 
 @[simp] theorem Function.comp_apply {f : β → δ} {g : α → β} {x : α} : comp f g x = f (g x) := rfl
 
+theorem Function.comp_def {α β δ} (f : β → δ) (g : α → β) : f ∘ g = fun x => f (g x) := rfl
+
 attribute [simp] namedPattern
 
+/--
+`Empty.elim : Empty → C` says that a value of any type can be constructed from
+`Empty`. This can be thought of as a compiler-checked assertion that a code path is unreachable.
+
+This is a non-dependent variant of `Empty.rec`.
+-/
+@[macro_inline] def Empty.elim {C : Sort u} : Empty → C := Empty.rec
+
+/-- Decidable equality for Empty -/
+instance : DecidableEq Empty := fun a => a.elim
+
+/--
+`PEmpty.elim : Empty → C` says that a value of any type can be constructed from
+`PEmpty`. This can be thought of as a compiler-checked assertion that a code path is unreachable.
+
+This is a non-dependent variant of `PEmpty.rec`.
+-/
+@[macro_inline] def PEmpty.elim {C : Sort _} : PEmpty → C := fun a => nomatch a
+
+/-- Decidable equality for PEmpty -/
+instance : DecidableEq PEmpty := fun a => a.elim
+
 /--
   Thunks are "lazy" values that are evaluated when first accessed using `Thunk.get/map/bind`.
   The value is then stored and not recomputed for all further accesses. -/
@@ -78,6 +104,8 @@ instance thunkCoe : CoeTail α (Thunk α) where
 abbrev Eq.ndrecOn.{u1, u2} {α : Sort u2} {a : α} {motive : α → Sort u1} {b : α} (h : a = b) (m : motive a) : motive b :=
   Eq.ndrec m h
 
+/-! # definitions  -/
+
 /--
 If and only if, or logical bi-implication. `a ↔ b` means that `a` implies `b` and vice versa.
 By `propext`, this implies that `a` and `b` are equal and hence any expression involving `a`
@@ -126,6 +154,10 @@ inductive PSum (α : Sort u) (β : Sort v) where
 
 @[inherit_doc] infixr:30 " ⊕' " => PSum
 
+instance {α β} [Inhabited α] : Inhabited (PSum α β) := ⟨PSum.inl default⟩
+
+instance {α β} [Inhabited β] : Inhabited (PSum α β) := ⟨PSum.inr default⟩
+
 /--
 `Sigma β`, also denoted `Σ a : α, β a` or `(a : α) × β a`, is the type of dependent pairs
 whose first component is `a : α` and whose second component is `b : β a`
@@ -133,6 +165,7 @@ whose first component is `a : α` and whose second component is `b : β a`
 It is sometimes known as the dependent sum type, since it is the type level version
 of an indexed summation.
 -/
+@[pp_using_anonymous_constructor]
 structure Sigma {α : Type u} (β : α → Type v) where
   /-- Constructor for a dependent pair. If `a : α` and `b : β a` then `⟨a, b⟩ : Sigma β`.
   (This will usually require a type ascription to determine `β`
@@ -158,6 +191,7 @@ which can cause problems for universe level unification,
 because the equation `max 1 u v = ?u + 1` has no solution in level arithmetic.
 `PSigma` is usually only used in automation that constructs pairs of arbitrary types.
 -/
+@[pp_using_anonymous_constructor]
 structure PSigma {α : Sort u} (β : α → Sort v) where
   /-- Constructor for a dependent pair. If `a : α` and `b : β a` then `⟨a, b⟩ : PSigma β`.
   (This will usually require a type ascription to determine `β`
@@ -342,6 +376,70 @@ class HasEquiv (α : Sort u) where
 
 @[inherit_doc] infix:50 " ≈ "  => HasEquiv.Equiv
 
+/-! # set notation  -/
+
+/-- Notation type class for the subset relation `⊆`. -/
+class HasSubset (α : Type u) where
+  /-- Subset relation: `a ⊆ b`  -/
+  Subset : α → α → Prop
+export HasSubset (Subset)
+
+/-- Notation type class for the strict subset relation `⊂`. -/
+class HasSSubset (α : Type u) where
+  /-- Strict subset relation: `a ⊂ b`  -/
+  SSubset : α → α → Prop
+export HasSSubset (SSubset)
+
+/-- Superset relation: `a ⊇ b`  -/
+abbrev Superset [HasSubset α] (a b : α) := Subset b a
+
+/-- Strict superset relation: `a ⊃ b`  -/
+abbrev SSuperset [HasSSubset α] (a b : α) := SSubset b a
+
+/-- Notation type class for the union operation `∪`. -/
+class Union (α : Type u) where
+  /-- `a ∪ b` is the union of`a` and `b`. -/
+  union : α → α → α
+
+/-- Notation type class for the intersection operation `∩`. -/
+class Inter (α : Type u) where
+  /-- `a ∩ b` is the intersection of`a` and `b`. -/
+  inter : α → α → α
+
+/-- Notation type class for the set difference `\`. -/
+class SDiff (α : Type u) where
+  /--
+  `a \ b` is the set difference of `a` and `b`,
+  consisting of all elements in `a` that are not in `b`.
+  -/
+  sdiff : α → α → α
+
+/-- Subset relation: `a ⊆ b`  -/
+infix:50 " ⊆ " => Subset
+
+/-- Strict subset relation: `a ⊂ b`  -/
+infix:50 " ⊂ " => SSubset
+
+/-- Superset relation: `a ⊇ b`  -/
+infix:50 " ⊇ " => Superset
+
+/-- Strict superset relation: `a ⊃ b`  -/
+infix:50 " ⊃ " => SSuperset
+
+/-- `a ∪ b` is the union of`a` and `b`. -/
+infixl:65 " ∪ " => Union.union
+
+/-- `a ∩ b` is the intersection of`a` and `b`. -/
+infixl:70 " ∩ " => Inter.inter
+
+/--
+`a \ b` is the set difference of `a` and `b`,
+consisting of all elements in `a` that are not in `b`.
+-/
+infix:70 " \\ " => SDiff.sdiff
+
+/-! # collections  -/
+
 /-- `EmptyCollection α` is the typeclass which supports the notation `∅`, also written as `{}`. -/
 class EmptyCollection (α : Type u) where
   /-- `∅` or `{}` is the empty set or empty collection.
@@ -351,6 +449,36 @@ class EmptyCollection (α : Type u) where
 @[inherit_doc] notation "{" "}" => EmptyCollection.emptyCollection
 @[inherit_doc] notation "∅"     => EmptyCollection.emptyCollection
 
+/--
+Type class for the `insert` operation.
+Used to implement the `{ a, b, c }` syntax.
+-/
+class Insert (α : outParam <| Type u) (γ : Type v) where
+  /-- `insert x xs` inserts the element `x` into the collection `xs`. -/
+  insert : α → γ → γ
+export Insert (insert)
+
+/--
+Type class for the `singleton` operation.
+Used to implement the `{ a, b, c }` syntax.
+-/
+class Singleton (α : outParam <| Type u) (β : Type v) where
+  /-- `singleton x` is a collection with the single element `x` (notation: `{x}`). -/
+  singleton : α → β
+export Singleton (singleton)
+
+/-- `insert x ∅ = {x}` -/
+class IsLawfulSingleton (α : Type u) (β : Type v) [EmptyCollection β] [Insert α β] [Singleton α β] :
+    Prop where
+  /-- `insert x ∅ = {x}` -/
+  insert_emptyc_eq (x : α) : (insert x ∅ : β) = singleton x
+export IsLawfulSingleton (insert_emptyc_eq)
+
+/-- Type class used to implement the notation `{ a ∈ c | p a }` -/
+class Sep (α : outParam <| Type u) (γ : Type v) where
+  /-- Computes `{ a ∈ c | p a }`. -/
+  sep : (α → Prop) → γ → γ
+
 /--
 `Task α` is a primitive for asynchronous computation.
 It represents a computation that will resolve to a value of type `α`,
@@ -525,9 +653,7 @@ theorem not_not_intro {p : Prop} (h : p) : ¬ ¬ p :=
   fun hn : ¬ p => hn h
 
 -- proof irrelevance is built in
-theorem proofIrrel {a : Prop} (h₁ h₂ : a) : h₁ = h₂ := rfl
-
-theorem id.def {α : Sort u} (a : α) : id a = a := rfl
+theorem proof_irrel {a : Prop} (h₁ h₂ : a) : h₁ = h₂ := rfl
 
 /--
 If `h : α = β` is a proof of type equality, then `h.mp : α → β` is the induced
@@ -553,7 +679,7 @@ You can prove theorems about the resulting element by induction on `h`, since
 theorem Eq.substr {α : Sort u} {p : α → Prop} {a b : α} (h₁ : b = a) (h₂ : p a) : p b :=
   h₁ ▸ h₂
 
-theorem cast_eq {α : Sort u} (h : α = α) (a : α) : cast h a = a :=
+@[simp] theorem cast_eq {α : Sort u} (h : α = α) (a : α) : cast h a = a :=
   rfl
 
 /--
@@ -575,8 +701,9 @@ theorem Ne.elim (h : a ≠ b) : a = b → False := h
 
 theorem Ne.irrefl (h : a ≠ a) : False := h rfl
 
-theorem Ne.symm (h : a ≠ b) : b ≠ a :=
-  fun h₁ => h (h₁.symm)
+theorem Ne.symm (h : a ≠ b) : b ≠ a := fun h₁ => h (h₁.symm)
+
+theorem ne_comm {α} {a b : α} : a ≠ b ↔ b ≠ a := ⟨Ne.symm, Ne.symm⟩
 
 theorem false_of_ne : a ≠ a → False := Ne.irrefl
 
@@ -588,8 +715,8 @@ theorem ne_true_of_not : ¬p → p ≠ True :=
     have : ¬True := h ▸ hnp
     this trivial
 
-theorem true_ne_false : ¬True = False :=
-  ne_false_of_self trivial
+theorem true_ne_false : ¬True = False := ne_false_of_self trivial
+theorem false_ne_true : False ≠ True := fun h => h.symm ▸ trivial
 
 end Ne
 
@@ -612,13 +739,16 @@ theorem beq_false_of_ne [BEq α] [LawfulBEq α] {a b : α} (h : a ≠ b) : (a ==
 section
 variable {α β φ : Sort u} {a a' : α} {b b' : β} {c : φ}
 
-theorem HEq.ndrec.{u1, u2} {α : Sort u2} {a : α} {motive : {β : Sort u2} → β → Sort u1} (m : motive a) {β : Sort u2} {b : β} (h : HEq a b) : motive b :=
+/-- Non-dependent recursor for `HEq` -/
+noncomputable def HEq.ndrec.{u1, u2} {α : Sort u2} {a : α} {motive : {β : Sort u2} → β → Sort u1} (m : motive a) {β : Sort u2} {b : β} (h : HEq a b) : motive b :=
   h.rec m
 
-theorem HEq.ndrecOn.{u1, u2} {α : Sort u2} {a : α} {motive : {β : Sort u2} → β → Sort u1} {β : Sort u2} {b : β} (h : HEq a b) (m : motive a) : motive b :=
+/-- `HEq.ndrec` variant -/
+noncomputable def HEq.ndrecOn.{u1, u2} {α : Sort u2} {a : α} {motive : {β : Sort u2} → β → Sort u1} {β : Sort u2} {b : β} (h : HEq a b) (m : motive a) : motive b :=
   h.rec m
 
-theorem HEq.elim {α : Sort u} {a : α} {p : α → Sort v} {b : α} (h₁ : HEq a b) (h₂ : p a) : p b :=
+/-- `HEq.ndrec` variant -/
+noncomputable def HEq.elim {α : Sort u} {a : α} {p : α → Sort v} {b : α} (h₁ : HEq a b) (h₂ : p a) : p b :=
   eq_of_heq h₁ ▸ h₂
 
 theorem HEq.subst {p : (T : Sort u) → T → Prop} (h₁ : HEq a b) (h₂ : p α a) : p β b :=
@@ -668,22 +798,29 @@ protected theorem Iff.rfl {a : Prop} : a ↔ a :=
 
 macro_rules | `(tactic| rfl) => `(tactic| exact Iff.rfl)
 
+theorem Iff.of_eq (h : a = b) : a ↔ b := h ▸ Iff.rfl
+
 theorem Iff.trans (h₁ : a ↔ b) (h₂ : b ↔ c) : a ↔ c :=
-  Iff.intro
-    (fun ha => Iff.mp h₂ (Iff.mp h₁ ha))
-    (fun hc => Iff.mpr h₁ (Iff.mpr h₂ hc))
+  Iff.intro (h₂.mp ∘ h₁.mp) (h₁.mpr ∘ h₂.mpr)
 
-theorem Iff.symm (h : a ↔ b) : b ↔ a :=
-  Iff.intro (Iff.mpr h) (Iff.mp h)
+-- This is needed for `calc` to work with `iff`.
+instance : Trans Iff Iff Iff where
+  trans := Iff.trans
 
-theorem Iff.comm : (a ↔ b) ↔ (b ↔ a) :=
-  Iff.intro Iff.symm Iff.symm
+theorem Eq.comm {a b : α} : a = b ↔ b = a := Iff.intro Eq.symm Eq.symm
+theorem eq_comm {a b : α} : a = b ↔ b = a := Eq.comm
 
-theorem Iff.of_eq (h : a = b) : a ↔ b :=
-  h ▸ Iff.refl _
+theorem Iff.symm (h : a ↔ b) : b ↔ a := Iff.intro h.mpr h.mp
+theorem Iff.comm: (a ↔ b) ↔ (b ↔ a) := Iff.intro Iff.symm Iff.symm
+theorem iff_comm : (a ↔ b) ↔ (b ↔ a) := Iff.comm
 
-theorem And.comm : a ∧ b ↔ b ∧ a := by
-  constructor <;> intro ⟨h₁, h₂⟩ <;> exact ⟨h₂, h₁⟩
+theorem And.symm : a ∧ b → b ∧ a := fun ⟨ha, hb⟩ => ⟨hb, ha⟩
+theorem And.comm : a ∧ b ↔ b ∧ a := Iff.intro And.symm And.symm
+theorem and_comm : a ∧ b ↔ b ∧ a := And.comm
+
+theorem Or.symm : a ∨ b → b ∨ a := .rec .inr .inl
+theorem Or.comm : a ∨ b ↔ b ∨ a := Iff.intro Or.symm Or.symm
+theorem or_comm : a ∨ b ↔ b ∨ a := Or.comm
 
 /-! # Exists -/
 
@@ -883,8 +1020,13 @@ protected theorem Subsingleton.helim {α β : Sort u} [h₁ : Subsingleton α] (
   apply heq_of_eq
   apply Subsingleton.elim
 
-instance (p : Prop) : Subsingleton p :=
-  ⟨fun a b => proofIrrel a b⟩
+instance (p : Prop) : Subsingleton p := ⟨fun a b => proof_irrel a b⟩
+
+instance : Subsingleton Empty  := ⟨(·.elim)⟩
+instance : Subsingleton PEmpty := ⟨(·.elim)⟩
+
+instance [Subsingleton α] [Subsingleton β] : Subsingleton (α × β) :=
+  ⟨fun {..} {..} => by congr <;> apply Subsingleton.elim⟩
 
 instance (p : Prop) : Subsingleton (Decidable p) :=
   Subsingleton.intro fun
@@ -895,6 +1037,9 @@ instance (p : Prop) : Subsingleton (Decidable p) :=
       | isTrue t₂  => absurd t₂ f₁
       | isFalse _  => rfl
 
+example [Subsingleton α] (p : α → Prop) : Subsingleton (Subtype p) :=
+  ⟨fun ⟨x, _⟩ ⟨y, _⟩ => by congr; exact Subsingleton.elim x y⟩
+
 theorem recSubsingleton
      {p : Prop} [h : Decidable p]
      {h₁ : p → Sort u}
@@ -1163,7 +1308,6 @@ gen_injective_theorems% Fin
 gen_injective_theorems% Array
 gen_injective_theorems% Sum
 gen_injective_theorems% PSum
-gen_injective_theorems% Nat
 gen_injective_theorems% Option
 gen_injective_theorems% List
 gen_injective_theorems% Except
@@ -1171,15 +1315,126 @@ gen_injective_theorems% EStateM.Result
 gen_injective_theorems% Lean.Name
 gen_injective_theorems% Lean.Syntax
 
+theorem Nat.succ.inj {m n : Nat} : m.succ = n.succ → m = n :=
+  fun x => Nat.noConfusion x id
+
+theorem Nat.succ.injEq (u v : Nat) : (u.succ = v.succ) = (u = v) :=
+  Eq.propIntro Nat.succ.inj (congrArg Nat.succ)
+
 @[simp] theorem beq_iff_eq [BEq α] [LawfulBEq α] (a b : α) : a == b ↔ a = b :=
   ⟨eq_of_beq, by intro h; subst h; exact LawfulBEq.rfl⟩
 
-/-! # Quotients -/
+/-! # Prop lemmas -/
+
+/-- *Ex falso* for negation: from `¬a` and `a` anything follows. This is the same as `absurd` with
+the arguments flipped, but it is in the `Not` namespace so that projection notation can be used. -/
+def Not.elim {α : Sort _} (H1 : ¬a) (H2 : a) : α := absurd H2 H1
+
+/-- Non-dependent eliminator for `And`. -/
+abbrev And.elim (f : a → b → α) (h : a ∧ b) : α := f h.left h.right
+
+/-- Non-dependent eliminator for `Iff`. -/
+def Iff.elim (f : (a → b) → (b → a) → α) (h : a ↔ b) : α := f h.mp h.mpr
 
 /-- Iff can now be used to do substitutions in a calculation -/
 theorem Iff.subst {a b : Prop} {p : Prop → Prop} (h₁ : a ↔ b) (h₂ : p a) : p b :=
   Eq.subst (propext h₁) h₂
 
+theorem Not.intro {a : Prop} (h : a → False) : ¬a := h
+
+theorem Not.imp {a b : Prop} (H2 : ¬b) (H1 : a → b) : ¬a := mt H1 H2
+
+theorem not_congr (h : a ↔ b) : ¬a ↔ ¬b := ⟨mt h.2, mt h.1⟩
+
+theorem not_not_not : ¬¬¬a ↔ ¬a := ⟨mt not_not_intro, not_not_intro⟩
+
+theorem iff_of_true (ha : a) (hb : b) : a ↔ b := Iff.intro (fun _ => hb) (fun _ => ha)
+theorem iff_of_false (ha : ¬a) (hb : ¬b) : a ↔ b := Iff.intro ha.elim hb.elim
+
+theorem iff_true_left  (ha : a) : (a ↔ b) ↔ b := Iff.intro (·.mp ha) (iff_of_true ha)
+theorem iff_true_right (ha : a) : (b ↔ a) ↔ b := Iff.comm.trans (iff_true_left ha)
+
+theorem iff_false_left  (ha : ¬a) : (a ↔ b) ↔ ¬b := Iff.intro (mt ·.mpr ha) (iff_of_false ha)
+theorem iff_false_right (ha : ¬a) : (b ↔ a) ↔ ¬b := Iff.comm.trans (iff_false_left ha)
+
+theorem of_iff_true    (h : a ↔ True) : a := h.mpr trivial
+theorem iff_true_intro (h : a) : a ↔ True := iff_of_true h trivial
+
+theorem not_of_iff_false : (p ↔ False) → ¬p := Iff.mp
+theorem iff_false_intro (h : ¬a) : a ↔ False := iff_of_false h id
+
+theorem not_iff_false_intro (h : a) : ¬a ↔ False := iff_false_intro (not_not_intro h)
+theorem not_true : (¬True) ↔ False := iff_false_intro (not_not_intro trivial)
+
+theorem not_false_iff : (¬False) ↔ True := iff_true_intro not_false
+
+theorem Eq.to_iff : a = b → (a ↔ b) := Iff.of_eq
+theorem iff_of_eq : a = b → (a ↔ b) := Iff.of_eq
+theorem neq_of_not_iff : ¬(a ↔ b) → a ≠ b := mt Iff.of_eq
+
+theorem iff_iff_eq : (a ↔ b) ↔ a = b := Iff.intro propext Iff.of_eq
+@[simp] theorem eq_iff_iff : (a = b) ↔ (a ↔ b) := iff_iff_eq.symm
+
+theorem eq_self_iff_true (a : α)  : a = a ↔ True  := iff_true_intro rfl
+theorem ne_self_iff_false (a : α) : a ≠ a ↔ False := not_iff_false_intro rfl
+
+theorem false_of_true_iff_false (h : True ↔ False) : False := h.mp trivial
+theorem false_of_true_eq_false  (h : True = False) : False := false_of_true_iff_false (Iff.of_eq h)
+
+theorem true_eq_false_of_false : False → (True = False) := False.elim
+
+theorem iff_def  : (a ↔ b) ↔ (a → b) ∧ (b → a) := iff_iff_implies_and_implies a b
+theorem iff_def' : (a ↔ b) ↔ (b → a) ∧ (a → b) := Iff.trans iff_def And.comm
+
+theorem true_iff_false : (True ↔ False) ↔ False := iff_false_intro (·.mp  True.intro)
+theorem false_iff_true : (False ↔ True) ↔ False := iff_false_intro (·.mpr True.intro)
+
+theorem iff_not_self : ¬(a ↔ ¬a) | H => let f h := H.1 h h; f (H.2 f)
+theorem heq_self_iff_true (a : α) : HEq a a ↔ True := iff_true_intro HEq.rfl
+
+/-! ## implies -/
+
+theorem not_not_of_not_imp : ¬(a → b) → ¬¬a := mt Not.elim
+
+theorem not_of_not_imp {a : Prop} : ¬(a → b) → ¬b := mt fun h _ => h
+
+@[simp] theorem imp_not_self : (a → ¬a) ↔ ¬a := Iff.intro (fun h ha => h ha ha) (fun h _ => h)
+
+theorem imp_intro {α β : Prop} (h : α) : β → α := fun _ => h
+
+theorem imp_imp_imp {a b c d : Prop} (h₀ : c → a) (h₁ : b → d) : (a → b) → (c → d) := (h₁ ∘ · ∘ h₀)
+
+theorem imp_iff_right {a : Prop} (ha : a) : (a → b) ↔ b := Iff.intro (· ha) (fun a _ => a)
+
+-- This is not marked `@[simp]` because we have `implies_true : (α → True) = True`
+theorem imp_true_iff (α : Sort u) : (α → True) ↔ True := iff_true_intro (fun _ => trivial)
+
+theorem false_imp_iff (a : Prop) : (False → a) ↔ True := iff_true_intro False.elim
+
+theorem true_imp_iff (α : Prop) : (True → α) ↔ α := imp_iff_right True.intro
+
+@[simp high] theorem imp_self : (a → a) ↔ True := iff_true_intro id
+
+@[simp] theorem imp_false : (a → False) ↔ ¬a := Iff.rfl
+
+theorem imp.swap : (a → b → c) ↔ (b → a → c) := Iff.intro flip flip
+
+theorem imp_not_comm : (a → ¬b) ↔ (b → ¬a) := imp.swap
+
+theorem imp_congr_left (h : a ↔ b) : (a → c) ↔ (b → c) := Iff.intro (· ∘ h.mpr) (· ∘ h.mp)
+
+theorem imp_congr_right (h : a → (b ↔ c)) : (a → b) ↔ (a → c) :=
+  Iff.intro (fun hab ha => (h ha).mp (hab ha)) (fun hcd ha => (h ha).mpr (hcd ha))
+
+theorem imp_congr_ctx (h₁ : a ↔ c) (h₂ : c → (b ↔ d)) : (a → b) ↔ (c → d) :=
+  Iff.trans (imp_congr_left h₁) (imp_congr_right h₂)
+
+theorem imp_congr (h₁ : a ↔ c) (h₂ : b ↔ d) : (a → b) ↔ (c → d) := imp_congr_ctx h₁ fun _ => h₂
+
+theorem imp_iff_not (hb : ¬b) : a → b ↔ ¬a := imp_congr_right fun _ => iff_false_intro hb
+
+/-! # Quotients -/
+
 namespace Quot
 /--
 The **quotient axiom**, or at least the nontrivial part of the quotient
@@ -1346,7 +1601,7 @@ protected def mk' {α : Sort u} [s : Setoid α] (a : α) : Quotient s :=
 The analogue of `Quot.sound`: If `a` and `b` are related by the equivalence relation,
 then they have equal equivalence classes.
 -/
-def sound {α : Sort u} {s : Setoid α} {a b : α} : a ≈ b → Quotient.mk s a = Quotient.mk s b :=
+theorem sound {α : Sort u} {s : Setoid α} {a b : α} : a ≈ b → Quotient.mk s a = Quotient.mk s b :=
   Quot.sound
 
 /--
@@ -1687,6 +1942,18 @@ axiom ofReduceNat (a b : Nat) (h : reduceNat a = b) : a = b
 
 end Lean
 
+@[simp] theorem ge_iff_le [LE α] {x y : α} : x ≥ y ↔ y ≤ x := Iff.rfl
+
+@[simp] theorem gt_iff_lt [LT α] {x y : α} : x > y ↔ y < x := Iff.rfl
+
+theorem le_of_eq_of_le {a b c : α} [LE α] (h₁ : a = b) (h₂ : b ≤ c) : a ≤ c := h₁ ▸ h₂
+
+theorem le_of_le_of_eq {a b c : α} [LE α] (h₁ : a ≤ b) (h₂ : b = c) : a ≤ c := h₂ ▸ h₁
+
+theorem lt_of_eq_of_lt {a b c : α} [LT α] (h₁ : a = b) (h₂ : b < c) : a < c := h₁ ▸ h₂
+
+theorem lt_of_lt_of_eq {a b c : α} [LT α] (h₁ : a < b) (h₂ : b = c) : a < c := h₂ ▸ h₁
+
 namespace Std
 variable {α : Sort u}
 

src/Init/Data.lean

@@ -6,11 +6,15 @@ Authors: Leonardo de Moura
 prelude
 import Init.Data.Basic
 import Init.Data.Nat
+import Init.Data.Bool
+import Init.Data.BitVec
+import Init.Data.Cast
 import Init.Data.Char
 import Init.Data.String
 import Init.Data.List
 import Init.Data.Int
 import Init.Data.Array
+import Init.Data.Array.Subarray.Split
 import Init.Data.ByteArray
 import Init.Data.FloatArray
 import Init.Data.Fin
@@ -29,3 +33,5 @@ import Init.Data.Prod
 import Init.Data.AC
 import Init.Data.Queue
 import Init.Data.Channel
+import Init.Data.Cast
+import Init.Data.Sum

src/Init/Data/AC.lean

@@ -106,7 +106,7 @@ def norm [info : ContextInformation α] (ctx : α) (e : Expr) : List Nat :=
   let xs := if info.isComm ctx then sort xs else xs
   if info.isIdem ctx then mergeIdem xs else xs
 
-theorem List.two_step_induction
+noncomputable def List.two_step_induction
   {motive : List Nat → Sort u}
   (l : List Nat)
   (empty : motive [])

src/Init/Data/Array.lean

@@ -11,3 +11,4 @@ import Init.Data.Array.InsertionSort
 import Init.Data.Array.DecidableEq
 import Init.Data.Array.Mem
 import Init.Data.Array.BasicAux
+import Init.Data.Array.Lemmas

src/Init/Data/Array/Basic.lean

@@ -10,7 +10,7 @@ import Init.Data.Fin.Basic
 import Init.Data.UInt.Basic
 import Init.Data.Repr
 import Init.Data.ToString.Basic
-import Init.Util
+import Init.GetElem
 universe u v w
 
 namespace Array
@@ -59,6 +59,8 @@ def uget (a : @& Array α) (i : USize) (h : i.toNat < a.size) : α :=
 instance : GetElem (Array α) USize α fun xs i => i.toNat < xs.size where
   getElem xs i h := xs.uget i h
 
+instance : LawfulGetElem (Array α) USize α fun xs i => i.toNat < xs.size where
+
 def back [Inhabited α] (a : Array α) : α :=
   a.get! (a.size - 1)
 
@@ -456,24 +458,12 @@ def findRev? {α : Type} (as : Array α) (p : α → Bool) : Option α :=
 
 @[inline]
 def findIdx? {α : Type u} (as : Array α) (p : α → Bool) : Option Nat :=
-  let rec loop (i : Nat) (j : Nat) (inv : i + j = as.size) : Option Nat :=
-    if hlt : j < as.size then
-      match i, inv with
-      | 0, inv => by
-        apply False.elim
-        rw [Nat.zero_add] at inv
-        rw [inv] at hlt
-        exact absurd hlt (Nat.lt_irrefl _)
-      | i+1, inv =>
-        if p as[j] then
-          some j
-        else
-          have : i + (j+1) = as.size := by
-            rw [← inv, Nat.add_comm j 1, Nat.add_assoc]
-          loop i (j+1) this
-    else
-      none
-  loop as.size 0 rfl
+  let rec loop (j : Nat) :=
+    if h : j < as.size then
+      if p as[j] then some j else loop (j + 1)
+    else none
+    termination_by as.size - j
+  loop 0
 
 def getIdx? [BEq α] (a : Array α) (v : α) : Option Nat :=
 a.findIdx? fun a => a == v
@@ -727,33 +717,36 @@ def takeWhile (p : α → Bool) (as : Array α) : Array α :=
     termination_by as.size - i
   go 0 #[]
 
-def eraseIdxAux (i : Nat) (a : Array α) : Array α :=
-  if h : i < a.size then
-    let idx  : Fin a.size := ⟨i, h⟩;
-    let idx1 : Fin a.size := ⟨i - 1, by exact Nat.lt_of_le_of_lt (Nat.pred_le i) h⟩;
-    let a' := a.swap idx idx1
-    eraseIdxAux (i+1) a'
+/-- Remove the element at a given index from an array without bounds checks, using a `Fin` index.
+
+  This function takes worst case O(n) time because
+  it has to backshift all elements at positions greater than `i`.-/
+def feraseIdx (a : Array α) (i : Fin a.size) : Array α :=
+  if h : i.val + 1 < a.size then
+    let a' := a.swap ⟨i.val + 1, h⟩ i
+    let i' : Fin a'.size := ⟨i.val + 1, by simp [a', h]⟩
+    have : a'.size - i' < a.size - i := by
+      simp [a', Nat.sub_succ_lt_self _ _ i.isLt]
+    a'.feraseIdx i'
   else
     a.pop
-termination_by a.size - i
+termination_by a.size - i.val
 
-def feraseIdx (a : Array α) (i : Fin a.size) : Array α :=
-  eraseIdxAux (i.val + 1) a
+theorem size_feraseIdx (a : Array α) (i : Fin a.size) : (a.feraseIdx i).size = a.size - 1 := by
+  induction a, i using Array.feraseIdx.induct with
+  | @case1 a i h a' _ _ ih =>
+    unfold feraseIdx
+    simp [h, a', ih]
+  | case2 a i h =>
+    unfold feraseIdx
+    simp [h]
 
+/-- Remove the element at a given index from an array, or do nothing if the index is out of bounds.
+
+  This function takes worst case O(n) time because
+  it has to backshift all elements at positions greater than `i`.-/
 def eraseIdx (a : Array α) (i : Nat) : Array α :=
-  if i < a.size then eraseIdxAux (i+1) a else a
-
-def eraseIdxSzAux (a : Array α) (i : Nat) (r : Array α) (heq : r.size = a.size) : { r : Array α // r.size = a.size - 1 } :=
-  if h : i < r.size then
-    let idx  : Fin r.size := ⟨i, h⟩;
-    let idx1 : Fin r.size := ⟨i - 1, by exact Nat.lt_of_le_of_lt (Nat.pred_le i) h⟩;
-    eraseIdxSzAux a (i+1) (r.swap idx idx1) ((size_swap r idx idx1).trans heq)
-  else
-    ⟨r.pop, (size_pop r).trans (heq ▸ rfl)⟩
-termination_by r.size - i
-
-def eraseIdx' (a : Array α) (i : Fin a.size) : { r : Array α // r.size = a.size - 1 } :=
-  eraseIdxSzAux a (i.val + 1) a rfl
+  if h : i < a.size then a.feraseIdx ⟨i, h⟩ else a
 
 def erase [BEq α] (as : Array α) (a : α) : Array α :=
   match as.indexOf? a with
@@ -809,7 +802,7 @@ where
     rfl
 
   go (i : Nat) (hi : i ≤ as.size) : toListLitAux as n hsz i hi (as.data.drop i) = as.data := by
-    cases i <;> simp [getLit_eq, List.get_drop_eq_drop, toListLitAux, List.drop, go]
+    induction i <;> simp [getLit_eq, List.get_drop_eq_drop, toListLitAux, List.drop, *]
 
 def isPrefixOfAux [BEq α] (as bs : Array α) (hle : as.size ≤ bs.size) (i : Nat) : Bool :=
   if h : i < as.size then

src/Init/Data/Array/DecidableEq.lean

@@ -5,7 +5,7 @@ Authors: Leonardo de Moura
 -/
 prelude
 import Init.Data.Array.Basic
-import Init.Classical
+import Init.ByCases
 
 namespace Array
 

src/Init/Data/Array/Lemmas.lean

@@ -0,0 +1,269 @@
+/-
+Copyright (c) 2022 Mario Carneiro. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Mario Carneiro
+-/
+prelude
+import Init.Data.Nat.MinMax
+import Init.Data.List.Lemmas
+import Init.Data.Fin.Basic
+import Init.Data.Array.Mem
+import Init.TacticsExtra
+
+/-!
+## Bootstrapping theorems about arrays
+
+This file contains some theorems about `Array` and `List` needed for `Std.List.Basic`.
+-/
+
+namespace Array
+
+attribute [simp] data_toArray uset
+
+@[simp] theorem mkEmpty_eq (α n) : @mkEmpty α n = #[] := rfl
+
+@[simp] theorem size_toArray (as : List α) : as.toArray.size = as.length := by simp [size]
+
+@[simp] theorem size_mk (as : List α) : (Array.mk as).size = as.length := by simp [size]
+
+theorem getElem_eq_data_get (a : Array α) (h : i < a.size) : a[i] = a.data.get ⟨i, h⟩ := by
+  by_cases i < a.size <;> (try simp [*]) <;> rfl
+
+theorem foldlM_eq_foldlM_data.aux [Monad m]
+    (f : β → α → m β) (arr : Array α) (i j) (H : arr.size ≤ i + j) (b) :
+    foldlM.loop f arr arr.size (Nat.le_refl _) i j b = (arr.data.drop j).foldlM f b := by
+  unfold foldlM.loop
+  split; split
+  · cases Nat.not_le_of_gt ‹_› (Nat.zero_add _ ▸ H)
+  · rename_i i; rw [Nat.succ_add] at H
+    simp [foldlM_eq_foldlM_data.aux f arr i (j+1) H]
+    rw (config := {occs := .pos [2]}) [← List.get_drop_eq_drop _ _ ‹_›]
+    rfl
+  · rw [List.drop_length_le (Nat.ge_of_not_lt ‹_›)]; rfl
+
+theorem foldlM_eq_foldlM_data [Monad m]
+    (f : β → α → m β) (init : β) (arr : Array α) :
+    arr.foldlM f init = arr.data.foldlM f init := by
+  simp [foldlM, foldlM_eq_foldlM_data.aux]
+
+theorem foldl_eq_foldl_data (f : β → α → β) (init : β) (arr : Array α) :
+    arr.foldl f init = arr.data.foldl f init :=
+  List.foldl_eq_foldlM .. ▸ foldlM_eq_foldlM_data ..
+
+theorem foldrM_eq_reverse_foldlM_data.aux [Monad m]
+    (f : α → β → m β) (arr : Array α) (init : β) (i h) :
+    (arr.data.take i).reverse.foldlM (fun x y => f y x) init = foldrM.fold f arr 0 i h init := by
+  unfold foldrM.fold
+  match i with
+  | 0 => simp [List.foldlM, List.take]
+  | i+1 => rw [← List.take_concat_get _ _ h]; simp [← (aux f arr · i)]; rfl
+
+theorem foldrM_eq_reverse_foldlM_data [Monad m] (f : α → β → m β) (init : β) (arr : Array α) :
+    arr.foldrM f init = arr.data.reverse.foldlM (fun x y => f y x) init := by
+  have : arr = #[] ∨ 0 < arr.size :=
+    match arr with | ⟨[]⟩ => .inl rfl | ⟨a::l⟩ => .inr (Nat.zero_lt_succ _)
+  match arr, this with | _, .inl rfl => rfl | arr, .inr h => ?_
+  simp [foldrM, h, ← foldrM_eq_reverse_foldlM_data.aux, List.take_length]
+
+theorem foldrM_eq_foldrM_data [Monad m]
+    (f : α → β → m β) (init : β) (arr : Array α) :
+    arr.foldrM f init = arr.data.foldrM f init := by
+  rw [foldrM_eq_reverse_foldlM_data, List.foldlM_reverse]
+
+theorem foldr_eq_foldr_data (f : α → β → β) (init : β) (arr : Array α) :
+    arr.foldr f init = arr.data.foldr f init :=
+  List.foldr_eq_foldrM .. ▸ foldrM_eq_foldrM_data ..
+
+@[simp] theorem push_data (arr : Array α) (a : α) : (arr.push a).data = arr.data ++ [a] := by
+  simp [push, List.concat_eq_append]
+
+theorem foldrM_push [Monad m] (f : α → β → m β) (init : β) (arr : Array α) (a : α) :
+    (arr.push a).foldrM f init = f a init >>= arr.foldrM f := by
+  simp [foldrM_eq_reverse_foldlM_data, -size_push]
+
+@[simp] theorem foldrM_push' [Monad m] (f : α → β → m β) (init : β) (arr : Array α) (a : α) :
+    (arr.push a).foldrM f init (start := arr.size + 1) = f a init >>= arr.foldrM f := by
+  simp [← foldrM_push]
+
+theorem foldr_push (f : α → β → β) (init : β) (arr : Array α) (a : α) :
+    (arr.push a).foldr f init = arr.foldr f (f a init) := foldrM_push ..
+
+@[simp] theorem foldr_push' (f : α → β → β) (init : β) (arr : Array α) (a : α) :
+    (arr.push a).foldr f init (start := arr.size + 1) = arr.foldr f (f a init) := foldrM_push' ..
+
+@[simp] theorem toListAppend_eq (arr : Array α) (l) : arr.toListAppend l = arr.data ++ l := by
+  simp [toListAppend, foldr_eq_foldr_data]
+
+@[simp] theorem toList_eq (arr : Array α) : arr.toList = arr.data := by
+  simp [toList, foldr_eq_foldr_data]
+
+/-- A more efficient version of `arr.toList.reverse`. -/
+@[inline] def toListRev (arr : Array α) : List α := arr.foldl (fun l t => t :: l) []
+
+@[simp] theorem toListRev_eq (arr : Array α) : arr.toListRev = arr.data.reverse := by
+  rw [toListRev, foldl_eq_foldl_data, ← List.foldr_reverse, List.foldr_self]
+
+theorem get_push_lt (a : Array α) (x : α) (i : Nat) (h : i < a.size) :
+    have : i < (a.push x).size := by simp [*, Nat.lt_succ_of_le, Nat.le_of_lt]
+    (a.push x)[i] = a[i] := by
+  simp only [push, getElem_eq_data_get, List.concat_eq_append, List.get_append_left, h]
+
+@[simp] theorem get_push_eq (a : Array α) (x : α) : (a.push x)[a.size] = x := by
+  simp only [push, getElem_eq_data_get, List.concat_eq_append]
+  rw [List.get_append_right] <;> simp [getElem_eq_data_get, Nat.zero_lt_one]
+
+theorem get_push (a : Array α) (x : α) (i : Nat) (h : i < (a.push x).size) :
+    (a.push x)[i] = if h : i < a.size then a[i] else x := by
+  by_cases h' : i < a.size
+  · simp [get_push_lt, h']
+  · simp at h
+    simp [get_push_lt, Nat.le_antisymm (Nat.le_of_lt_succ h) (Nat.ge_of_not_lt h')]
+
+theorem mapM_eq_foldlM [Monad m] [LawfulMonad m] (f : α → m β) (arr : Array α) :
+    arr.mapM f = arr.foldlM (fun bs a => bs.push <$> f a) #[] := by
+  rw [mapM, aux, foldlM_eq_foldlM_data]; rfl
+where
+  aux (i r) :
+      mapM.map f arr i r = (arr.data.drop i).foldlM (fun bs a => bs.push <$> f a) r := by
+    unfold mapM.map; split
+    · rw [← List.get_drop_eq_drop _ i ‹_›]
+      simp [aux (i+1), map_eq_pure_bind]; rfl
+    · rw [List.drop_length_le (Nat.ge_of_not_lt ‹_›)]; rfl
+  termination_by arr.size - i
+
+@[simp] theorem map_data (f : α → β) (arr : Array α) : (arr.map f).data = arr.data.map f := by
+  rw [map, mapM_eq_foldlM]
+  apply congrArg data (foldl_eq_foldl_data (fun bs a => push bs (f a)) #[] arr) |>.trans
+  have H (l arr) : List.foldl (fun bs a => push bs (f a)) arr l = ⟨arr.data ++ l.map f⟩ := by
+    induction l generalizing arr <;> simp [*]
+  simp [H]
+
+@[simp] theorem size_map (f : α → β) (arr : Array α) : (arr.map f).size = arr.size := by
+  simp [size]
+
+@[simp] theorem pop_data (arr : Array α) : arr.pop.data = arr.data.dropLast := rfl
+
+@[simp] theorem append_eq_append (arr arr' : Array α) : arr.append arr' = arr ++ arr' := rfl
+
+@[simp] theorem append_data (arr arr' : Array α) :
+    (arr ++ arr').data = arr.data ++ arr'.data := by
+  rw [← append_eq_append]; unfold Array.append
+  rw [foldl_eq_foldl_data]
+  induction arr'.data generalizing arr <;> simp [*]
+
+@[simp] theorem appendList_eq_append
+    (arr : Array α) (l : List α) : arr.appendList l = arr ++ l := rfl
+
+@[simp] theorem appendList_data (arr : Array α) (l : List α) :
+    (arr ++ l).data = arr.data ++ l := by
+  rw [← appendList_eq_append]; unfold Array.appendList
+  induction l generalizing arr <;> simp [*]
+
+@[simp] theorem appendList_nil (arr : Array α) : arr ++ ([] : List α) = arr := Array.ext' (by simp)
+
+@[simp] theorem appendList_cons (arr : Array α) (a : α) (l : List α) :
+    arr ++ (a :: l) = arr.push a ++ l := Array.ext' (by simp)
+
+theorem foldl_data_eq_bind (l : List α) (acc : Array β)
+    (F : Array β → α → Array β) (G : α → List β)
+    (H : ∀ acc a, (F acc a).data = acc.data ++ G a) :
+    (l.foldl F acc).data = acc.data ++ l.bind G := by
+  induction l generalizing acc <;> simp [*, List.bind]
+
+theorem foldl_data_eq_map (l : List α) (acc : Array β) (G : α → β) :
+    (l.foldl (fun acc a => acc.push (G a)) acc).data = acc.data ++ l.map G := by
+  induction l generalizing acc <;> simp [*]
+
+theorem size_uset (a : Array α) (v i h) : (uset a i v h).size = a.size := by simp
+
+theorem anyM_eq_anyM_loop [Monad m] (p : α → m Bool) (as : Array α) (start stop) :
+    anyM p as start stop = anyM.loop p as (min stop as.size) (Nat.min_le_right ..) start := by
+  simp only [anyM, Nat.min_def]; split <;> rfl
+
+theorem anyM_stop_le_start [Monad m] (p : α → m Bool) (as : Array α) (start stop)
+    (h : min stop as.size ≤ start) : anyM p as start stop = pure false := by
+  rw [anyM_eq_anyM_loop, anyM.loop, dif_neg (Nat.not_lt.2 h)]
+
+theorem mem_def (a : α) (as : Array α) : a ∈ as ↔ a ∈ as.data :=
+  ⟨fun | .mk h => h, Array.Mem.mk⟩
+
+/-- # get -/
+@[simp] theorem get_eq_getElem (a : Array α) (i : Fin _) : a.get i = a[i.1] := rfl
+
+theorem getElem?_lt
+    (a : Array α) {i : Nat} (h : i < a.size) : a[i]? = some (a[i]) := dif_pos h
+
+theorem getElem?_ge
+    (a : Array α) {i : Nat} (h : i ≥ a.size) : a[i]? = none := dif_neg (Nat.not_lt_of_le h)
+
+@[simp] theorem get?_eq_getElem? (a : Array α) (i : Nat) : a.get? i = a[i]? := rfl
+
+theorem getElem?_len_le (a : Array α) {i : Nat} (h : a.size ≤ i) : a[i]? = none := by
+  simp [getElem?_ge, h]
+
+theorem getD_get? (a : Array α) (i : Nat) (d : α) :
+  Option.getD a[i]? d = if p : i < a.size then a[i]'p else d := by
+  if h : i < a.size then
+    simp [setD, h, getElem?]
+  else
+    have p : i ≥ a.size := Nat.le_of_not_gt h
+    simp [setD, getElem?_len_le _ p, h]
+
+@[simp] theorem getD_eq_get? (a : Array α) (n d) : a.getD n d = (a[n]?).getD d := by
+  simp only [getD, get_eq_getElem, get?_eq_getElem?]; split <;> simp [getD_get?, *]
+
+theorem get!_eq_getD [Inhabited α] (a : Array α) : a.get! n = a.getD n default := rfl
+
+@[simp] theorem get!_eq_getElem? [Inhabited α] (a : Array α) (i : Nat) : a.get! i = (a.get? i).getD default := by
+  by_cases p : i < a.size <;> simp [getD_get?, get!_eq_getD, p]
+
+/-- # set -/
+
+@[simp] theorem getElem_set_eq (a : Array α) (i : Fin a.size) (v : α) {j : Nat}
+      (eq : i.val = j) (p : j < (a.set i v).size) :
+    (a.set i v)[j]'p = v := by
+  simp [set, getElem_eq_data_get, ←eq]
+
+@[simp] theorem getElem_set_ne (a : Array α) (i : Fin a.size) (v : α) {j : Nat} (pj : j < (a.set i v).size)
+    (h : i.val ≠ j) : (a.set i v)[j]'pj = a[j]'(size_set a i v ▸ pj) := by
+  simp only [set, getElem_eq_data_get, List.get_set_ne _ h]
+
+theorem getElem_set (a : Array α) (i : Fin a.size) (v : α) (j : Nat)
+    (h : j < (a.set i v).size) :
+    (a.set i v)[j]'h = if i = j then v else a[j]'(size_set a i v ▸ h) := by
+  by_cases p : i.1 = j <;> simp [p]
+
+@[simp] theorem getElem?_set_eq (a : Array α) (i : Fin a.size) (v : α) :
+    (a.set i v)[i.1]? = v := by simp [getElem?_lt, i.2]
+
+@[simp] theorem getElem?_set_ne (a : Array α) (i : Fin a.size) {j : Nat} (v : α)
+    (ne : i.val ≠ j) : (a.set i v)[j]? = a[j]? := by
+  by_cases h : j < a.size <;> simp [getElem?_lt, getElem?_ge, Nat.ge_of_not_lt, ne, h]
+
+/- # setD -/
+
+@[simp] theorem set!_is_setD : @set! = @setD := rfl
+
+@[simp] theorem size_setD (a : Array α) (index : Nat) (val : α) :
+  (Array.setD a index val).size = a.size := by
+  if h : index < a.size  then
+    simp [setD, h]
+  else
+    simp [setD, h]
+
+@[simp] theorem getElem_setD_eq (a : Array α) {i : Nat} (v : α) (h : _) :
+  (setD a i v)[i]'h = v := by
+  simp at h
+  simp only [setD, h, dite_true, getElem_set, ite_true]
+
+@[simp]
+theorem getElem?_setD_eq (a : Array α) {i : Nat} (p : i < a.size) (v : α) : (a.setD i v)[i]? = some v := by
+  simp [getElem?_lt, p]
+
+/-- Simplifies a normal form from `get!` -/
+@[simp] theorem getD_get?_setD (a : Array α) (i : Nat) (v d : α) :
+  Option.getD (setD a i v)[i]? d = if i < a.size then v else d := by
+  by_cases h : i < a.size <;>
+    simp [setD, Nat.not_lt_of_le, h,  getD_get?]
+
+end Array

src/Init/Data/Array/Mem.lean

@@ -8,16 +8,6 @@ import Init.Data.Array.Basic
 import Init.Data.Nat.Linear
 import Init.Data.List.BasicAux
 
-theorem List.sizeOf_get_lt [SizeOf α] (as : List α) (i : Fin as.length) : sizeOf (as.get i) < sizeOf as := by
-  match as, i with
-  | [],    i      => apply Fin.elim0 i
-  | a::as, ⟨0, _⟩ => simp_arith [get]
-  | a::as, ⟨i+1, h⟩ =>
-    simp [get]
-    have h : i < as.length := Nat.lt_of_succ_lt_succ h
-    have ih := sizeOf_get_lt as ⟨i, h⟩
-    exact Nat.lt_of_lt_of_le ih (Nat.le_add_left ..)
-
 namespace Array
 
 /-- `a ∈ as` is a predicate which asserts that `a` is in the array `as`. -/
@@ -29,10 +19,6 @@ structure Mem (a : α) (as : Array α) : Prop where
 instance : Membership α (Array α) where
   mem a as := Mem a as
 
-theorem sizeOf_get_lt [SizeOf α] (as : Array α) (i : Fin as.size) : sizeOf (as.get i) < sizeOf as := by
-  cases as with | _ as =>
-  exact Nat.lt_trans (List.sizeOf_get_lt as i) (by simp_arith)
-
 theorem sizeOf_lt_of_mem [SizeOf α] {as : Array α} (h : a ∈ as) : sizeOf a < sizeOf as := by
   cases as with | _ as =>
   exact Nat.lt_trans (List.sizeOf_lt_of_mem h.val) (by simp_arith)

src/Init/Data/Array/QSort.lean

@@ -10,7 +10,7 @@ namespace Array
 -- TODO: remove the [Inhabited α] parameters as soon as we have the tactic framework for automating proof generation and using Array.fget
 
 def qpartition (as : Array α) (lt : α → α → Bool) (lo hi : Nat) : Nat × Array α :=
-  if h : as.size = 0 then (0, as) else have : Inhabited α := ⟨as[0]'(by revert h; cases as.size <;> simp [Nat.zero_lt_succ])⟩ -- TODO: remove
+  if h : as.size = 0 then (0, as) else have : Inhabited α := ⟨as[0]'(by revert h; cases as.size <;> simp)⟩ -- TODO: remove
   let mid := (lo + hi) / 2
   let as  := if lt (as.get! mid) (as.get! lo) then as.swap! lo mid else as
   let as  := if lt (as.get! hi)  (as.get! lo) then as.swap! lo hi  else as

src/Init/Data/Array/Subarray.lean

@@ -9,29 +9,46 @@ import Init.Data.Array.Basic
 universe u v w
 
 structure Subarray (α : Type u)  where
-  as : Array α
+  array : Array α
   start : Nat
   stop : Nat
-  h₁ : start ≤ stop
-  h₂ : stop ≤ as.size
+  start_le_stop : start ≤ stop
+  stop_le_array_size : stop ≤ array.size
+
+@[deprecated Subarray.array]
+abbrev Subarray.as (s : Subarray α) : Array α := s.array
+
+@[deprecated Subarray.start_le_stop]
+theorem Subarray.h₁ (s : Subarray α) : s.start ≤ s.stop := s.start_le_stop
+
+@[deprecated Subarray.stop_le_array_size]
+theorem Subarray.h₂ (s : Subarray α) : s.stop ≤ s.as.size := s.stop_le_array_size
 
 namespace Subarray
 
 def size (s : Subarray α) : Nat :=
   s.stop - s.start
 
+theorem size_le_array_size {s : Subarray α} : s.size ≤ s.array.size := by
+  let {array, start, stop, start_le_stop, stop_le_array_size} := s
+  simp [size]
+  apply Nat.le_trans (Nat.sub_le stop start)
+  assumption
+
 def get (s : Subarray α) (i : Fin s.size) : α :=
-  have : s.start + i.val < s.as.size := by
-   apply Nat.lt_of_lt_of_le _ s.h₂
+  have : s.start + i.val < s.array.size := by
+   apply Nat.lt_of_lt_of_le _ s.stop_le_array_size
    have := i.isLt
    simp [size] at this
    rw [Nat.add_comm]
    exact Nat.add_lt_of_lt_sub this
-  s.as[s.start + i.val]
+  s.array[s.start + i.val]
 
 instance : GetElem (Subarray α) Nat α fun xs i => i < xs.size where
   getElem xs i h := xs.get ⟨i, h⟩
 
+instance : LawfulGetElem (Subarray α) Nat α fun xs i => i < xs.size where
+
 @[inline] def getD (s : Subarray α) (i : Nat) (v₀ : α) : α :=
   if h : i < s.size then s.get ⟨i, h⟩ else v₀
 
@@ -40,7 +57,7 @@ abbrev get! [Inhabited α] (s : Subarray α) (i : Nat) : α :=
 
 def popFront (s : Subarray α) : Subarray α :=
   if h : s.start < s.stop then
-    { s with start := s.start + 1, h₁ := Nat.le_of_lt_succ (Nat.add_lt_add_right h 1) }
+    { s with start := s.start + 1, start_le_stop := Nat.le_of_lt_succ (Nat.add_lt_add_right h 1) }
   else
     s
 
@@ -48,7 +65,7 @@ def popFront (s : Subarray α) : Subarray α :=
   let sz := USize.ofNat s.stop
   let rec @[specialize] loop (i : USize) (b : β) : m β := do
     if i < sz then
-      let a := s.as.uget i lcProof
+      let a := s.array.uget i lcProof
       match (← f a b) with
       | ForInStep.done  b => pure b
       | ForInStep.yield b => loop (i+1) b
@@ -66,27 +83,27 @@ instance : ForIn m (Subarray α) α where
 
 @[inline]
 def foldlM {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m] (f : β → α → m β) (init : β) (as : Subarray α) : m β :=
-  as.as.foldlM f (init := init) (start := as.start) (stop := as.stop)
+  as.array.foldlM f (init := init) (start := as.start) (stop := as.stop)
 
 @[inline]
 def foldrM {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m] (f : α → β → m β) (init : β) (as : Subarray α) : m β :=
-  as.as.foldrM f (init := init) (start := as.stop) (stop := as.start)
+  as.array.foldrM f (init := init) (start := as.stop) (stop := as.start)
 
 @[inline]
 def anyM {α : Type u} {m : Type → Type w} [Monad m] (p : α → m Bool) (as : Subarray α) : m Bool :=
-  as.as.anyM p (start := as.start) (stop := as.stop)
+  as.array.anyM p (start := as.start) (stop := as.stop)
 
 @[inline]
 def allM {α : Type u} {m : Type → Type w} [Monad m] (p : α → m Bool) (as : Subarray α) : m Bool :=
-  as.as.allM p (start := as.start) (stop := as.stop)
+  as.array.allM p (start := as.start) (stop := as.stop)
 
 @[inline]
 def forM {α : Type u} {m : Type v → Type w} [Monad m] (f : α → m PUnit) (as : Subarray α) : m PUnit :=
-  as.as.forM f (start := as.start) (stop := as.stop)
+  as.array.forM f (start := as.start) (stop := as.stop)
 
 @[inline]
 def forRevM {α : Type u} {m : Type v → Type w} [Monad m] (f : α → m PUnit) (as : Subarray α) : m PUnit :=
-  as.as.forRevM f (start := as.stop) (stop := as.start)
+  as.array.forRevM f (start := as.stop) (stop := as.start)
 
 @[inline]
 def foldl {α : Type u} {β : Type v} (f : β → α → β) (init : β) (as : Subarray α) : β :=
@@ -133,16 +150,27 @@ variable {α : Type u}
 
 def toSubarray (as : Array α) (start : Nat := 0) (stop : Nat := as.size) : Subarray α :=
   if h₂ : stop ≤ as.size then
-     if h₁ : start ≤ stop then
-       { as := as, start := start, stop := stop, h₁ := h₁, h₂ := h₂ }
-     else
-       { as := as, start := stop, stop := stop, h₁ := Nat.le_refl _, h₂ := h₂ }
+    if h₁ : start ≤ stop then
+      { array := as, start := start, stop := stop,
+        start_le_stop := h₁, stop_le_array_size := h₂ }
+    else
+      { array := as, start := stop, stop := stop,
+        start_le_stop := Nat.le_refl _, stop_le_array_size := h₂ }
   else
-     if h₁ : start ≤ as.size then
-       { as := as, start := start, stop := as.size, h₁ := h₁, h₂ := Nat.le_refl _ }
-     else
-       { as := as, start := as.size, stop := as.size, h₁ := Nat.le_refl _, h₂ := Nat.le_refl _ }
+    if h₁ : start ≤ as.size then
+      { array := as,
+        start := start,
+        stop := as.size,
+        start_le_stop := h₁,
+        stop_le_array_size := Nat.le_refl _ }
+    else
+      { array := as,
+        start := as.size,
+        stop := as.size,
+        start_le_stop := Nat.le_refl _,
+        stop_le_array_size := Nat.le_refl _ }
 
+@[coe]
 def ofSubarray (s : Subarray α) : Array α := Id.run do
   let mut as := mkEmpty (s.stop - s.start)
   for a in s do

src/Init/Data/Array/Subarray/Split.lean

@@ -0,0 +1,71 @@
+/-
+Copyright (c) 2024 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: David Thrane Christiansen
+-/
+
+prelude
+import Init.Data.Array.Basic
+import Init.Data.Array.Subarray
+import Init.Omega
+
+/-
+This module contains splitting operations on subarrays that crucially rely on `omega` for proof
+automation. Placing them in another module breaks an import cycle, because `omega` itself uses the
+array library.
+-/
+
+namespace Subarray
+/--
+Splits a subarray into two parts.
+-/
+def split (s : Subarray α) (i : Fin s.size.succ) : (Subarray α × Subarray α) :=
+  let ⟨i', isLt⟩ := i
+  have := s.start_le_stop
+  have := s.stop_le_array_size
+  have : i' ≤ s.stop - s.start := Nat.lt_succ.mp isLt
+  have : s.start + i' ≤ s.stop := by omega
+  have : s.start + i' ≤ s.array.size := by omega
+  have : s.start + i' ≤ s.stop := by
+    simp only [size] at isLt
+    omega
+  let pre := {s with
+    stop := s.start + i',
+    start_le_stop := by omega,
+    stop_le_array_size := by assumption
+  }
+  let post := {s with
+    start := s.start + i'
+    start_le_stop := by assumption
+  }
+  (pre, post)
+
+/--
+Removes the first `i` elements of the subarray. If there are `i` or fewer elements, the resulting
+subarray is empty.
+-/
+def drop (arr : Subarray α) (i : Nat) : Subarray α where
+  array := arr.array
+  start := min (arr.start + i) arr.stop
+  stop := arr.stop
+  start_le_stop := by
+    rw [Nat.min_def]
+    split <;> simp only [Nat.le_refl, *]
+  stop_le_array_size := arr.stop_le_array_size
+
+/--
+Keeps only the first `i` elements of the subarray. If there are `i` or fewer elements, the resulting
+subarray is empty.
+-/
+def take (arr : Subarray α) (i : Nat) : Subarray α where
+  array := arr.array
+  start := arr.start
+  stop := min (arr.start + i) arr.stop
+  start_le_stop := by
+    have := arr.start_le_stop
+    rw [Nat.min_def]
+    split <;> omega
+  stop_le_array_size := by
+    have := arr.stop_le_array_size
+    rw [Nat.min_def]
+    split <;> omega

src/Init/Data/BitVec.lean

@@ -0,0 +1,10 @@
+/-
+Copyright (c) 2024 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Scott Morrison
+-/
+prelude
+import Init.Data.BitVec.Basic
+import Init.Data.BitVec.Bitblast
+import Init.Data.BitVec.Folds
+import Init.Data.BitVec.Lemmas

src/Init/Data/BitVec/Basic.lean

@@ -0,0 +1,631 @@
+/-
+Copyright (c) 2024 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Joe Hendrix, Wojciech Nawrocki, Leonardo de Moura, Mario Carneiro, Alex Keizer, Harun Khan, Abdalrhman M Mohamed
+-/
+prelude
+import Init.Data.Fin.Basic
+import Init.Data.Nat.Bitwise.Lemmas
+import Init.Data.Nat.Power2
+import Init.Data.Int.Bitwise
+
+/-!
+We define bitvectors. We choose the `Fin` representation over others for its relative efficiency
+(Lean has special support for `Nat`), alignment with `UIntXY` types which are also represented
+with `Fin`, and the fact that bitwise operations on `Fin` are already defined. Some other possible
+representations are `List Bool`, `{ l : List Bool // l.length = w }`, `Fin w → Bool`.
+
+We define many of the bitvector operations from the
+[`QF_BV` logic](https://smtlib.cs.uiowa.edu/logics-all.shtml#QF_BV).
+of SMT-LIBv2.
+-/
+
+/--
+A bitvector of the specified width.
+
+This is represented as the underlying `Nat` number in both the runtime
+and the kernel, inheriting all the special support for `Nat`.
+-/
+structure BitVec (w : Nat) where
+  /-- Construct a `BitVec w` from a number less than `2^w`.
+  O(1), because we use `Fin` as the internal representation of a bitvector. -/
+  ofFin ::
+  /-- Interpret a bitvector as a number less than `2^w`.
+  O(1), because we use `Fin` as the internal representation of a bitvector. -/
+  toFin : Fin (2^w)
+
+@[deprecated] protected abbrev Std.BitVec := _root_.BitVec
+
+-- We manually derive the `DecidableEq` instances for `BitVec` because
+-- we want to have builtin support for bit-vector literals, and we
+-- need a name for this function to implement `canUnfoldAtMatcher` at `WHNF.lean`.
+def BitVec.decEq (a b : BitVec n) : Decidable (a = b) :=
+  match a, b with
+  | ⟨n⟩, ⟨m⟩ =>
+    if h : n = m then
+      isTrue (h ▸ rfl)
+    else
+      isFalse (fun h' => BitVec.noConfusion h' (fun h' => absurd h' h))
+
+instance : DecidableEq (BitVec n) := BitVec.decEq
+
+namespace BitVec
+
+section Nat
+
+/-- The `BitVec` with value `i`, given a proof that `i < 2^n`. -/
+@[match_pattern]
+protected def ofNatLt {n : Nat} (i : Nat) (p : i < 2^n) : BitVec n where
+  toFin := ⟨i, p⟩
+
+/-- The `BitVec` with value `i mod 2^n`. -/
+@[match_pattern]
+protected def ofNat (n : Nat) (i : Nat) : BitVec n where
+  toFin := Fin.ofNat' i (Nat.two_pow_pos n)
+
+instance instOfNat : OfNat (BitVec n) i where ofNat := .ofNat n i
+instance natCastInst : NatCast (BitVec w) := ⟨BitVec.ofNat w⟩
+
+/-- Given a bitvector `a`, return the underlying `Nat`. This is O(1) because `BitVec` is a
+(zero-cost) wrapper around a `Nat`. -/
+protected def toNat (a : BitVec n) : Nat := a.toFin.val
+
+/-- Return the bound in terms of toNat. -/
+theorem isLt (x : BitVec w) : x.toNat < 2^w := x.toFin.isLt
+
+@[deprecated isLt]
+theorem toNat_lt (x : BitVec n) : x.toNat < 2^n := x.isLt
+
+/-- Theorem for normalizing the bit vector literal representation. -/
+-- TODO: This needs more usage data to assess which direction the simp should go.
+@[simp, bv_toNat] theorem ofNat_eq_ofNat : @OfNat.ofNat (BitVec n) i _ = .ofNat n i := rfl
+
+-- Note. Mathlib would like this to go the other direction.
+@[simp] theorem natCast_eq_ofNat (w x : Nat) : @Nat.cast (BitVec w) _ x = .ofNat w x := rfl
+
+end Nat
+
+section subsingleton
+
+/-- All empty bitvectors are equal -/
+instance : Subsingleton (BitVec 0) where
+  allEq := by intro ⟨0, _⟩ ⟨0, _⟩; rfl
+
+/-- The empty bitvector -/
+abbrev nil : BitVec 0 := 0
+
+/-- Every bitvector of length 0 is equal to `nil`, i.e., there is only one empty bitvector -/
+theorem eq_nil (x : BitVec 0) : x = nil := Subsingleton.allEq ..
+
+end subsingleton
+
+section zero_allOnes
+
+/-- Return a bitvector `0` of size `n`. This is the bitvector with all zero bits. -/
+protected def zero (n : Nat) : BitVec n := .ofNatLt 0 (Nat.two_pow_pos n)
+instance : Inhabited (BitVec n) where default := .zero n
+
+/-- Bit vector of size `n` where all bits are `1`s -/
+def allOnes (n : Nat) : BitVec n :=
+  .ofNatLt (2^n - 1) (Nat.le_of_eq (Nat.sub_add_cancel (Nat.two_pow_pos n)))
+
+end zero_allOnes
+
+section getXsb
+
+/-- Return the `i`-th least significant bit or `false` if `i ≥ w`. -/
+@[inline] def getLsb (x : BitVec w) (i : Nat) : Bool := x.toNat.testBit i
+
+/-- Return the `i`-th most significant bit or `false` if `i ≥ w`. -/
+@[inline] def getMsb (x : BitVec w) (i : Nat) : Bool := i < w && getLsb x (w-1-i)
+
+/-- Return most-significant bit in bitvector. -/
+@[inline] protected def msb (a : BitVec n) : Bool := getMsb a 0
+
+end getXsb
+
+section Int
+
+/-- Interpret the bitvector as an integer stored in two's complement form. -/
+protected def toInt (a : BitVec n) : Int :=
+  if 2 * a.toNat < 2^n then
+    a.toNat
+  else
+    (a.toNat : Int) - (2^n : Nat)
+
+/-- The `BitVec` with value `(2^n + (i mod 2^n)) mod 2^n`.  -/
+protected def ofInt (n : Nat) (i : Int) : BitVec n := .ofNatLt (i % (Int.ofNat (2^n))).toNat (by
+  apply (Int.toNat_lt _).mpr
+  · apply Int.emod_lt_of_pos
+    exact Int.ofNat_pos.mpr (Nat.two_pow_pos _)
+  · apply Int.emod_nonneg
+    intro eq
+    apply Nat.ne_of_gt (Nat.two_pow_pos n)
+    exact Int.ofNat_inj.mp eq)
+
+instance : IntCast (BitVec w) := ⟨BitVec.ofInt w⟩
+
+end Int
+
+section Syntax
+
+/-- Notation for bit vector literals. `i#n` is a shorthand for `BitVec.ofNat n i`. -/
+scoped syntax:max term:max noWs "#" noWs term:max : term
+macro_rules | `($i#$n) => `(BitVec.ofNat $n $i)
+
+/-- Unexpander for bit vector literals. -/
+@[app_unexpander BitVec.ofNat] def unexpandBitVecOfNat : Lean.PrettyPrinter.Unexpander
+  | `($(_) $n $i) => `($i#$n)
+  | _ => throw ()
+
+/-- Notation for bit vector literals without truncation. `i#'lt` is a shorthand for `BitVec.ofNatLt i lt`. -/
+scoped syntax:max term:max noWs "#'" noWs term:max : term
+macro_rules | `($i#'$p) => `(BitVec.ofNatLt $i $p)
+
+/-- Unexpander for bit vector literals without truncation. -/
+@[app_unexpander BitVec.ofNatLt] def unexpandBitVecOfNatLt : Lean.PrettyPrinter.Unexpander
+  | `($(_) $i $p) => `($i#'$p)
+  | _ => throw ()
+
+end Syntax
+
+section repr_toString
+
+/-- Convert bitvector into a fixed-width hex number. -/
+protected def toHex {n : Nat} (x : BitVec n) : String :=
+  let s := (Nat.toDigits 16 x.toNat).asString
+  let t := (List.replicate ((n+3) / 4 - s.length) '0').asString
+  t ++ s
+
+instance : Repr (BitVec n) where reprPrec a _ := "0x" ++ (a.toHex : Std.Format) ++ "#" ++ repr n
+instance : ToString (BitVec n) where toString a := toString (repr a)
+
+end repr_toString
+
+section arithmetic
+
+/--
+Addition for bit vectors. This can be interpreted as either signed or unsigned addition
+modulo `2^n`.
+
+SMT-Lib name: `bvadd`.
+-/
+protected def add (x y : BitVec n) : BitVec n := .ofNat n (x.toNat + y.toNat)
+instance : Add (BitVec n) := ⟨BitVec.add⟩
+
+/--
+Subtraction for bit vectors. This can be interpreted as either signed or unsigned subtraction
+modulo `2^n`.
+-/
+protected def sub (x y : BitVec n) : BitVec n := .ofNat n (x.toNat + (2^n - y.toNat))
+instance : Sub (BitVec n) := ⟨BitVec.sub⟩
+
+/--
+Negation for bit vectors. This can be interpreted as either signed or unsigned negation
+modulo `2^n`.
+
+SMT-Lib name: `bvneg`.
+-/
+protected def neg (x : BitVec n) : BitVec n := .ofNat n (2^n - x.toNat)
+instance : Neg (BitVec n) := ⟨.neg⟩
+
+/--
+Return the absolute value of a signed bitvector.
+-/
+protected def abs (s : BitVec n) : BitVec n := if s.msb then .neg s else s
+
+/--
+Multiplication for bit vectors. This can be interpreted as either signed or unsigned negation
+modulo `2^n`.
+
+SMT-Lib name: `bvmul`.
+-/
+protected def mul (x y : BitVec n) : BitVec n := BitVec.ofNat n (x.toNat * y.toNat)
+instance : Mul (BitVec n) := ⟨.mul⟩
+
+/--
+Unsigned division for bit vectors using the Lean convention where division by zero returns zero.
+-/
+def udiv (x y : BitVec n) : BitVec n :=
+  (x.toNat / y.toNat)#'(Nat.lt_of_le_of_lt (Nat.div_le_self _ _) x.isLt)
+instance : Div (BitVec n) := ⟨.udiv⟩
+
+/--
+Unsigned modulo for bit vectors.
+
+SMT-Lib name: `bvurem`.
+-/
+def umod (x y : BitVec n) : BitVec n :=
+  (x.toNat % y.toNat)#'(Nat.lt_of_le_of_lt (Nat.mod_le _ _) x.isLt)
+instance : Mod (BitVec n) := ⟨.umod⟩
+
+/--
+Unsigned division for bit vectors using the
+[SMT-Lib convention](http://smtlib.cs.uiowa.edu/theories-FixedSizeBitVectors.shtml)
+where division by zero returns the `allOnes` bitvector.
+
+SMT-Lib name: `bvudiv`.
+-/
+def smtUDiv (x y : BitVec n) : BitVec n := if y = 0 then allOnes n else udiv x y
+
+/--
+Signed t-division for bit vectors using the Lean convention where division
+by zero returns zero.
+
+```lean
+sdiv 7#4 2 = 3#4
+sdiv (-9#4) 2 = -4#4
+sdiv 5#4 -2 = -2#4
+sdiv (-7#4) (-2) = 3#4
+```
+-/
+def sdiv (s t : BitVec n) : BitVec n :=
+  match s.msb, t.msb with
+  | false, false => udiv s t
+  | false, true  => .neg (udiv s (.neg t))
+  | true,  false => .neg (udiv (.neg s) t)
+  | true,  true  => udiv (.neg s) (.neg t)
+
+/--
+Signed division for bit vectors using SMTLIB rules for division by zero.
+
+Specifically, `smtSDiv x 0 = if x >= 0 then -1 else 1`
+
+SMT-Lib name: `bvsdiv`.
+-/
+def smtSDiv (s t : BitVec n) : BitVec n :=
+  match s.msb, t.msb with
+  | false, false => smtUDiv s t
+  | false, true  => .neg (smtUDiv s (.neg t))
+  | true,  false => .neg (smtUDiv (.neg s) t)
+  | true,  true  => smtUDiv (.neg s) (.neg t)
+
+/--
+Remainder for signed division rounding to zero.
+
+SMT_Lib name: `bvsrem`.
+-/
+def srem (s t : BitVec n) : BitVec n :=
+  match s.msb, t.msb with
+  | false, false => umod s t
+  | false, true  => umod s (.neg t)
+  | true,  false => .neg (umod (.neg s) t)
+  | true,  true  => .neg (umod (.neg s) (.neg t))
+
+/--
+Remainder for signed division rounded to negative infinity.
+
+SMT_Lib name: `bvsmod`.
+-/
+def smod (s t : BitVec m) : BitVec m :=
+  match s.msb, t.msb with
+  | false, false => umod s t
+  | false, true =>
+    let u := umod s (.neg t)
+    (if u = .zero m then u else .add u t)
+  | true, false =>
+    let u := umod (.neg s) t
+    (if u = .zero m then u else .sub t u)
+  | true, true => .neg (umod (.neg s) (.neg t))
+
+end arithmetic
+
+
+section bool
+
+/-- Turn a `Bool` into a bitvector of length `1` -/
+def ofBool (b : Bool) : BitVec 1 := cond b 1 0
+
+@[simp] theorem ofBool_false : ofBool false = 0 := by trivial
+@[simp] theorem ofBool_true  : ofBool true  = 1 := by trivial
+
+/-- Fills a bitvector with `w` copies of the bit `b`. -/
+def fill (w : Nat) (b : Bool) : BitVec w := bif b then -1 else 0
+
+end bool
+
+section relations
+
+/--
+Unsigned less-than for bit vectors.
+
+SMT-Lib name: `bvult`.
+-/
+protected def ult (x y : BitVec n) : Bool := x.toNat < y.toNat
+
+instance : LT (BitVec n) where lt := (·.toNat < ·.toNat)
+instance (x y : BitVec n) : Decidable (x < y) :=
+  inferInstanceAs (Decidable (x.toNat < y.toNat))
+
+/--
+Unsigned less-than-or-equal-to for bit vectors.
+
+SMT-Lib name: `bvule`.
+-/
+protected def ule (x y : BitVec n) : Bool := x.toNat ≤ y.toNat
+
+instance : LE (BitVec n) where le := (·.toNat ≤ ·.toNat)
+instance (x y : BitVec n) : Decidable (x ≤ y) :=
+  inferInstanceAs (Decidable (x.toNat ≤ y.toNat))
+
+/--
+Signed less-than for bit vectors.
+
+```lean
+BitVec.slt 6#4 7 = true
+BitVec.slt 7#4 8 = false
+```
+SMT-Lib name: `bvslt`.
+-/
+protected def slt (x y : BitVec n) : Bool := x.toInt < y.toInt
+
+/--
+Signed less-than-or-equal-to for bit vectors.
+
+SMT-Lib name: `bvsle`.
+-/
+protected def sle (x y : BitVec n) : Bool := x.toInt ≤ y.toInt
+
+end relations
+
+section cast
+
+/-- `cast eq i` embeds `i` into an equal `BitVec` type. -/
+@[inline] def cast (eq : n = m) (i : BitVec n) : BitVec m := .ofNatLt i.toNat (eq ▸ i.isLt)
+
+@[simp] theorem cast_ofNat {n m : Nat} (h : n = m) (x : Nat) :
+    cast h (BitVec.ofNat n x) = BitVec.ofNat m x := by
+  subst h; rfl
+
+@[simp] theorem cast_cast {n m k : Nat} (h₁ : n = m) (h₂ : m = k) (x : BitVec n) :
+    cast h₂ (cast h₁ x) = cast (h₁ ▸ h₂) x :=
+  rfl
+
+@[simp] theorem cast_eq {n : Nat} (h : n = n) (x : BitVec n) : cast h x = x := rfl
+
+/--
+Extraction of bits `start` to `start + len - 1` from a bit vector of size `n` to yield a
+new bitvector of size `len`. If `start + len > n`, then the vector will be zero-padded in the
+high bits.
+-/
+def extractLsb' (start len : Nat) (a : BitVec n) : BitVec len := .ofNat _ (a.toNat >>> start)
+
+/--
+Extraction of bits `hi` (inclusive) down to `lo` (inclusive) from a bit vector of size `n` to
+yield a new bitvector of size `hi - lo + 1`.
+
+SMT-Lib name: `extract`.
+-/
+def extractLsb (hi lo : Nat) (a : BitVec n) : BitVec (hi - lo + 1) := extractLsb' lo _ a
+
+/--
+A version of `zeroExtend` that requires a proof, but is a noop.
+-/
+def zeroExtend' {n w : Nat} (le : n ≤ w) (x : BitVec n)  : BitVec w :=
+  x.toNat#'(by
+    apply Nat.lt_of_lt_of_le x.isLt
+    exact Nat.pow_le_pow_of_le_right (by trivial) le)
+
+/--
+`shiftLeftZeroExtend x n` returns `zeroExtend (w+n) x <<< n` without
+needing to compute `x % 2^(2+n)`.
+-/
+def shiftLeftZeroExtend (msbs : BitVec w) (m : Nat) : BitVec (w+m) :=
+  let shiftLeftLt {x : Nat} (p : x < 2^w) (m : Nat) : x <<< m < 2^(w+m) := by
+        simp [Nat.shiftLeft_eq, Nat.pow_add]
+        apply Nat.mul_lt_mul_of_pos_right p
+        exact (Nat.two_pow_pos m)
+  (msbs.toNat <<< m)#'(shiftLeftLt msbs.isLt m)
+
+/--
+Zero extend vector `x` of length `w` by adding zeros in the high bits until it has length `v`.
+If `v < w` then it truncates the high bits instead.
+
+SMT-Lib name: `zero_extend`.
+-/
+def zeroExtend (v : Nat) (x : BitVec w) : BitVec v :=
+  if h : w ≤ v then
+    zeroExtend' h x
+  else
+    .ofNat v x.toNat
+
+/--
+Truncate the high bits of bitvector `x` of length `w`, resulting in a vector of length `v`.
+If `v > w` then it zero-extends the vector instead.
+-/
+abbrev truncate := @zeroExtend
+
+/--
+Sign extend a vector of length `w`, extending with `i` additional copies of the most significant
+bit in `x`. If `x` is an empty vector, then the sign is treated as zero.
+
+SMT-Lib name: `sign_extend`.
+-/
+def signExtend (v : Nat) (x : BitVec w) : BitVec v := .ofInt v x.toInt
+
+end cast
+
+section bitwise
+
+/--
+Bitwise AND for bit vectors.
+
+```lean
+0b1010#4 &&& 0b0110#4 = 0b0010#4
+```
+
+SMT-Lib name: `bvand`.
+-/
+protected def and (x y : BitVec n) : BitVec n :=
+  (x.toNat &&& y.toNat)#'(Nat.and_lt_two_pow x.toNat y.isLt)
+instance : AndOp (BitVec w) := ⟨.and⟩
+
+/--
+Bitwise OR for bit vectors.
+
+```lean
+0b1010#4 ||| 0b0110#4 = 0b1110#4
+```
+
+SMT-Lib name: `bvor`.
+-/
+protected def or (x y : BitVec n) : BitVec n :=
+  (x.toNat ||| y.toNat)#'(Nat.or_lt_two_pow x.isLt y.isLt)
+instance : OrOp (BitVec w) := ⟨.or⟩
+
+/--
+ Bitwise XOR for bit vectors.
+
+```lean
+0b1010#4 ^^^ 0b0110#4 = 0b1100#4
+```
+
+SMT-Lib name: `bvxor`.
+-/
+protected def xor (x y : BitVec n) : BitVec n :=
+  (x.toNat ^^^ y.toNat)#'(Nat.xor_lt_two_pow x.isLt y.isLt)
+instance : Xor (BitVec w) := ⟨.xor⟩
+
+/--
+Bitwise NOT for bit vectors.
+
+```lean
+~~~(0b0101#4) == 0b1010
+```
+SMT-Lib name: `bvnot`.
+-/
+protected def not (x : BitVec n) : BitVec n := allOnes n ^^^ x
+instance : Complement (BitVec w) := ⟨.not⟩
+
+/--
+Left shift for bit vectors. The low bits are filled with zeros. As a numeric operation, this is
+equivalent to `a * 2^s`, modulo `2^n`.
+
+SMT-Lib name: `bvshl` except this operator uses a `Nat` shift value.
+-/
+protected def shiftLeft (a : BitVec n) (s : Nat) : BitVec n := (a.toNat <<< s)#n
+instance : HShiftLeft (BitVec w) Nat (BitVec w) := ⟨.shiftLeft⟩
+
+/--
+(Logical) right shift for bit vectors. The high bits are filled with zeros.
+As a numeric operation, this is equivalent to `a / 2^s`, rounding down.
+
+SMT-Lib name: `bvlshr` except this operator uses a `Nat` shift value.
+-/
+def ushiftRight (a : BitVec n) (s : Nat) : BitVec n :=
+  (a.toNat >>> s)#'(by
+  let ⟨a, lt⟩ := a
+  simp only [BitVec.toNat, Nat.shiftRight_eq_div_pow, Nat.div_lt_iff_lt_mul (Nat.two_pow_pos s)]
+  rw [←Nat.mul_one a]
+  exact Nat.mul_lt_mul_of_lt_of_le' lt (Nat.two_pow_pos s) (Nat.le_refl 1))
+
+instance : HShiftRight (BitVec w) Nat (BitVec w) := ⟨.ushiftRight⟩
+
+/--
+Arithmetic right shift for bit vectors. The high bits are filled with the
+most-significant bit.
+As a numeric operation, this is equivalent to `a.toInt >>> s`.
+
+SMT-Lib name: `bvashr` except this operator uses a `Nat` shift value.
+-/
+def sshiftRight (a : BitVec n) (s : Nat) : BitVec n := .ofInt n (a.toInt >>> s)
+
+instance {n} : HShiftLeft  (BitVec m) (BitVec n) (BitVec m) := ⟨fun x y => x <<< y.toNat⟩
+instance {n} : HShiftRight (BitVec m) (BitVec n) (BitVec m) := ⟨fun x y => x >>> y.toNat⟩
+
+/--
+Rotate left for bit vectors. All the bits of `x` are shifted to higher positions, with the top `n`
+bits wrapping around to fill the low bits.
+
+```lean
+rotateLeft  0b0011#4 3 = 0b1001
+```
+SMT-Lib name: `rotate_left` except this operator uses a `Nat` shift amount.
+-/
+def rotateLeft (x : BitVec w) (n : Nat) : BitVec w := x <<< n ||| x >>> (w - n)
+
+/--
+Rotate right for bit vectors. All the bits of `x` are shifted to lower positions, with the
+bottom `n` bits wrapping around to fill the high bits.
+
+```lean
+rotateRight 0b01001#5 1 = 0b10100
+```
+SMT-Lib name: `rotate_right` except this operator uses a `Nat` shift amount.
+-/
+def rotateRight (x : BitVec w) (n : Nat) : BitVec w := x >>> n ||| x <<< (w - n)
+
+/--
+Concatenation of bitvectors. This uses the "big endian" convention that the more significant
+input is on the left, so `0xAB#8 ++ 0xCD#8 = 0xABCD#16`.
+
+SMT-Lib name: `concat`.
+-/
+def append (msbs : BitVec n) (lsbs : BitVec m) : BitVec (n+m) :=
+  shiftLeftZeroExtend msbs m ||| zeroExtend' (Nat.le_add_left m n) lsbs
+
+instance : HAppend (BitVec w) (BitVec v) (BitVec (w + v)) := ⟨.append⟩
+
+-- TODO: write this using multiplication
+/-- `replicate i x` concatenates `i` copies of `x` into a new vector of length `w*i`. -/
+def replicate : (i : Nat) → BitVec w → BitVec (w*i)
+  | 0,   _ => 0
+  | n+1, x =>
+    have hEq : w + w*n = w*(n + 1) := by
+      rw [Nat.mul_add, Nat.add_comm, Nat.mul_one]
+    hEq ▸ (x ++ replicate n x)
+
+/-!
+### Cons and Concat
+We give special names to the operations of adding a single bit to either end of a bitvector.
+We follow the precedent of `Vector.cons`/`Vector.concat` both for the name, and for the decision
+to have the resulting size be `n + 1` for both operations (rather than `1 + n`, which would be the
+result of appending a single bit to the front in the naive implementation).
+-/
+
+/-- Append a single bit to the end of a bitvector, using big endian order (see `append`).
+    That is, the new bit is the least significant bit. -/
+def concat {n} (msbs : BitVec n) (lsb : Bool) : BitVec (n+1) := msbs ++ (ofBool lsb)
+
+/-- Prepend a single bit to the front of a bitvector, using big endian order (see `append`).
+    That is, the new bit is the most significant bit. -/
+def cons {n} (msb : Bool) (lsbs : BitVec n) : BitVec (n+1) :=
+  ((ofBool msb) ++ lsbs).cast (Nat.add_comm ..)
+
+theorem append_ofBool (msbs : BitVec w) (lsb : Bool) :
+    msbs ++ ofBool lsb = concat msbs lsb :=
+  rfl
+
+theorem ofBool_append (msb : Bool) (lsbs : BitVec w) :
+    ofBool msb ++ lsbs = (cons msb lsbs).cast (Nat.add_comm ..) :=
+  rfl
+
+end bitwise
+
+section normalization_eqs
+/-! We add simp-lemmas that rewrite bitvector operations into the equivalent notation -/
+@[simp] theorem append_eq (x : BitVec w) (y : BitVec v)   : BitVec.append x y = x ++ y        := rfl
+@[simp] theorem shiftLeft_eq (x : BitVec w) (n : Nat)     : BitVec.shiftLeft x n = x <<< n    := rfl
+@[simp] theorem ushiftRight_eq (x : BitVec w) (n : Nat)   : BitVec.ushiftRight x n = x >>> n  := rfl
+@[simp] theorem not_eq (x : BitVec w)                     : BitVec.not x = ~~~x               := rfl
+@[simp] theorem and_eq (x y : BitVec w)                   : BitVec.and x y = x &&& y          := rfl
+@[simp] theorem or_eq (x y : BitVec w)                    : BitVec.or x y = x ||| y           := rfl
+@[simp] theorem xor_eq (x y : BitVec w)                   : BitVec.xor x y = x ^^^ y          := rfl
+@[simp] theorem neg_eq (x : BitVec w)                     : BitVec.neg x = -x                 := rfl
+@[simp] theorem add_eq (x y : BitVec w)                   : BitVec.add x y = x + y            := rfl
+@[simp] theorem sub_eq (x y : BitVec w)                   : BitVec.sub x y = x - y            := rfl
+@[simp] theorem mul_eq (x y : BitVec w)                   : BitVec.mul x y = x * y            := rfl
+@[simp] theorem zero_eq                                   : BitVec.zero n = 0#n               := rfl
+end normalization_eqs
+
+/-- Converts a list of `Bool`s to a big-endian `BitVec`. -/
+def ofBoolListBE : (bs : List Bool) → BitVec bs.length
+| [] => 0#0
+| b :: bs => cons b (ofBoolListBE bs)
+
+/-- Converts a list of `Bool`s to a little-endian `BitVec`. -/
+def ofBoolListLE : (bs : List Bool) → BitVec bs.length
+| [] => 0#0
+| b :: bs => concat (ofBoolListLE bs) b
+
+end BitVec

src/Init/Data/BitVec/Bitblast.lean

@@ -0,0 +1,162 @@
+/-
+Copyright (c) 2024 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Harun Khan, Abdalrhman M Mohamed, Joe Hendrix
+-/
+prelude
+import Init.Data.BitVec.Folds
+import Init.Data.Nat.Mod
+
+/-!
+# Bitblasting of bitvectors
+
+This module provides theorems for showing the equivalence between BitVec operations using
+the `Fin 2^n` representation and Boolean vectors.  It is still under development, but
+intended to provide a path for converting SAT and SMT solver proofs about BitVectors
+as vectors of bits into proofs about Lean `BitVec` values.
+
+The module is named for the bit-blasting operation in an SMT solver that converts bitvector
+expressions into expressions about individual bits in each vector.
+
+## Main results
+* `x + y : BitVec w` is `(adc x y false).2`.
+
+
+## Future work
+All other operations are to be PR'ed later and are already proved in
+https://github.com/mhk119/lean-smt/blob/bitvec/Smt/Data/Bitwise.lean.
+
+-/
+
+open Nat Bool
+
+namespace Bool
+
+/-- At least two out of three booleans are true. -/
+abbrev atLeastTwo (a b c : Bool) : Bool := a && b || a && c || b && c
+
+@[simp] theorem atLeastTwo_false_left  : atLeastTwo false b c = (b && c) := by simp [atLeastTwo]
+@[simp] theorem atLeastTwo_false_mid   : atLeastTwo a false c = (a && c) := by simp [atLeastTwo]
+@[simp] theorem atLeastTwo_false_right : atLeastTwo a b false = (a && b) := by simp [atLeastTwo]
+@[simp] theorem atLeastTwo_true_left   : atLeastTwo true b c  = (b || c) := by cases b <;> cases c <;> simp [atLeastTwo]
+@[simp] theorem atLeastTwo_true_mid    : atLeastTwo a true c  = (a || c) := by cases a <;> cases c <;> simp [atLeastTwo]
+@[simp] theorem atLeastTwo_true_right  : atLeastTwo a b true  = (a || b) := by cases a <;> cases b <;> simp [atLeastTwo]
+
+end Bool
+
+/-! ### Preliminaries -/
+
+namespace BitVec
+
+private theorem testBit_limit {x i : Nat} (x_lt_succ : x < 2^(i+1)) :
+    testBit x i = decide (x ≥ 2^i) := by
+  cases xi : testBit x i with
+  | true =>
+    simp [testBit_implies_ge xi]
+  | false =>
+    simp
+    cases Nat.lt_or_ge x (2^i) with
+    | inl x_lt =>
+      exact x_lt
+    | inr x_ge =>
+      have ⟨j, ⟨j_ge, jp⟩⟩  := ge_two_pow_implies_high_bit_true x_ge
+      cases Nat.lt_or_eq_of_le j_ge with
+      | inr x_eq =>
+        simp [x_eq, jp] at xi
+      | inl x_lt =>
+        exfalso
+        apply Nat.lt_irrefl
+        calc x < 2^(i+1) := x_lt_succ
+             _ ≤ 2 ^ j := Nat.pow_le_pow_of_le_right Nat.zero_lt_two x_lt
+             _ ≤ x := testBit_implies_ge jp
+
+private theorem mod_two_pow_succ (x i : Nat) :
+    x % 2^(i+1) = 2^i*(x.testBit i).toNat + x % (2 ^ i):= by
+  rw [Nat.mod_pow_succ, Nat.add_comm, Nat.toNat_testBit]
+
+private theorem mod_two_pow_add_mod_two_pow_add_bool_lt_two_pow_succ
+     (x y i : Nat) (c : Bool) : x % 2^i + (y % 2^i + c.toNat) < 2^(i+1) := by
+  have : c.toNat ≤ 1 := Bool.toNat_le c
+  rw [Nat.pow_succ]
+  omega
+
+/-! ### Addition -/
+
+/-- carry i x y c returns true if the `i` carry bit is true when computing `x + y + c`. -/
+def carry (i : Nat) (x y : BitVec w) (c : Bool) : Bool :=
+  decide (x.toNat % 2^i + y.toNat % 2^i + c.toNat ≥ 2^i)
+
+@[simp] theorem carry_zero : carry 0 x y c = c := by
+  cases c <;> simp [carry, mod_one]
+
+theorem carry_succ (i : Nat) (x y : BitVec w) (c : Bool) :
+    carry (i+1) x y c = atLeastTwo (x.getLsb i) (y.getLsb i) (carry i x y c) := by
+  simp only [carry, mod_two_pow_succ, atLeastTwo, getLsb]
+  simp only [Nat.pow_succ']
+  have sum_bnd : x.toNat%2^i + (y.toNat%2^i + c.toNat) < 2*2^i := by
+    simp only [← Nat.pow_succ']
+    exact mod_two_pow_add_mod_two_pow_add_bool_lt_two_pow_succ ..
+  cases x.toNat.testBit i <;> cases y.toNat.testBit i <;> (simp; omega)
+
+/-- Carry function for bitwise addition. -/
+def adcb (x y c : Bool) : Bool × Bool := (atLeastTwo x y c, Bool.xor x (Bool.xor y c))
+
+/-- Bitwise addition implemented via a ripple carry adder. -/
+def adc (x y : BitVec w) : Bool → Bool × BitVec w :=
+  iunfoldr fun (i : Fin w) c => adcb (x.getLsb i) (y.getLsb i) c
+
+theorem getLsb_add_add_bool {i : Nat} (i_lt : i < w) (x y : BitVec w) (c : Bool) :
+    getLsb (x + y + zeroExtend w (ofBool c)) i =
+      Bool.xor (getLsb x i) (Bool.xor (getLsb y i) (carry i x y c)) := by
+  let ⟨x, x_lt⟩ := x
+  let ⟨y, y_lt⟩ := y
+  simp only [getLsb, toNat_add, toNat_zeroExtend, i_lt, toNat_ofFin, toNat_ofBool,
+    Nat.mod_add_mod, Nat.add_mod_mod]
+  apply Eq.trans
+  rw [← Nat.div_add_mod x (2^i), ← Nat.div_add_mod y (2^i)]
+  simp only
+    [ Nat.testBit_mod_two_pow,
+      Nat.testBit_mul_two_pow_add_eq,
+      i_lt,
+      decide_True,
+      Bool.true_and,
+      Nat.add_assoc,
+      Nat.add_left_comm (_%_) (_ * _) _,
+      testBit_limit (mod_two_pow_add_mod_two_pow_add_bool_lt_two_pow_succ x y i c)
+    ]
+  simp [testBit_to_div_mod, carry, Nat.add_assoc]
+
+theorem getLsb_add {i : Nat} (i_lt : i < w) (x y : BitVec w) :
+    getLsb (x + y) i =
+      Bool.xor (getLsb x i) (Bool.xor (getLsb y i) (carry i x y false)) := by
+  simpa using getLsb_add_add_bool i_lt x y false
+
+theorem adc_spec (x y : BitVec w) (c : Bool) :
+    adc x y c = (carry w x y c, x + y + zeroExtend w (ofBool c)) := by
+  simp only [adc]
+  apply iunfoldr_replace
+          (fun i => carry i x y c)
+          (x + y + zeroExtend w (ofBool c))
+          c
+  case init =>
+    simp [carry, Nat.mod_one]
+    cases c <;> rfl
+  case step =>
+    simp [adcb, Prod.mk.injEq, carry_succ, getLsb_add_add_bool]
+
+theorem add_eq_adc (w : Nat) (x y : BitVec w) : x + y = (adc x y false).snd := by
+  simp [adc_spec]
+
+/-! ### add -/
+
+/-- Adding a bitvector to its own complement yields the all ones bitpattern -/
+@[simp] theorem add_not_self (x : BitVec w) : x + ~~~x = allOnes w := by
+  rw [add_eq_adc, adc, iunfoldr_replace (fun _ => false) (allOnes w)]
+  · rfl
+  · simp [adcb, atLeastTwo]
+
+/-- Subtracting `x` from the all ones bitvector is equivalent to taking its complement -/
+theorem allOnes_sub_eq_not (x : BitVec w) : allOnes w - x = ~~~x := by
+  rw [← add_not_self x, BitVec.add_comm, add_sub_cancel]
+
+end BitVec

src/Init/Data/BitVec/Folds.lean

@@ -0,0 +1,61 @@
+/-
+Copyright (c) 2023 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Joe Hendrix
+-/
+prelude
+import Init.Data.BitVec.Lemmas
+import Init.Data.Nat.Lemmas
+import Init.Data.Fin.Iterate
+
+namespace BitVec
+
+/--
+iunfoldr is an iterative operation that applies a function `f` repeatedly.
+
+It produces a sequence of state values `[s_0, s_1 .. s_w]` and a bitvector
+`v` where `f i s_i = (s_{i+1}, b_i)` and `b_i` is bit `i`th least-significant bit
+in `v` (e.g., `getLsb v i = b_i`).
+
+Theorems involving `iunfoldr` can be eliminated using `iunfoldr_replace` below.
+-/
+def iunfoldr (f : Fin w -> α → α × Bool) (s : α) : α × BitVec w :=
+  Fin.hIterate (fun i => α × BitVec i) (s, nil) fun i q =>
+    (fun p => ⟨p.fst, cons p.snd q.snd⟩) (f i q.fst)
+
+theorem iunfoldr.fst_eq
+    {f : Fin w → α → α × Bool} (state : Nat → α) (s : α)
+    (init : s = state 0)
+    (ind : ∀(i : Fin w), (f i (state i.val)).fst = state (i.val+1)) :
+    (iunfoldr f s).fst = state w := by
+  unfold iunfoldr
+  apply Fin.hIterate_elim (fun i (p : α × BitVec i) => p.fst = state i)
+  case init =>
+    exact init
+  case step =>
+    intro i ⟨s, v⟩ p
+    simp_all [ind i]
+
+private theorem iunfoldr.eq_test
+    {f : Fin w → α → α × Bool} (state : Nat → α) (value : BitVec w) (a : α)
+    (init : state 0 = a)
+    (step : ∀(i : Fin w), f i (state i.val) = (state (i.val+1), value.getLsb i.val)) :
+    iunfoldr f a = (state w, BitVec.truncate w value) := by
+  apply Fin.hIterate_eq (fun i => ((state i, BitVec.truncate i value) : α × BitVec i))
+  case init =>
+    simp only [init, eq_nil]
+  case step =>
+    intro i
+    simp_all [truncate_succ]
+
+/--
+Correctness theorem for `iunfoldr`.
+-/
+theorem iunfoldr_replace
+    {f : Fin w → α → α × Bool} (state : Nat → α) (value : BitVec w) (a : α)
+    (init : state 0 = a)
+    (step : ∀(i : Fin w), f i (state i.val) = (state (i.val+1), value.getLsb i.val)) :
+    iunfoldr f a = (state w, value) := by
+  simp [iunfoldr.eq_test state value a init step]
+
+end BitVec

src/Init/Data/BitVec/Lemmas.lean

@@ -0,0 +1,995 @@
+/-
+Copyright (c) 2023 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Joe Hendrix, Harun Khan, Alex Keizer, Abdalrhman M Mohamed,
+-/
+prelude
+import Init.Data.Bool
+import Init.Data.BitVec.Basic
+import Init.Data.Fin.Lemmas
+import Init.Data.Nat.Lemmas
+
+namespace BitVec
+
+/--
+This normalized a bitvec using `ofFin` to `ofNat`.
+-/
+theorem ofFin_eq_ofNat : @BitVec.ofFin w (Fin.mk x lt) = BitVec.ofNat w x := by
+  simp only [BitVec.ofNat, Fin.ofNat', lt, Nat.mod_eq_of_lt]
+
+/-- Prove equality of bitvectors in terms of nat operations. -/
+theorem eq_of_toNat_eq {n} : ∀ {i j : BitVec n}, i.toNat = j.toNat → i = j
+  | ⟨_, _⟩, ⟨_, _⟩, rfl => rfl
+
+@[simp] theorem val_toFin (x : BitVec w) : x.toFin.val = x.toNat := rfl
+
+@[bv_toNat] theorem toNat_eq (x y : BitVec n) : x = y ↔ x.toNat = y.toNat :=
+  Iff.intro (congrArg BitVec.toNat) eq_of_toNat_eq
+
+@[bv_toNat] theorem toNat_ne (x y : BitVec n) : x ≠ y ↔ x.toNat ≠ y.toNat := by
+  rw [Ne, toNat_eq]
+
+theorem testBit_toNat (x : BitVec w) : x.toNat.testBit i = x.getLsb i := rfl
+
+@[simp] theorem getLsb_ofFin (x : Fin (2^n)) (i : Nat) :
+  getLsb (BitVec.ofFin x) i = x.val.testBit i := rfl
+
+@[simp] theorem getLsb_ge (x : BitVec w) (i : Nat) (ge : w ≤ i) : getLsb x i = false := by
+  let ⟨x, x_lt⟩ := x
+  simp
+  apply Nat.testBit_lt_two_pow
+  have p : 2^w ≤ 2^i := Nat.pow_le_pow_of_le_right (by omega) ge
+  omega
+
+@[simp] theorem getMsb_ge (x : BitVec w) (i : Nat) (ge : w ≤ i) : getMsb x i = false := by
+  rw [getMsb]
+  simp only [Bool.and_eq_false_imp, decide_eq_true_eq]
+  omega
+
+theorem lt_of_getLsb (x : BitVec w) (i : Nat) : getLsb x i = true → i < w := by
+  if h : i < w then
+    simp [h]
+  else
+    simp [Nat.ge_of_not_lt h]
+
+theorem lt_of_getMsb (x : BitVec w) (i : Nat) : getMsb x i = true → i < w := by
+  if h : i < w then
+    simp [h]
+  else
+    simp [Nat.ge_of_not_lt h]
+
+theorem getMsb_eq_getLsb (x : BitVec w) (i : Nat) : x.getMsb i = (decide (i < w) && x.getLsb (w - 1 - i)) := by
+  rw [getMsb]
+
+theorem getLsb_eq_getMsb (x : BitVec w) (i : Nat) : x.getLsb i = (decide (i < w) && x.getMsb (w - 1 - i)) := by
+  rw [getMsb]
+  by_cases h₁ : i < w <;> by_cases h₂ : w - 1 - i < w <;>
+    simp only [h₁, h₂] <;> simp only [decide_True, decide_False, Bool.false_and, Bool.and_false, Bool.true_and, Bool.and_true]
+  · congr
+    omega
+  all_goals
+    apply getLsb_ge
+    omega
+
+-- We choose `eq_of_getLsb_eq` as the `@[ext]` theorem for `BitVec`
+-- somewhat arbitrarily over `eq_of_getMsg_eq`.
+@[ext] theorem eq_of_getLsb_eq {x y : BitVec w}
+    (pred : ∀(i : Fin w), x.getLsb i.val = y.getLsb i.val) : x = y := by
+  apply eq_of_toNat_eq
+  apply Nat.eq_of_testBit_eq
+  intro i
+  if i_lt : i < w then
+    exact pred ⟨i, i_lt⟩
+  else
+    have p : i ≥ w := Nat.le_of_not_gt i_lt
+    simp [testBit_toNat, getLsb_ge _ _ p]
+
+theorem eq_of_getMsb_eq {x y : BitVec w}
+    (pred : ∀(i : Fin w), x.getMsb i = y.getMsb i.val) : x = y := by
+  simp only [getMsb] at pred
+  apply eq_of_getLsb_eq
+  intro ⟨i, i_lt⟩
+  if w_zero : w = 0 then
+    simp [w_zero]
+  else
+    have w_pos := Nat.pos_of_ne_zero w_zero
+    have r : i ≤ w - 1 := by
+      simp [Nat.le_sub_iff_add_le w_pos]
+      exact i_lt
+    have q_lt : w - 1 - i < w := by
+      simp only [Nat.sub_sub]
+      apply Nat.sub_lt w_pos
+      simp [Nat.succ_add]
+    have q := pred ⟨w - 1 - i, q_lt⟩
+    simpa [q_lt, Nat.sub_sub_self, r] using q
+
+@[simp] theorem of_length_zero {x : BitVec 0} : x = 0#0 := by ext; simp
+
+theorem eq_of_toFin_eq : ∀ {x y : BitVec w}, x.toFin = y.toFin → x = y
+  | ⟨_, _⟩, ⟨_, _⟩, rfl => rfl
+
+@[simp] theorem toNat_ofBool (b : Bool) : (ofBool b).toNat = b.toNat := by
+  cases b <;> rfl
+
+@[simp] theorem msb_ofBool (b : Bool) : (ofBool b).msb = b := by
+  cases b <;> simp [BitVec.msb]
+
+theorem ofNat_one (n : Nat) : BitVec.ofNat 1 n = BitVec.ofBool (n % 2 = 1) :=  by
+  rcases (Nat.mod_two_eq_zero_or_one n) with h | h <;> simp [h, BitVec.ofNat, Fin.ofNat']
+
+theorem ofBool_eq_iff_eq : ∀(b b' : Bool), BitVec.ofBool b = BitVec.ofBool b' ↔ b = b' := by
+  decide
+
+@[simp] theorem not_ofBool : ~~~ (ofBool b) = ofBool (!b) := by cases b <;> rfl
+
+@[simp, bv_toNat] theorem toNat_ofFin (x : Fin (2^n)) : (BitVec.ofFin x).toNat = x.val := rfl
+
+@[simp] theorem toNat_ofNatLt (x : Nat) (p : x < 2^w) : (x#'p).toNat = x := rfl
+
+@[simp] theorem getLsb_ofNatLt {n : Nat} (x : Nat) (lt : x < 2^n) (i : Nat) :
+  getLsb (x#'lt) i = x.testBit i := by
+  simp [getLsb, BitVec.ofNatLt]
+
+@[simp, bv_toNat] theorem toNat_ofNat (x w : Nat) : (x#w).toNat = x % 2^w := by
+  simp [BitVec.toNat, BitVec.ofNat, Fin.ofNat']
+
+-- Remark: we don't use `[simp]` here because simproc` subsumes it for literals.
+-- If `x` and `n` are not literals, applying this theorem eagerly may not be a good idea.
+theorem getLsb_ofNat (n : Nat) (x : Nat) (i : Nat) :
+  getLsb (x#n) i = (i < n && x.testBit i) := by
+  simp [getLsb, BitVec.ofNat, Fin.val_ofNat']
+
+@[simp, deprecated toNat_ofNat] theorem toNat_zero (n : Nat) : (0#n).toNat = 0 := by trivial
+
+@[simp] theorem getLsb_zero : (0#w).getLsb i = false := by simp [getLsb]
+
+@[simp] theorem getMsb_zero : (0#w).getMsb i = false := by simp [getMsb]
+
+@[simp] theorem toNat_mod_cancel (x : BitVec n) : x.toNat % (2^n) = x.toNat :=
+  Nat.mod_eq_of_lt x.isLt
+
+private theorem lt_two_pow_of_le {x m n : Nat} (lt : x < 2 ^ m) (le : m ≤ n) : x < 2 ^ n :=
+  Nat.lt_of_lt_of_le lt (Nat.pow_le_pow_of_le_right (by trivial : 0 < 2) le)
+
+/-! ### msb -/
+
+@[simp] theorem msb_zero : (0#w).msb = false := by simp [BitVec.msb, getMsb]
+
+theorem msb_eq_getLsb_last (x : BitVec w) :
+    x.msb = x.getLsb (w - 1) := by
+  simp [BitVec.msb, getMsb, getLsb]
+  rcases w  with rfl | w
+  · simp [BitVec.eq_nil x]
+  · simp
+
+@[bv_toNat] theorem getLsb_last (x : BitVec w) :
+    x.getLsb (w-1) = decide (2 ^ (w-1) ≤ x.toNat) := by
+  rcases w with rfl | w
+  · simp
+  · simp only [Nat.zero_lt_succ, decide_True, getLsb, Nat.testBit, Nat.succ_sub_succ_eq_sub,
+    Nat.sub_zero, Nat.and_one_is_mod, Bool.true_and, Nat.shiftRight_eq_div_pow]
+    rcases (Nat.lt_or_ge (BitVec.toNat x) (2 ^ w)) with h | h
+    · simp [Nat.div_eq_of_lt h, h]
+    · simp only [h]
+      rw [Nat.div_eq_sub_div (Nat.two_pow_pos w) h, Nat.div_eq_of_lt]
+      · decide
+      · have : BitVec.toNat x < 2^w + 2^w := by simpa [Nat.pow_succ, Nat.mul_two] using x.isLt
+        omega
+
+@[bv_toNat] theorem getLsb_succ_last (x : BitVec (w + 1)) :
+    x.getLsb w = decide (2 ^ w ≤ x.toNat) := getLsb_last x
+
+@[bv_toNat] theorem msb_eq_decide (x : BitVec w) : BitVec.msb x = decide (2 ^ (w-1) ≤ x.toNat) := by
+  simp [msb_eq_getLsb_last, getLsb_last]
+
+theorem toNat_ge_of_msb_true {x : BitVec n} (p : BitVec.msb x = true) : x.toNat ≥ 2^(n-1) := by
+  match n with
+  | 0 =>
+    simp [BitVec.msb, BitVec.getMsb] at p
+  | n + 1 =>
+    simp [BitVec.msb_eq_decide] at p
+    simp only [Nat.add_sub_cancel]
+    exact p
+
+/-! ### cast -/
+
+@[simp, bv_toNat] theorem toNat_cast (h : w = v) (x : BitVec w) : (cast h x).toNat = x.toNat := rfl
+@[simp] theorem toFin_cast (h : w = v) (x : BitVec w) :
+    (cast h x).toFin = x.toFin.cast (by rw [h]) :=
+  rfl
+
+@[simp] theorem getLsb_cast (h : w = v) (x : BitVec w) : (cast h x).getLsb i = x.getLsb i := by
+  subst h; simp
+
+@[simp] theorem getMsb_cast (h : w = v) (x : BitVec w) : (cast h x).getMsb i = x.getMsb i := by
+  subst h; simp
+@[simp] theorem msb_cast (h : w = v) (x : BitVec w) : (cast h x).msb = x.msb := by
+  simp [BitVec.msb]
+
+/-! ### toInt/ofInt -/
+
+/-- Prove equality of bitvectors in terms of nat operations. -/
+theorem toInt_eq_toNat_cond (i : BitVec n) :
+    i.toInt =
+      if 2*i.toNat < 2^n then
+        (i.toNat : Int)
+      else
+        (i.toNat : Int) - (2^n : Nat) := by
+  unfold BitVec.toInt
+  split <;> omega
+
+theorem toInt_eq_toNat_bmod (x : BitVec n) : x.toInt = Int.bmod x.toNat (2^n) := by
+  simp only [toInt_eq_toNat_cond]
+  split
+  case inl g =>
+    rw [Int.bmod_pos] <;> simp only [←Int.ofNat_emod, toNat_mod_cancel]
+    omega
+  case inr g =>
+    rw [Int.bmod_neg] <;> simp only [←Int.ofNat_emod, toNat_mod_cancel]
+    omega
+
+/-- Prove equality of bitvectors in terms of nat operations. -/
+theorem eq_of_toInt_eq {i j : BitVec n} : i.toInt = j.toInt → i = j := by
+  intro eq
+  simp [toInt_eq_toNat_cond] at eq
+  apply eq_of_toNat_eq
+  revert eq
+  have _ilt := i.isLt
+  have _jlt := j.isLt
+  split <;> split <;> omega
+
+@[simp] theorem toNat_ofInt {n : Nat} (i : Int) :
+  (BitVec.ofInt n i).toNat = (i % (2^n : Nat)).toNat := by
+  unfold BitVec.ofInt
+  simp
+
+theorem toInt_ofNat {n : Nat} (x : Nat) :
+  (BitVec.ofNat n x).toInt = (x : Int).bmod (2^n) := by
+  simp [toInt_eq_toNat_bmod]
+
+@[simp] theorem toInt_ofInt {n : Nat} (i : Int) :
+  (BitVec.ofInt n i).toInt = i.bmod (2^n) := by
+  have _ := Nat.two_pow_pos n
+  have p : 0 ≤ i % (2^n : Nat) := by omega
+  simp [toInt_eq_toNat_bmod, Int.toNat_of_nonneg p]
+
+/-! ### zeroExtend and truncate -/
+
+@[simp, bv_toNat] theorem toNat_zeroExtend' {m n : Nat} (p : m ≤ n) (x : BitVec m) :
+    (zeroExtend' p x).toNat = x.toNat := by
+  unfold zeroExtend'
+  simp [p, x.isLt, Nat.mod_eq_of_lt]
+
+@[bv_toNat] theorem toNat_zeroExtend (i : Nat) (x : BitVec n) :
+    BitVec.toNat (zeroExtend i x) = x.toNat % 2^i := by
+  let ⟨x, lt_n⟩ := x
+  simp only [zeroExtend]
+  if n_le_i : n ≤ i then
+    have x_lt_two_i : x < 2 ^ i := lt_two_pow_of_le lt_n n_le_i
+    simp [n_le_i, Nat.mod_eq_of_lt, x_lt_two_i]
+  else
+    simp [n_le_i, toNat_ofNat]
+
+theorem zeroExtend'_eq {x : BitVec w} (h : w ≤ v) : x.zeroExtend' h = x.zeroExtend v := by
+  apply eq_of_toNat_eq
+  rw [toNat_zeroExtend, toNat_zeroExtend']
+  rw [Nat.mod_eq_of_lt]
+  exact Nat.lt_of_lt_of_le x.isLt (Nat.pow_le_pow_right (Nat.zero_lt_two) h)
+
+@[simp, bv_toNat] theorem toNat_truncate (x : BitVec n) : (truncate i x).toNat = x.toNat % 2^i :=
+  toNat_zeroExtend i x
+
+@[simp] theorem zeroExtend_eq (x : BitVec n) : zeroExtend n x = x := by
+  apply eq_of_toNat_eq
+  let ⟨x, lt_n⟩ := x
+  simp [truncate, zeroExtend]
+
+@[simp] theorem zeroExtend_zero (m n : Nat) : zeroExtend m (0#n) = 0#m := by
+  apply eq_of_toNat_eq
+  simp [toNat_zeroExtend]
+
+@[simp] theorem truncate_eq (x : BitVec n) : truncate n x = x := zeroExtend_eq x
+
+@[simp] theorem ofNat_toNat (m : Nat) (x : BitVec n) : x.toNat#m = truncate m x := by
+  apply eq_of_toNat_eq
+  simp
+
+/-- Moves one-sided left toNat equality to BitVec equality. -/
+theorem toNat_eq_nat (x : BitVec w) (y : Nat)
+  : (x.toNat = y) ↔ (y < 2^w ∧ (x = y#w)) := by
+  apply Iff.intro
+  · intro eq
+    simp at eq
+    have lt := x.isLt
+    simp [eq] at lt
+    simp [←eq, lt, x.isLt]
+  · intro eq
+    simp [Nat.mod_eq_of_lt, eq]
+
+/-- Moves one-sided right toNat equality to BitVec equality. -/
+theorem nat_eq_toNat (x : BitVec w) (y : Nat)
+  : (y = x.toNat) ↔ (y < 2^w ∧ (x = y#w)) := by
+  rw [@eq_comm _ _ x.toNat]
+  apply toNat_eq_nat
+
+@[simp] theorem getLsb_zeroExtend' (ge : m ≥ n) (x : BitVec n) (i : Nat) :
+    getLsb (zeroExtend' ge x) i = getLsb x i := by
+  simp [getLsb, toNat_zeroExtend']
+
+@[simp] theorem getMsb_zeroExtend' (ge : m ≥ n) (x : BitVec n) (i : Nat) :
+    getMsb (zeroExtend' ge x) i = (decide (i ≥ m - n) && getMsb x (i - (m - n))) := by
+  simp only [getMsb, getLsb_zeroExtend', gt_iff_lt]
+  by_cases h₁ : decide (i < m) <;> by_cases h₂ : decide (i ≥ m - n) <;> by_cases h₃ : decide (i - (m - n) < n) <;>
+    by_cases h₄ : n - 1 - (i - (m - n)) = m - 1 - i
+  all_goals
+    simp only [h₁, h₂, h₃, h₄]
+    simp_all only [ge_iff_le, decide_eq_true_eq, Nat.not_le, Nat.not_lt, Bool.true_and,
+      Bool.false_and, Bool.and_self] <;>
+    (try apply getLsb_ge) <;>
+    (try apply (getLsb_ge _ _ _).symm) <;>
+    omega
+
+@[simp] theorem getLsb_zeroExtend (m : Nat) (x : BitVec n) (i : Nat) :
+    getLsb (zeroExtend m x) i = (decide (i < m) && getLsb x i) := by
+  simp [getLsb, toNat_zeroExtend, Nat.testBit_mod_two_pow]
+
+@[simp] theorem getMsb_zeroExtend_add {x : BitVec w} (h : k ≤ i) :
+    (x.zeroExtend (w + k)).getMsb i = x.getMsb (i - k) := by
+  by_cases h : w = 0
+  · subst h; simp
+  simp only [getMsb, getLsb_zeroExtend]
+  by_cases h₁ : i < w + k <;> by_cases h₂ : i - k < w <;> by_cases h₃ : w + k - 1 - i < w + k
+    <;> simp [h₁, h₂, h₃]
+  · congr 1
+    omega
+  all_goals (first | apply getLsb_ge | apply Eq.symm; apply getLsb_ge)
+    <;> omega
+
+@[simp] theorem getLsb_truncate (m : Nat) (x : BitVec n) (i : Nat) :
+    getLsb (truncate m x) i = (decide (i < m) && getLsb x i) :=
+  getLsb_zeroExtend m x i
+
+theorem msb_truncate (x : BitVec w) : (x.truncate (k + 1)).msb = x.getLsb k := by
+  simp [BitVec.msb, getMsb]
+
+@[simp] theorem zeroExtend_zeroExtend_of_le (x : BitVec w) (h : k ≤ l) :
+    (x.zeroExtend l).zeroExtend k = x.zeroExtend k := by
+  ext i
+  simp only [getLsb_zeroExtend, Fin.is_lt, decide_True, Bool.true_and]
+  have p := lt_of_getLsb x i
+  revert p
+  cases getLsb x i <;> simp; omega
+
+@[simp] theorem truncate_truncate_of_le (x : BitVec w) (h : k ≤ l) :
+    (x.truncate l).truncate k = x.truncate k :=
+  zeroExtend_zeroExtend_of_le x h
+
+@[simp] theorem truncate_cast {h : w = v} : (cast h x).truncate k = x.truncate k := by
+  apply eq_of_getLsb_eq
+  simp
+
+theorem msb_zeroExtend (x : BitVec w) : (x.zeroExtend v).msb = (decide (0 < v) && x.getLsb (v - 1)) := by
+  rw [msb_eq_getLsb_last]
+  simp only [getLsb_zeroExtend]
+  cases getLsb x (v - 1) <;> simp; omega
+
+theorem msb_zeroExtend' (x : BitVec w) (h : w ≤ v) : (x.zeroExtend' h).msb = (decide (0 < v) && x.getLsb (v - 1)) := by
+  rw [zeroExtend'_eq, msb_zeroExtend]
+
+/-! ## extractLsb -/
+
+@[simp]
+protected theorem extractLsb_ofFin {n} (x : Fin (2^n)) (hi lo : Nat) :
+  extractLsb hi lo (@BitVec.ofFin n x) = .ofNat (hi-lo+1) (x.val >>> lo) := rfl
+
+@[simp]
+protected theorem extractLsb_ofNat (x n : Nat) (hi lo : Nat) :
+  extractLsb hi lo x#n = .ofNat (hi - lo + 1) ((x % 2^n) >>> lo) := by
+  apply eq_of_getLsb_eq
+  intro ⟨i, _lt⟩
+  simp [BitVec.ofNat]
+
+@[simp] theorem extractLsb'_toNat (s m : Nat) (x : BitVec n) :
+  (extractLsb' s m x).toNat = (x.toNat >>> s) % 2^m := rfl
+
+@[simp] theorem extractLsb_toNat (hi lo : Nat) (x : BitVec n) :
+  (extractLsb hi lo x).toNat = (x.toNat >>> lo) % 2^(hi-lo+1) := rfl
+
+@[simp] theorem getLsb_extract (hi lo : Nat) (x : BitVec n) (i : Nat) :
+    getLsb (extractLsb hi lo x) i = (i ≤ (hi-lo) && getLsb x (lo+i)) := by
+  unfold getLsb
+  simp [Nat.lt_succ]
+
+/-! ### allOnes -/
+
+@[simp] theorem toNat_allOnes : (allOnes v).toNat = 2^v - 1 := by
+  unfold allOnes
+  simp
+
+@[simp] theorem getLsb_allOnes : (allOnes v).getLsb i = decide (i < v) := by
+  simp [allOnes]
+
+/-! ### or -/
+
+@[simp] theorem toNat_or (x y : BitVec v) :
+    BitVec.toNat (x ||| y) = BitVec.toNat x ||| BitVec.toNat y := rfl
+
+@[simp] theorem toFin_or (x y : BitVec v) :
+    BitVec.toFin (x ||| y) = BitVec.toFin x ||| BitVec.toFin y := by
+  apply Fin.eq_of_val_eq
+  exact (Nat.mod_eq_of_lt <| Nat.or_lt_two_pow x.isLt y.isLt).symm
+
+@[simp] theorem getLsb_or {x y : BitVec v} : (x ||| y).getLsb i = (x.getLsb i || y.getLsb i) := by
+  rw [← testBit_toNat, getLsb, getLsb]
+  simp
+
+@[simp] theorem getMsb_or {x y : BitVec w} : (x ||| y).getMsb i = (x.getMsb i || y.getMsb i) := by
+  simp only [getMsb]
+  by_cases h : i < w <;> simp [h]
+
+@[simp] theorem msb_or {x y : BitVec w} : (x ||| y).msb = (x.msb || y.msb) := by
+  simp [BitVec.msb]
+
+@[simp] theorem truncate_or {x y : BitVec w} :
+    (x ||| y).truncate k = x.truncate k ||| y.truncate k := by
+  ext
+  simp
+
+/-! ### and -/
+
+@[simp] theorem toNat_and (x y : BitVec v) :
+    BitVec.toNat (x &&& y) = BitVec.toNat x &&& BitVec.toNat y := rfl
+
+@[simp] theorem toFin_and (x y : BitVec v) :
+    BitVec.toFin (x &&& y) = BitVec.toFin x &&& BitVec.toFin y := by
+  apply Fin.eq_of_val_eq
+  exact (Nat.mod_eq_of_lt <| Nat.and_lt_two_pow _ y.isLt).symm
+
+@[simp] theorem getLsb_and {x y : BitVec v} : (x &&& y).getLsb i = (x.getLsb i && y.getLsb i) := by
+  rw [← testBit_toNat, getLsb, getLsb]
+  simp
+
+@[simp] theorem getMsb_and {x y : BitVec w} : (x &&& y).getMsb i = (x.getMsb i && y.getMsb i) := by
+  simp only [getMsb]
+  by_cases h : i < w <;> simp [h]
+
+@[simp] theorem msb_and {x y : BitVec w} : (x &&& y).msb = (x.msb && y.msb) := by
+  simp [BitVec.msb]
+
+@[simp] theorem truncate_and {x y : BitVec w} :
+    (x &&& y).truncate k = x.truncate k &&& y.truncate k := by
+  ext
+  simp
+
+/-! ### xor -/
+
+@[simp] theorem toNat_xor (x y : BitVec v) :
+    BitVec.toNat (x ^^^ y) = BitVec.toNat x ^^^ BitVec.toNat y := rfl
+
+@[simp] theorem toFin_xor (x y : BitVec v) :
+    BitVec.toFin (x ^^^ y) = BitVec.toFin x ^^^ BitVec.toFin y := by
+  apply Fin.eq_of_val_eq
+  exact (Nat.mod_eq_of_lt <| Nat.xor_lt_two_pow x.isLt y.isLt).symm
+
+@[simp] theorem getLsb_xor {x y : BitVec v} :
+    (x ^^^ y).getLsb i = (xor (x.getLsb i) (y.getLsb i)) := by
+  rw [← testBit_toNat, getLsb, getLsb]
+  simp
+
+@[simp] theorem truncate_xor {x y : BitVec w} :
+    (x ^^^ y).truncate k = x.truncate k ^^^ y.truncate k := by
+  ext
+  simp
+
+/-! ### not -/
+
+theorem not_def {x : BitVec v} : ~~~x = allOnes v ^^^ x := rfl
+
+@[simp, bv_toNat] theorem toNat_not {x : BitVec v} : (~~~x).toNat = 2^v - 1 - x.toNat := by
+  rw [Nat.sub_sub, Nat.add_comm, not_def, toNat_xor]
+  apply Nat.eq_of_testBit_eq
+  intro i
+  simp only [toNat_allOnes, Nat.testBit_xor, Nat.testBit_two_pow_sub_one]
+  match h : BitVec.toNat x with
+  | 0 => simp
+  | y+1 =>
+    rw [Nat.succ_eq_add_one] at h
+    rw [← h]
+    rw [Nat.testBit_two_pow_sub_succ (isLt _)]
+    · cases w : decide (i < v)
+      · simp at w
+        simp [w]
+        rw [Nat.testBit_lt_two_pow]
+        calc BitVec.toNat x < 2 ^ v := isLt _
+          _ ≤ 2 ^ i := Nat.pow_le_pow_of_le_right Nat.zero_lt_two w
+      · simp
+
+@[simp] theorem toFin_not (x : BitVec w) :
+    (~~~x).toFin = x.toFin.rev := by
+  apply Fin.val_inj.mp
+  simp only [val_toFin, toNat_not, Fin.val_rev]
+  omega
+
+@[simp] theorem getLsb_not {x : BitVec v} : (~~~x).getLsb i = (decide (i < v) && ! x.getLsb i) := by
+  by_cases h' : i < v <;> simp_all [not_def]
+
+@[simp] theorem truncate_not {x : BitVec w} (h : k ≤ w) :
+    (~~~x).truncate k = ~~~(x.truncate k) := by
+  ext
+  simp [h]
+  omega
+
+/-! ### cast -/
+
+@[simp] theorem not_cast {x : BitVec w} (h : w = w') : ~~~(cast h x) = cast h (~~~x) := by
+  ext
+  simp_all [lt_of_getLsb]
+
+@[simp] theorem and_cast {x y : BitVec w} (h : w = w') : cast h x &&& cast h y = cast h (x &&& y) := by
+  ext
+  simp_all [lt_of_getLsb]
+
+@[simp] theorem or_cast {x y : BitVec w} (h : w = w') : cast h x ||| cast h y = cast h (x ||| y) := by
+  ext
+  simp_all [lt_of_getLsb]
+
+@[simp] theorem xor_cast {x y : BitVec w} (h : w = w') : cast h x &&& cast h y = cast h (x &&& y) := by
+  ext
+  simp_all [lt_of_getLsb]
+
+/-! ### shiftLeft -/
+
+@[simp, bv_toNat] theorem toNat_shiftLeft {x : BitVec v} :
+    BitVec.toNat (x <<< n) = BitVec.toNat x <<< n % 2^v :=
+  BitVec.toNat_ofNat _ _
+
+@[simp] theorem toFin_shiftLeft {n : Nat} (x : BitVec w) :
+    BitVec.toFin (x <<< n) = Fin.ofNat' (x.toNat <<< n) (Nat.two_pow_pos w) := rfl
+
+@[simp] theorem getLsb_shiftLeft (x : BitVec m) (n) :
+    getLsb (x <<< n) i = (decide (i < m) && !decide (i < n) && getLsb x (i - n)) := by
+  rw [← testBit_toNat, getLsb]
+  simp only [toNat_shiftLeft, Nat.testBit_mod_two_pow, Nat.testBit_shiftLeft, ge_iff_le]
+  -- This step could be a case bashing tactic.
+  cases h₁ : decide (i < m) <;> cases h₂ : decide (n ≤ i) <;> cases h₃ : decide (i < n)
+  all_goals { simp_all <;> omega }
+
+@[simp] theorem getMsb_shiftLeft (x : BitVec w) (i) :
+    (x <<< i).getMsb k = x.getMsb (k + i) := by
+  simp only [getMsb, getLsb_shiftLeft]
+  by_cases h : w = 0
+  · subst h; simp
+  have t : w - 1 - k < w := by omega
+  simp only [t]
+  simp only [decide_True, Nat.sub_sub, Bool.true_and, Nat.add_assoc]
+  by_cases h₁ : k < w <;> by_cases h₂ : w - (1 + k) < i <;> by_cases h₃ : k + i < w
+    <;> simp [h₁, h₂, h₃]
+    <;> (first | apply getLsb_ge | apply Eq.symm; apply getLsb_ge)
+    <;> omega
+
+theorem shiftLeftZeroExtend_eq {x : BitVec w} :
+    shiftLeftZeroExtend x n = zeroExtend (w+n) x <<< n := by
+  apply eq_of_toNat_eq
+  rw [shiftLeftZeroExtend, zeroExtend]
+  split
+  · simp
+    rw [Nat.mod_eq_of_lt]
+    rw [Nat.shiftLeft_eq, Nat.pow_add]
+    exact Nat.mul_lt_mul_of_pos_right x.isLt (Nat.two_pow_pos _)
+  · omega
+
+@[simp] theorem getLsb_shiftLeftZeroExtend (x : BitVec m) (n : Nat) :
+    getLsb (shiftLeftZeroExtend x n) i = ((! decide (i < n)) && getLsb x (i - n)) := by
+  rw [shiftLeftZeroExtend_eq]
+  simp only [getLsb_shiftLeft, getLsb_zeroExtend]
+  cases h₁ : decide (i < n) <;> cases h₂ : decide (i - n < m + n) <;> cases h₃ : decide (i < m + n)
+    <;> simp_all
+    <;> (rw [getLsb_ge]; omega)
+
+@[simp] theorem getMsb_shiftLeftZeroExtend (x : BitVec m) (n : Nat) :
+    getMsb (shiftLeftZeroExtend x n) i = getMsb x i := by
+  have : n ≤ i + n := by omega
+  simp_all [shiftLeftZeroExtend_eq]
+
+@[simp] theorem msb_shiftLeftZeroExtend (x : BitVec w) (i : Nat) :
+    (shiftLeftZeroExtend x i).msb = x.msb := by
+  simp [shiftLeftZeroExtend_eq, BitVec.msb]
+
+/-! ### ushiftRight -/
+
+@[simp, bv_toNat] theorem toNat_ushiftRight (x : BitVec n) (i : Nat) :
+    (x >>> i).toNat = x.toNat >>> i := rfl
+
+@[simp] theorem getLsb_ushiftRight (x : BitVec n) (i j : Nat) :
+    getLsb (x >>> i) j = getLsb x (i+j) := by
+  unfold getLsb ; simp
+
+/-! ### append -/
+
+theorem append_def (x : BitVec v) (y : BitVec w) :
+    x ++ y = (shiftLeftZeroExtend x w ||| zeroExtend' (Nat.le_add_left w v) y) := rfl
+
+@[simp] theorem toNat_append (x : BitVec m) (y : BitVec n) :
+    (x ++ y).toNat = x.toNat <<< n ||| y.toNat :=
+  rfl
+
+@[simp] theorem getLsb_append {v : BitVec n} {w : BitVec m} :
+    getLsb (v ++ w) i = bif i < m then getLsb w i else getLsb v (i - m) := by
+  simp only [append_def, getLsb_or, getLsb_shiftLeftZeroExtend, getLsb_zeroExtend']
+  by_cases h : i < m
+  · simp [h]
+  · simp [h]; simp_all
+
+@[simp] theorem getMsb_append {v : BitVec n} {w : BitVec m} :
+    getMsb (v ++ w) i = bif n ≤ i then getMsb w (i - n) else getMsb v i := by
+  simp [append_def]
+  by_cases h : n ≤ i
+  · simp [h]
+  · simp [h]
+
+theorem msb_append {x : BitVec w} {y : BitVec v} :
+    (x ++ y).msb = bif (w == 0) then (y.msb) else (x.msb) := by
+  rw [← append_eq, append]
+  simp [msb_zeroExtend']
+  by_cases h : w = 0
+  · subst h
+    simp [BitVec.msb, getMsb]
+  · rw [cond_eq_if]
+    have q : 0 < w + v := by omega
+    have t : y.getLsb (w + v - 1) = false := getLsb_ge _ _ (by omega)
+    simp [h, q, t, BitVec.msb, getMsb]
+
+@[simp] theorem truncate_append {x : BitVec w} {y : BitVec v} :
+    (x ++ y).truncate k = if h : k ≤ v then y.truncate k else (x.truncate (k - v) ++ y).cast (by omega) := by
+  apply eq_of_getLsb_eq
+  intro i
+  simp only [getLsb_zeroExtend, Fin.is_lt, decide_True, getLsb_append, Bool.true_and]
+  split
+  · have t : i < v := by omega
+    simp [t]
+  · by_cases t : i < v
+    · simp [t]
+    · have t' : i - v < k - v := by omega
+      simp [t, t']
+
+@[simp] theorem truncate_cons {x : BitVec w} : (cons a x).truncate w = x := by
+  simp [cons]
+
+@[simp] theorem not_append {x : BitVec w} {y : BitVec v} : ~~~ (x ++ y) = (~~~ x) ++ (~~~ y) := by
+  ext i
+  simp only [getLsb_not, getLsb_append, cond_eq_if]
+  split
+  · simp_all
+  · simp_all; omega
+
+@[simp] theorem and_append {x₁ x₂ : BitVec w} {y₁ y₂ : BitVec v} :
+    (x₁ ++ y₁) &&& (x₂ ++ y₂) = (x₁ &&& x₂) ++ (y₁ &&& y₂) := by
+  ext i
+  simp only [getLsb_append, cond_eq_if]
+  split <;> simp [*]
+
+@[simp] theorem or_append {x₁ x₂ : BitVec w} {y₁ y₂ : BitVec v} :
+    (x₁ ++ y₁) ||| (x₂ ++ y₂) = (x₁ ||| x₂) ++ (y₁ ||| y₂) := by
+  ext i
+  simp only [getLsb_append, cond_eq_if]
+  split <;> simp [*]
+
+@[simp] theorem xor_append {x₁ x₂ : BitVec w} {y₁ y₂ : BitVec v} :
+    (x₁ ++ y₁) ^^^ (x₂ ++ y₂) = (x₁ ^^^ x₂) ++ (y₁ ^^^ y₂) := by
+  ext i
+  simp only [getLsb_append, cond_eq_if]
+  split <;> simp [*]
+
+/-! ### rev -/
+
+theorem getLsb_rev (x : BitVec w) (i : Fin w) :
+    x.getLsb i.rev = x.getMsb i := by
+  simp [getLsb, getMsb]
+  congr 1
+  omega
+
+theorem getMsb_rev (x : BitVec w) (i : Fin w) :
+    x.getMsb i.rev = x.getLsb i := by
+  simp only [← getLsb_rev]
+  simp only [Fin.rev]
+  congr
+  omega
+
+/-! ### cons -/
+
+@[simp] theorem toNat_cons (b : Bool) (x : BitVec w) :
+    (cons b x).toNat = (b.toNat <<< w) ||| x.toNat := by
+  let ⟨x, _⟩ := x
+  simp [cons, toNat_append, toNat_ofBool]
+
+/-- Variant of `toNat_cons` using `+` instead of `|||`. -/
+theorem toNat_cons' {x : BitVec w} :
+    (cons a x).toNat = (a.toNat <<< w) + x.toNat := by
+  simp [cons, Nat.shiftLeft_eq, Nat.mul_comm _ (2^w), Nat.mul_add_lt_is_or, x.isLt]
+
+@[simp] theorem getLsb_cons (b : Bool) {n} (x : BitVec n) (i : Nat) :
+    getLsb (cons b x) i = if i = n then b else getLsb x i := by
+  simp only [getLsb, toNat_cons, Nat.testBit_or]
+  rw [Nat.testBit_shiftLeft]
+  rcases Nat.lt_trichotomy i n with i_lt_n | i_eq_n | n_lt_i
+  · have p1 : ¬(n ≤ i) := by omega
+    have p2 : i ≠ n := by omega
+    simp [p1, p2]
+  · simp [i_eq_n, testBit_toNat]
+    cases b <;> trivial
+  · have p1 : i ≠ n := by omega
+    have p2 : i - n ≠ 0 := by omega
+    simp [p1, p2, Nat.testBit_bool_to_nat]
+
+@[simp] theorem msb_cons : (cons a x).msb = a := by
+  simp [cons, msb_cast, msb_append]
+
+@[simp] theorem getMsb_cons_zero : (cons a x).getMsb 0 = a := by
+  rw [← BitVec.msb, msb_cons]
+
+@[simp] theorem getMsb_cons_succ : (cons a x).getMsb (i + 1) = x.getMsb i := by
+  simp [cons, Nat.le_add_left 1 i]
+
+theorem truncate_succ (x : BitVec w) :
+    truncate (i+1) x = cons (getLsb x i) (truncate i x) := by
+  apply eq_of_getLsb_eq
+  intro j
+  simp only [getLsb_truncate, getLsb_cons, j.isLt, decide_True, Bool.true_and]
+  if j_eq : j.val = i then
+    simp [j_eq]
+  else
+    have j_lt : j.val < i := Nat.lt_of_le_of_ne (Nat.le_of_succ_le_succ j.isLt) j_eq
+    simp [j_eq, j_lt]
+
+theorem eq_msb_cons_truncate (x : BitVec (w+1)) : x = (cons x.msb (x.truncate w)) := by
+  ext i
+  simp
+  split <;> rename_i h
+  · simp [BitVec.msb, getMsb, h]
+  · by_cases h' : i < w
+    · simp_all
+    · omega
+
+@[simp] theorem not_cons (x : BitVec w) (b : Bool) : ~~~(cons b x) = cons (!b) (~~~x) := by
+  simp [cons]
+
+@[simp] theorem cons_or_cons (x y : BitVec w) (a b : Bool) :
+    (cons a x) ||| (cons b y) = cons (a || b) (x ||| y) := by
+  ext i; cases i using Fin.succRecOn <;> simp <;> split <;> rfl
+
+@[simp] theorem cons_and_cons (x y : BitVec w) (a b : Bool) :
+    (cons a x) &&& (cons b y) = cons (a && b) (x &&& y) := by
+  ext i; cases i using Fin.succRecOn <;> simp <;> split <;> rfl
+
+@[simp] theorem cons_xor_cons (x y : BitVec w) (a b : Bool) :
+    (cons a x) ^^^ (cons b y) = cons (xor a b) (x ^^^ y) := by
+  ext i; cases i using Fin.succRecOn <;> simp <;> split <;> rfl
+
+/-! ### concat -/
+
+@[simp] theorem toNat_concat (x : BitVec w) (b : Bool) :
+    (concat x b).toNat = x.toNat * 2 + b.toNat := by
+  apply Nat.eq_of_testBit_eq
+  simp only [concat, toNat_append, Nat.shiftLeft_eq, Nat.pow_one, toNat_ofBool, Nat.testBit_or]
+  cases b
+  · simp
+  · rintro (_ | i)
+    <;> simp [Nat.add_mod, Nat.add_comm, Nat.add_mul_div_right]
+
+theorem getLsb_concat (x : BitVec w) (b : Bool) (i : Nat) :
+    (concat x b).getLsb i = if i = 0 then b else x.getLsb (i - 1) := by
+  simp only [concat, getLsb, toNat_append, toNat_ofBool, Nat.testBit_or, Nat.shiftLeft_eq]
+  cases i
+  · simp [Nat.mod_eq_of_lt b.toNat_lt]
+  · simp [Nat.div_eq_of_lt b.toNat_lt]
+
+@[simp] theorem getLsb_concat_zero : (concat x b).getLsb 0 = b := by
+  simp [getLsb_concat]
+
+@[simp] theorem getLsb_concat_succ : (concat x b).getLsb (i + 1) = x.getLsb i := by
+  simp [getLsb_concat]
+
+@[simp] theorem not_concat (x : BitVec w) (b : Bool) : ~~~(concat x b) = concat (~~~x) !b := by
+  ext i; cases i using Fin.succRecOn <;> simp [*, Nat.succ_lt_succ]
+
+@[simp] theorem concat_or_concat (x y : BitVec w) (a b : Bool) :
+    (concat x a) ||| (concat y b) = concat (x ||| y) (a || b) := by
+  ext i; cases i using Fin.succRecOn <;> simp
+
+@[simp] theorem concat_and_concat (x y : BitVec w) (a b : Bool) :
+    (concat x a) &&& (concat y b) = concat (x &&& y) (a && b) := by
+  ext i; cases i using Fin.succRecOn <;> simp
+
+@[simp] theorem concat_xor_concat (x y : BitVec w) (a b : Bool) :
+    (concat x a) ^^^ (concat y b) = concat (x ^^^ y) (xor a b) := by
+  ext i; cases i using Fin.succRecOn <;> simp
+
+/-! ### add -/
+
+theorem add_def {n} (x y : BitVec n) : x + y = .ofNat n (x.toNat + y.toNat) := rfl
+
+/--
+Definition of bitvector addition as a nat.
+-/
+@[simp, bv_toNat] theorem toNat_add (x y : BitVec w) : (x + y).toNat = (x.toNat + y.toNat) % 2^w := rfl
+@[simp] theorem toFin_add (x y : BitVec w) : (x + y).toFin = toFin x + toFin y := rfl
+@[simp] theorem ofFin_add (x : Fin (2^n)) (y : BitVec n) :
+  .ofFin x + y = .ofFin (x + y.toFin) := rfl
+@[simp] theorem add_ofFin (x : BitVec n) (y : Fin (2^n)) :
+  x + .ofFin y = .ofFin (x.toFin + y) := rfl
+
+theorem ofNat_add {n} (x y : Nat) : (x + y)#n = x#n + y#n := by
+  apply eq_of_toNat_eq ; simp [BitVec.ofNat]
+
+theorem ofNat_add_ofNat {n} (x y : Nat) : x#n + y#n = (x + y)#n :=
+  (ofNat_add x y).symm
+
+protected theorem add_assoc (x y z : BitVec n) : x + y + z = x + (y + z) := by
+  apply eq_of_toNat_eq ; simp [Nat.add_assoc]
+
+protected theorem add_comm (x y : BitVec n) : x + y = y + x := by
+  simp [add_def, Nat.add_comm]
+
+@[simp] protected theorem add_zero (x : BitVec n) : x + 0#n = x := by simp [add_def]
+
+@[simp] protected theorem zero_add (x : BitVec n) : 0#n + x = x := by simp [add_def]
+
+theorem truncate_add (x y : BitVec w) (h : i ≤ w) :
+    (x + y).truncate i = x.truncate i + y.truncate i := by
+  have dvd : 2^i ∣ 2^w := Nat.pow_dvd_pow _ h
+  simp [bv_toNat, h, Nat.mod_mod_of_dvd _ dvd]
+
+@[simp, bv_toNat] theorem toInt_add (x y : BitVec w) :
+  (x + y).toInt = (x.toInt + y.toInt).bmod (2^w) := by
+  simp [toInt_eq_toNat_bmod]
+
+theorem ofInt_add {n} (x y : Int) : BitVec.ofInt n (x + y) =
+    BitVec.ofInt n x + BitVec.ofInt n y := by
+  apply eq_of_toInt_eq
+  simp
+
+/-! ### sub/neg -/
+
+theorem sub_def {n} (x y : BitVec n) : x - y = .ofNat n (x.toNat + (2^n - y.toNat)) := by rfl
+
+@[simp, bv_toNat] theorem toNat_sub {n} (x y : BitVec n) :
+  (x - y).toNat = ((x.toNat + (2^n - y.toNat)) % 2^n) := rfl
+@[simp] theorem toFin_sub (x y : BitVec n) : (x - y).toFin = toFin x - toFin y := rfl
+
+@[simp] theorem ofFin_sub (x : Fin (2^n)) (y : BitVec n) : .ofFin x - y = .ofFin (x - y.toFin) :=
+  rfl
+@[simp] theorem sub_ofFin (x : BitVec n) (y : Fin (2^n)) : x - .ofFin y = .ofFin (x.toFin - y) :=
+  rfl
+-- Remark: we don't use `[simp]` here because simproc` subsumes it for literals.
+-- If `x` and `n` are not literals, applying this theorem eagerly may not be a good idea.
+theorem ofNat_sub_ofNat {n} (x y : Nat) : x#n - y#n = .ofNat n (x + (2^n - y % 2^n)) := by
+  apply eq_of_toNat_eq ; simp [BitVec.ofNat]
+
+@[simp] protected theorem sub_zero (x : BitVec n) : x - (0#n) = x := by apply eq_of_toNat_eq ; simp
+
+@[simp] protected theorem sub_self (x : BitVec n) : x - x = 0#n := by
+  apply eq_of_toNat_eq
+  simp only [toNat_sub]
+  rw [Nat.add_sub_of_le]
+  · simp
+  · exact Nat.le_of_lt x.isLt
+
+@[simp, bv_toNat] theorem toNat_neg (x : BitVec n) : (- x).toNat = (2^n - x.toNat) % 2^n := by
+  simp [Neg.neg, BitVec.neg]
+
+theorem sub_toAdd {n} (x y : BitVec n) : x - y = x + - y := by
+  apply eq_of_toNat_eq
+  simp
+
+@[simp] theorem neg_zero (n:Nat) : -0#n = 0#n := by apply eq_of_toNat_eq ; simp
+
+theorem add_sub_cancel (x y : BitVec w) : x + y - y = x := by
+  apply eq_of_toNat_eq
+  have y_toNat_le := Nat.le_of_lt y.toNat_lt
+  rw [toNat_sub, toNat_add, Nat.mod_add_mod, Nat.add_assoc, ← Nat.add_sub_assoc y_toNat_le,
+    Nat.add_sub_cancel_left, Nat.add_mod_right, toNat_mod_cancel]
+
+theorem negOne_eq_allOnes : -1#w = allOnes w := by
+  apply eq_of_toNat_eq
+  if g : w = 0 then
+    simp [g]
+  else
+    have q : 1 < 2^w := by simp [g]
+    have r : (2^w - 1) < 2^w := by omega
+    simp [Nat.mod_eq_of_lt q, Nat.mod_eq_of_lt r]
+
+/-! ### mul -/
+
+theorem mul_def {n} {x y : BitVec n} : x * y = (ofFin <| x.toFin * y.toFin) := by rfl
+
+@[simp, bv_toNat] theorem toNat_mul (x y : BitVec n) : (x * y).toNat = (x.toNat * y.toNat) % 2 ^ n := rfl
+@[simp] theorem toFin_mul (x y : BitVec n) : (x * y).toFin = (x.toFin * y.toFin) := rfl
+
+protected theorem mul_comm (x y : BitVec w) : x * y = y * x := by
+  apply eq_of_toFin_eq; simpa using Fin.mul_comm ..
+instance : Std.Commutative (fun (x y : BitVec w) => x * y) := ⟨BitVec.mul_comm⟩
+
+protected theorem mul_assoc (x y z : BitVec w) : x * y * z = x * (y * z) := by
+  apply eq_of_toFin_eq; simpa using Fin.mul_assoc ..
+instance : Std.Associative (fun (x y : BitVec w) => x * y) := ⟨BitVec.mul_assoc⟩
+
+@[simp] protected theorem mul_one (x : BitVec w) : x * 1#w = x := by
+  cases w
+  · apply Subsingleton.elim
+  · apply eq_of_toNat_eq; simp [Nat.mod_eq_of_lt]
+
+@[simp] protected theorem one_mul (x : BitVec w) : 1#w * x = x := by
+  rw [BitVec.mul_comm, BitVec.mul_one]
+
+instance : Std.LawfulCommIdentity (fun (x y : BitVec w) => x * y) (1#w) where
+  right_id := BitVec.mul_one
+
+@[simp, bv_toNat] theorem toInt_mul (x y : BitVec w) :
+  (x * y).toInt = (x.toInt * y.toInt).bmod (2^w) := by
+  simp [toInt_eq_toNat_bmod]
+
+theorem ofInt_mul {n} (x y : Int) : BitVec.ofInt n (x * y) =
+    BitVec.ofInt n x * BitVec.ofInt n y := by
+  apply eq_of_toInt_eq
+  simp
+
+/-! ### le and lt -/
+
+@[bv_toNat] theorem le_def (x y : BitVec n) :
+  x ≤ y ↔ x.toNat ≤ y.toNat := Iff.rfl
+
+@[simp] theorem le_ofFin (x : BitVec n) (y : Fin (2^n)) :
+  x ≤ BitVec.ofFin y ↔ x.toFin ≤ y := Iff.rfl
+@[simp] theorem ofFin_le (x : Fin (2^n)) (y : BitVec n) :
+  BitVec.ofFin x ≤ y ↔ x ≤ y.toFin := Iff.rfl
+@[simp] theorem ofNat_le_ofNat {n} (x y : Nat) : (x#n) ≤ (y#n) ↔ x % 2^n ≤ y % 2^n := by
+  simp [le_def]
+
+@[bv_toNat] theorem lt_def (x y : BitVec n) :
+  x < y ↔ x.toNat < y.toNat := Iff.rfl
+
+@[simp] theorem lt_ofFin (x : BitVec n) (y : Fin (2^n)) :
+  x < BitVec.ofFin y ↔ x.toFin < y := Iff.rfl
+@[simp] theorem ofFin_lt (x : Fin (2^n)) (y : BitVec n) :
+  BitVec.ofFin x < y ↔ x < y.toFin := Iff.rfl
+@[simp] theorem ofNat_lt_ofNat {n} (x y : Nat) : (x#n) < (y#n) ↔ x % 2^n < y % 2^n := by
+  simp [lt_def]
+
+protected theorem lt_of_le_ne (x y : BitVec n) (h1 : x <= y) (h2 : ¬ x = y) : x < y := by
+  revert h1 h2
+  let ⟨x, lt⟩ := x
+  let ⟨y, lt⟩ := y
+  simp
+  exact Nat.lt_of_le_of_ne
+
+/-! ### intMax -/
+
+/-- The bitvector of width `w` that has the largest value when interpreted as an integer. -/
+def intMax (w : Nat) : BitVec w  := (2^w - 1)#w
+
+theorem getLsb_intMax_eq (w : Nat) : (intMax w).getLsb i = decide (i < w) := by
+  simp [intMax, getLsb]
+
+theorem toNat_intMax_eq : (intMax w).toNat = 2^w - 1 := by
+  have h : 2^w - 1 < 2^w := by
+    have pos : 2^w > 0 := Nat.pow_pos (by decide)
+    omega
+  simp [intMax, Nat.shiftLeft_eq, Nat.one_mul, natCast_eq_ofNat, toNat_ofNat, Nat.mod_eq_of_lt h]
+
+/-! ### ofBoolList -/
+
+@[simp] theorem getMsb_ofBoolListBE : (ofBoolListBE bs).getMsb i = bs.getD i false := by
+  induction bs generalizing i <;> cases i <;> simp_all [ofBoolListBE]
+
+@[simp] theorem getLsb_ofBoolListBE :
+    (ofBoolListBE bs).getLsb i = (decide (i < bs.length) && bs.getD (bs.length - 1 - i) false) := by
+  simp [getLsb_eq_getMsb]
+
+@[simp] theorem getLsb_ofBoolListLE : (ofBoolListLE bs).getLsb i = bs.getD i false := by
+  induction bs generalizing i <;> cases i <;> simp_all [ofBoolListLE]
+
+@[simp] theorem getMsb_ofBoolListLE :
+    (ofBoolListLE bs).getMsb i = (decide (i < bs.length) && bs.getD (bs.length - 1 - i) false) := by
+  simp [getMsb_eq_getLsb]
+
+end BitVec

src/Init/Data/Bool.lean

@@ -0,0 +1,513 @@
+/-
+Copyright (c) 2023 F. G. Dorais. No rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: F. G. Dorais
+-/
+prelude
+import Init.BinderPredicates
+
+/-- Boolean exclusive or -/
+abbrev xor : Bool → Bool → Bool := bne
+
+namespace Bool
+
+/- Namespaced versions that can be used instead of prefixing `_root_` -/
+@[inherit_doc not] protected abbrev not := not
+@[inherit_doc or]  protected abbrev or  := or
+@[inherit_doc and] protected abbrev and := and
+@[inherit_doc xor] protected abbrev xor := xor
+
+instance (p : Bool → Prop) [inst : DecidablePred p] : Decidable (∀ x, p x) :=
+  match inst true, inst false with
+  | isFalse ht, _ => isFalse fun h => absurd (h _) ht
+  | _, isFalse hf => isFalse fun h => absurd (h _) hf
+  | isTrue ht, isTrue hf => isTrue fun | true => ht | false => hf
+
+instance (p : Bool → Prop) [inst : DecidablePred p] : Decidable (∃ x, p x) :=
+  match inst true, inst false with
+  | isTrue ht, _ => isTrue ⟨_, ht⟩
+  | _, isTrue hf => isTrue ⟨_, hf⟩
+  | isFalse ht, isFalse hf => isFalse fun | ⟨true, h⟩ => absurd h ht | ⟨false, h⟩ => absurd h hf
+
+@[simp] theorem default_bool : default = false := rfl
+
+instance : LE Bool := ⟨(. → .)⟩
+instance : LT Bool := ⟨(!. && .)⟩
+
+instance (x y : Bool) : Decidable (x ≤ y) := inferInstanceAs (Decidable (x → y))
+instance (x y : Bool) : Decidable (x < y) := inferInstanceAs (Decidable (!x && y))
+
+instance : Max Bool := ⟨or⟩
+instance : Min Bool := ⟨and⟩
+
+theorem false_ne_true : false ≠ true := Bool.noConfusion
+
+theorem eq_false_or_eq_true : (b : Bool) → b = true ∨ b = false := by decide
+
+theorem eq_false_iff : {b : Bool} → b = false ↔ b ≠ true := by decide
+
+theorem ne_false_iff : {b : Bool} → b ≠ false ↔ b = true := by decide
+
+theorem eq_iff_iff {a b : Bool} : a = b ↔ (a ↔ b) := by cases b <;> simp
+
+@[simp] theorem decide_eq_true  {b : Bool} [Decidable (b = true)]  : decide (b = true)  =  b := by cases b <;> simp
+@[simp] theorem decide_eq_false {b : Bool} [Decidable (b = false)] : decide (b = false) = !b := by cases b <;> simp
+@[simp] theorem decide_true_eq  {b : Bool} [Decidable (true = b)]  : decide (true  = b) =  b := by cases b <;> simp
+@[simp] theorem decide_false_eq {b : Bool} [Decidable (false = b)] : decide (false = b) = !b := by cases b <;> simp
+
+/-! ### and -/
+
+@[simp] theorem and_self_left  : ∀(a b : Bool), (a && (a && b)) = (a && b) := by decide
+@[simp] theorem and_self_right : ∀(a b : Bool), ((a && b) && b) = (a && b) := by decide
+
+@[simp] theorem not_and_self : ∀ (x : Bool), (!x && x) = false := by decide
+@[simp] theorem and_not_self : ∀ (x : Bool), (x && !x) = false := by decide
+
+/-
+Added for confluence with `not_and_self` `and_not_self` on term
+`(b && !b) = true` due to reductions:
+
+1. `(b = true ∨ !b = true)` via `Bool.and_eq_true`
+2. `false = true` via `Bool.and_not_self`
+-/
+@[simp] theorem eq_true_and_eq_false_self : ∀(b : Bool), (b = true ∧ b = false) ↔ False := by decide
+@[simp] theorem eq_false_and_eq_true_self : ∀(b : Bool), (b = false ∧ b = true) ↔ False := by decide
+
+theorem and_comm : ∀ (x y : Bool), (x && y) = (y && x) := by decide
+
+theorem and_left_comm : ∀ (x y z : Bool), (x && (y && z)) = (y && (x && z)) := by decide
+theorem and_right_comm : ∀ (x y z : Bool), ((x && y) && z) = ((x && z) && y) := by decide
+
+/-
+Bool version `and_iff_left_iff_imp`.
+
+Needed for confluence of term `(a && b) ↔ a` which reduces to `(a && b) = a` via
+`Bool.coe_iff_coe` and `a → b` via `Bool.and_eq_true` and
+`and_iff_left_iff_imp`.
+-/
+@[simp] theorem and_iff_left_iff_imp  : ∀(a b : Bool), ((a && b) = a) ↔ (a → b) := by decide
+@[simp] theorem and_iff_right_iff_imp : ∀(a b : Bool), ((a && b) = b) ↔ (b → a) := by decide
+@[simp] theorem iff_self_and : ∀(a b : Bool), (a = (a && b)) ↔ (a → b) := by decide
+@[simp] theorem iff_and_self : ∀(a b : Bool), (b = (a && b)) ↔ (b → a) := by decide
+
+/-! ### or -/
+
+@[simp] theorem or_self_left  : ∀(a b : Bool), (a || (a || b)) = (a || b) := by decide
+@[simp] theorem or_self_right : ∀(a b : Bool), ((a || b) || b) = (a || b) := by decide
+
+@[simp] theorem not_or_self : ∀ (x : Bool), (!x || x) = true := by decide
+@[simp] theorem or_not_self : ∀ (x : Bool), (x || !x) = true := by decide
+
+/-
+Added for confluence with `not_or_self` `or_not_self` on term
+`(b || !b) = true` due to reductions:
+1. `(b = true ∨ !b = true)` via `Bool.or_eq_true`
+2. `true = true` via `Bool.or_not_self`
+-/
+@[simp] theorem eq_true_or_eq_false_self : ∀(b : Bool), (b = true ∨ b = false) ↔ True := by decide
+@[simp] theorem eq_false_or_eq_true_self : ∀(b : Bool), (b = false ∨ b = true) ↔ True := by decide
+
+/-
+Bool version `or_iff_left_iff_imp`.
+
+Needed for confluence of term `(a || b) ↔ a` which reduces to `(a || b) = a` via
+`Bool.coe_iff_coe` and `a → b` via `Bool.or_eq_true` and
+`and_iff_left_iff_imp`.
+-/
+@[simp] theorem or_iff_left_iff_imp  : ∀(a b : Bool), ((a || b) = a) ↔ (b → a) := by decide
+@[simp] theorem or_iff_right_iff_imp : ∀(a b : Bool), ((a || b) = b) ↔ (a → b) := by decide
+@[simp] theorem iff_self_or : ∀(a b : Bool), (a = (a || b)) ↔ (b → a) := by decide
+@[simp] theorem iff_or_self : ∀(a b : Bool), (b = (a || b)) ↔ (a → b) := by decide
+
+theorem or_comm : ∀ (x y : Bool), (x || y) = (y || x) := by decide
+
+theorem or_left_comm : ∀ (x y z : Bool), (x || (y || z)) = (y || (x || z)) := by decide
+theorem or_right_comm : ∀ (x y z : Bool), ((x || y) || z) = ((x || z) || y) := by decide
+
+/-! ### distributivity -/
+
+theorem and_or_distrib_left  : ∀ (x y z : Bool), (x && (y || z)) = (x && y || x && z) := by decide
+theorem and_or_distrib_right : ∀ (x y z : Bool), ((x || y) && z) = (x && z || y && z) := by decide
+
+theorem or_and_distrib_left  : ∀ (x y z : Bool), (x || y && z) = ((x || y) && (x || z)) := by decide
+theorem or_and_distrib_right : ∀ (x y z : Bool), (x && y || z) = ((x || z) && (y || z)) := by decide
+
+theorem and_xor_distrib_left : ∀ (x y z : Bool), (x && xor y z) = xor (x && y) (x && z) := by decide
+theorem and_xor_distrib_right : ∀ (x y z : Bool), (xor x y && z) = xor (x && z) (y && z) := by decide
+
+/-- De Morgan's law for boolean and -/
+@[simp] theorem not_and : ∀ (x y : Bool), (!(x && y)) = (!x || !y) := by decide
+
+/-- De Morgan's law for boolean or -/
+@[simp] theorem not_or : ∀ (x y : Bool), (!(x || y)) = (!x && !y) := by decide
+
+theorem and_eq_true_iff (x y : Bool) : (x && y) = true ↔ x = true ∧ y = true :=
+  Iff.of_eq (and_eq_true x y)
+
+theorem and_eq_false_iff : ∀ (x y : Bool), (x && y) = false ↔ x = false ∨ y = false := by decide
+
+/-
+New simp rule that replaces `Bool.and_eq_false_eq_eq_false_or_eq_false` in
+Mathlib due to confluence:
+
+Consider the term: `¬((b && c) = true)`:
+
+1. Reduces to `((b && c) = false)` via `Bool.not_eq_true`
+2. Reduces to `¬(b = true ∧ c = true)` via `Bool.and_eq_true`.
+
+
+1. Further reduces to `b = false ∨ c = false` via `Bool.and_eq_false_eq_eq_false_or_eq_false`.
+2. Further reduces to `b = true → c = false` via `not_and` and `Bool.not_eq_true`.
+-/
+@[simp] theorem and_eq_false_imp : ∀ (x y : Bool), (x && y) = false ↔ (x = true → y = false) := by decide
+
+@[simp] theorem or_eq_true_iff : ∀ (x y : Bool), (x || y) = true ↔ x = true ∨ y = true := by decide
+
+@[simp] theorem or_eq_false_iff : ∀ (x y : Bool), (x || y) = false ↔ x = false ∧ y = false := by decide
+
+/-! ### eq/beq/bne -/
+
+/--
+These two rules follow trivially by simp, but are needed to avoid non-termination
+in false_eq and true_eq.
+-/
+@[simp] theorem false_eq_true : (false = true) = False := by simp
+@[simp] theorem true_eq_false : (true = false) = False := by simp
+
+-- The two lemmas below normalize terms with a constant to the
+-- right-hand side but risk non-termination if `false_eq_true` and
+-- `true_eq_false` are disabled.
+@[simp low] theorem false_eq (b : Bool) : (false = b) = (b = false) := by
+  cases b <;> simp
+
+@[simp low] theorem true_eq (b : Bool) : (true = b) = (b = true) := by
+  cases b <;> simp
+
+@[simp] theorem true_beq  : ∀b, (true  == b) =  b := by decide
+@[simp] theorem false_beq : ∀b, (false == b) = !b := by decide
+@[simp] theorem beq_true  : ∀b, (b == true)  =  b := by decide
+@[simp] theorem beq_false : ∀b, (b == false) = !b := by decide
+
+@[simp] theorem true_bne  : ∀(b : Bool), (true  != b) = !b := by decide
+@[simp] theorem false_bne : ∀(b : Bool), (false != b) =  b := by decide
+@[simp] theorem bne_true  : ∀(b : Bool), (b != true)  = !b := by decide
+@[simp] theorem bne_false : ∀(b : Bool), (b != false) =  b := by decide
+
+@[simp] theorem not_beq_self : ∀ (x : Bool), ((!x) == x) = false := by decide
+@[simp] theorem beq_not_self : ∀ (x : Bool), (x   == !x) = false := by decide
+
+@[simp] theorem not_bne_self : ∀ (x : Bool), ((!x) != x) = true := by decide
+@[simp] theorem bne_not_self : ∀ (x : Bool), (x   != !x) = true := by decide
+
+/-
+Added for equivalence with `Bool.not_beq_self` and needed for confluence
+due to `beq_iff_eq`.
+-/
+@[simp] theorem not_eq_self : ∀(b : Bool), ((!b) = b) ↔ False := by decide
+@[simp] theorem eq_not_self : ∀(b : Bool), (b = (!b)) ↔ False := by decide
+
+@[simp] theorem beq_self_left  : ∀(a b : Bool), (a == (a == b)) = b := by decide
+@[simp] theorem beq_self_right : ∀(a b : Bool), ((a == b) == b) = a := by decide
+@[simp] theorem bne_self_left  : ∀(a b : Bool), (a != (a != b)) = b := by decide
+@[simp] theorem bne_self_right : ∀(a b : Bool), ((a != b) != b) = a := by decide
+
+@[simp] theorem not_bne_not : ∀ (x y : Bool), ((!x) != (!y)) = (x != y) := by decide
+
+@[simp] theorem bne_assoc : ∀ (x y z : Bool), ((x != y) != z) = (x != (y != z)) := by decide
+
+@[simp] theorem bne_left_inj  : ∀ (x y z : Bool), (x != y) = (x != z) ↔ y = z := by decide
+@[simp] theorem bne_right_inj : ∀ (x y z : Bool), (x != z) = (y != z) ↔ x = y := by decide
+
+/-! ### coercision related normal forms -/
+
+theorem beq_eq_decide_eq [BEq α] [LawfulBEq α] [DecidableEq α] (a b : α) :
+    (a == b) = decide (a = b) := by
+  cases h : a == b
+  · simp [ne_of_beq_false h]
+  · simp [eq_of_beq h]
+
+@[simp] theorem not_eq_not : ∀ {a b : Bool}, ¬a = !b ↔ a = b := by decide
+
+@[simp] theorem not_not_eq : ∀ {a b : Bool}, ¬(!a) = b ↔ a = b := by decide
+
+@[simp] theorem coe_iff_coe : ∀(a b : Bool), (a ↔ b) ↔ a = b := by decide
+
+@[simp] theorem coe_true_iff_false  : ∀(a b : Bool), (a ↔ b = false) ↔ a = (!b) := by decide
+@[simp] theorem coe_false_iff_true  : ∀(a b : Bool), (a = false ↔ b) ↔ (!a) = b := by decide
+@[simp] theorem coe_false_iff_false : ∀(a b : Bool), (a = false ↔ b = false) ↔ (!a) = (!b) := by decide
+
+/-! ### beq properties -/
+
+theorem beq_comm {α} [BEq α] [LawfulBEq α] {a b : α} : (a == b) = (b == a) :=
+  (Bool.coe_iff_coe (a == b) (b == a)).mp (by simp [@eq_comm α])
+
+/-! ### xor -/
+
+theorem false_xor : ∀ (x : Bool), xor false x = x := false_bne
+
+theorem xor_false : ∀ (x : Bool), xor x false = x := bne_false
+
+theorem true_xor : ∀ (x : Bool), xor true x = !x := true_bne
+
+theorem xor_true : ∀ (x : Bool), xor x true = !x := bne_true
+
+theorem not_xor_self : ∀ (x : Bool), xor (!x) x = true := not_bne_self
+
+theorem xor_not_self : ∀ (x : Bool), xor x (!x) = true := bne_not_self
+
+theorem not_xor : ∀ (x y : Bool), xor (!x) y = !(xor x y) := by decide
+
+theorem xor_not : ∀ (x y : Bool), xor x (!y) = !(xor x y) := by decide
+
+theorem not_xor_not : ∀ (x y : Bool), xor (!x) (!y) = (xor x y) := not_bne_not
+
+theorem xor_self : ∀ (x : Bool), xor x x = false := by decide
+
+theorem xor_comm : ∀ (x y : Bool), xor x y = xor y x := by decide
+
+theorem xor_left_comm : ∀ (x y z : Bool), xor x (xor y z) = xor y (xor x z) := by decide
+
+theorem xor_right_comm : ∀ (x y z : Bool), xor (xor x y) z = xor (xor x z) y := by decide
+
+theorem xor_assoc : ∀ (x y z : Bool), xor (xor x y) z = xor x (xor y z) := bne_assoc
+
+theorem xor_left_inj : ∀ (x y z : Bool), xor x y = xor x z ↔ y = z := bne_left_inj
+
+theorem xor_right_inj : ∀ (x y z : Bool), xor x z = xor y z ↔ x = y := bne_right_inj
+
+/-! ### le/lt -/
+
+@[simp] protected theorem le_true : ∀ (x : Bool), x ≤ true := by decide
+
+@[simp] protected theorem false_le : ∀ (x : Bool), false ≤ x := by decide
+
+@[simp] protected theorem le_refl : ∀ (x : Bool), x ≤ x := by decide
+
+@[simp] protected theorem lt_irrefl : ∀ (x : Bool), ¬ x < x := by decide
+
+protected theorem le_trans : ∀ {x y z : Bool}, x ≤ y → y ≤ z → x ≤ z := by decide
+
+protected theorem le_antisymm : ∀ {x y : Bool}, x ≤ y → y ≤ x → x = y := by decide
+
+protected theorem le_total : ∀ (x y : Bool), x ≤ y ∨ y ≤ x := by decide
+
+protected theorem lt_asymm : ∀ {x y : Bool}, x < y → ¬ y < x := by decide
+
+protected theorem lt_trans : ∀ {x y z : Bool}, x < y → y < z → x < z := by decide
+
+protected theorem lt_iff_le_not_le : ∀ {x y : Bool}, x < y ↔ x ≤ y ∧ ¬ y ≤ x := by decide
+
+protected theorem lt_of_le_of_lt : ∀ {x y z : Bool}, x ≤ y → y < z → x < z := by decide
+
+protected theorem lt_of_lt_of_le : ∀ {x y z : Bool}, x < y → y ≤ z → x < z := by decide
+
+protected theorem le_of_lt : ∀ {x y : Bool}, x < y → x ≤ y := by decide
+
+protected theorem le_of_eq : ∀ {x y : Bool}, x = y → x ≤ y := by decide
+
+protected theorem ne_of_lt : ∀ {x y : Bool}, x < y → x ≠ y := by decide
+
+protected theorem lt_of_le_of_ne : ∀ {x y : Bool}, x ≤ y → x ≠ y → x < y := by decide
+
+protected theorem le_of_lt_or_eq : ∀ {x y : Bool}, x < y ∨ x = y → x ≤ y := by decide
+
+protected theorem eq_true_of_true_le : ∀ {x : Bool}, true ≤ x → x = true := by decide
+
+protected theorem eq_false_of_le_false : ∀ {x : Bool}, x ≤ false → x = false := by decide
+
+/-! ### min/max -/
+
+@[simp] protected theorem max_eq_or : max = or := rfl
+
+@[simp] protected theorem min_eq_and : min = and := rfl
+
+/-! ### injectivity lemmas -/
+
+theorem not_inj : ∀ {x y : Bool}, (!x) = (!y) → x = y := by decide
+
+theorem not_inj_iff : ∀ {x y : Bool}, (!x) = (!y) ↔ x = y := by decide
+
+theorem and_or_inj_right : ∀ {m x y : Bool}, (x && m) = (y && m) → (x || m) = (y || m) → x = y := by
+  decide
+
+theorem and_or_inj_right_iff :
+    ∀ {m x y : Bool}, (x && m) = (y && m) ∧ (x || m) = (y || m) ↔ x = y := by decide
+
+theorem and_or_inj_left : ∀ {m x y : Bool}, (m && x) = (m && y) → (m || x) = (m || y) → x = y := by
+  decide
+
+theorem and_or_inj_left_iff :
+    ∀ {m x y : Bool}, (m && x) = (m && y) ∧ (m || x) = (m || y) ↔ x = y := by decide
+
+/-! ## toNat -/
+
+/-- convert a `Bool` to a `Nat`, `false -> 0`, `true -> 1` -/
+def toNat (b:Bool) : Nat := cond b 1 0
+
+@[simp] theorem toNat_false : false.toNat = 0 := rfl
+
+@[simp] theorem toNat_true : true.toNat = 1 := rfl
+
+theorem toNat_le (c : Bool) : c.toNat ≤ 1 := by
+  cases c <;> trivial
+
+@[deprecated toNat_le] abbrev toNat_le_one := toNat_le
+
+theorem toNat_lt (b : Bool) : b.toNat < 2 :=
+  Nat.lt_succ_of_le (toNat_le _)
+
+@[simp] theorem toNat_eq_zero (b : Bool) : b.toNat = 0 ↔ b = false := by
+  cases b <;> simp
+@[simp] theorem toNat_eq_one  (b : Bool) : b.toNat = 1 ↔ b = true := by
+  cases b <;> simp
+
+/-! ### ite -/
+
+@[simp] theorem if_true_left  (p : Prop) [h : Decidable p] (f : Bool) :
+    (ite p true f) = (p || f) := by cases h with | _ p => simp [p]
+
+@[simp] theorem if_false_left  (p : Prop) [h : Decidable p] (f : Bool) :
+    (ite p false f) = (!p && f) := by cases h with | _ p => simp [p]
+
+@[simp] theorem if_true_right  (p : Prop) [h : Decidable p] (t : Bool) :
+    (ite p t true) = (!(p : Bool) || t) := by cases h with | _ p => simp [p]
+
+@[simp] theorem if_false_right  (p : Prop) [h : Decidable p] (t : Bool) :
+    (ite p t false) = (p && t) := by cases h with | _ p => simp [p]
+
+@[simp] theorem ite_eq_true_distrib (p : Prop) [h : Decidable p] (t f : Bool) :
+    (ite p t f = true) = ite p (t = true) (f = true) := by
+  cases h with | _ p => simp [p]
+
+@[simp] theorem ite_eq_false_distrib (p : Prop) [h : Decidable p] (t f : Bool) :
+    (ite p t f = false) = ite p (t = false) (f = false) := by
+  cases h with | _ p => simp [p]
+
+/-
+`not_ite_eq_true_eq_true` and related theorems below are added for
+non-confluence.  A motivating example is
+`¬((if u then b else c) = true)`.
+
+This reduces to:
+1. `¬((if u then (b = true) else (c = true))` via `ite_eq_true_distrib`
+2. `(if u then b c) = false)` via `Bool.not_eq_true`.
+
+Similar logic holds for `¬((if u then b else c) = false)` and related
+lemmas.
+-/
+
+@[simp]
+theorem not_ite_eq_true_eq_true (p : Prop) [h : Decidable p] (b c : Bool) :
+  ¬(ite p (b = true) (c = true)) ↔ (ite p (b = false) (c = false)) := by
+  cases h with | _ p => simp [p]
+
+@[simp]
+theorem not_ite_eq_false_eq_false (p : Prop) [h : Decidable p] (b c : Bool) :
+  ¬(ite p (b = false) (c = false)) ↔ (ite p (b = true) (c = true)) := by
+  cases h with | _ p => simp [p]
+
+@[simp]
+theorem not_ite_eq_true_eq_false (p : Prop) [h : Decidable p] (b c : Bool) :
+  ¬(ite p (b = true) (c = false)) ↔ (ite p (b = false) (c = true)) := by
+  cases h with | _ p => simp [p]
+
+@[simp]
+theorem not_ite_eq_false_eq_true (p : Prop) [h : Decidable p] (b c : Bool) :
+  ¬(ite p (b = false) (c = true)) ↔ (ite p (b = true) (c = false)) := by
+  cases h with | _ p => simp [p]
+
+/-
+Added for confluence between `if_true_left` and `ite_false_same` on
+`if b = true then True else b = true`
+-/
+@[simp] theorem eq_false_imp_eq_true : ∀(b:Bool), (b = false → b = true) ↔ (b = true) := by decide
+
+/-
+Added for confluence between `if_true_left` and `ite_false_same` on
+`if b = false then True else b = false`
+-/
+@[simp] theorem eq_true_imp_eq_false : ∀(b:Bool), (b = true → b = false) ↔ (b = false) := by decide
+
+
+/-! ### cond -/
+
+theorem cond_eq_ite {α} (b : Bool) (t e : α) : cond b t e = if b then t else e := by
+  cases b <;> simp
+
+theorem cond_eq_if : (bif b then x else y) = (if b then x else y) := cond_eq_ite b x y
+
+@[simp] theorem cond_not (b : Bool) (t e : α) : cond (!b) t e = cond b e t := by
+  cases b <;> rfl
+
+@[simp] theorem cond_self (c : Bool) (t : α) : cond c t t = t := by cases c <;> rfl
+
+/-
+This is a simp rule in Mathlib, but results in non-confluence that is difficult
+to fix as decide distributes over propositions. As an example, observe that
+`cond (decide (p ∧ q)) t f` could simplify to either:
+
+* `if p ∧ q then t else f` via `Bool.cond_decide` or
+* `cond (decide p && decide q) t f` via `Bool.decide_and`.
+
+A possible approach to improve normalization between `cond` and `ite` would be
+to completely simplify away `cond` by making `cond_eq_ite` a `simp` rule, but
+that has not been taken since it could surprise users to migrate pure `Bool`
+operations like `cond` to a mix of `Prop` and `Bool`.
+-/
+theorem cond_decide {α} (p : Prop) [Decidable p] (t e : α) :
+    cond (decide p) t e = if p then t else e := by
+  simp [cond_eq_ite]
+
+@[simp] theorem cond_eq_ite_iff (a : Bool) (p : Prop) [h : Decidable p] (x y u v : α) :
+  (cond a x y = ite p u v) ↔ ite a x y = ite p u v := by
+  simp [Bool.cond_eq_ite]
+
+@[simp] theorem ite_eq_cond_iff (p : Prop) [h : Decidable p] (a : Bool) (x y u v : α) :
+  (ite p x y = cond a u v) ↔ ite p x y = ite a u v := by
+  simp [Bool.cond_eq_ite]
+
+@[simp] theorem cond_eq_true_distrib : ∀(c t f : Bool),
+    (cond c t f = true) = ite (c = true) (t = true) (f = true) := by
+  decide
+
+@[simp] theorem cond_eq_false_distrib : ∀(c t f : Bool),
+    (cond c t f = false) = ite (c = true) (t = false) (f = false) := by decide
+
+protected theorem cond_true  {α : Type u} {a b : α} : cond true  a b = a := cond_true  a b
+protected theorem cond_false {α : Type u} {a b : α} : cond false a b = b := cond_false a b
+
+@[simp] theorem cond_true_left   : ∀(c f : Bool), cond c true f  = ( c || f) := by decide
+@[simp] theorem cond_false_left  : ∀(c f : Bool), cond c false f = (!c && f) := by decide
+@[simp] theorem cond_true_right  : ∀(c t : Bool), cond c t true  = (!c || t) := by decide
+@[simp] theorem cond_false_right : ∀(c t : Bool), cond c t false = ( c && t) := by decide
+
+@[simp] theorem cond_true_same  : ∀(c b : Bool), cond c c b = (c || b) := by decide
+@[simp] theorem cond_false_same : ∀(c b : Bool), cond c b c = (c && b) := by decide
+
+/-# decidability -/
+
+protected theorem decide_coe (b : Bool) [Decidable (b = true)] : decide (b = true) = b := decide_eq_true
+
+@[simp] theorem decide_and (p q : Prop) [dpq : Decidable (p ∧ q)] [dp : Decidable p] [dq : Decidable q] :
+    decide (p ∧ q) = (p && q) := by
+  cases dp with | _ p => simp [p]
+
+@[simp] theorem decide_or (p q : Prop) [dpq : Decidable (p ∨ q)] [dp : Decidable p] [dq : Decidable q] :
+    decide (p ∨ q) = (p || q) := by
+  cases dp with | _ p => simp [p]
+
+@[simp] theorem decide_iff_dist (p q : Prop) [dpq : Decidable (p ↔ q)] [dp : Decidable p] [dq : Decidable q] :
+    decide (p ↔ q) = (decide p == decide q) := by
+  cases dp with | _ p => simp [p]
+
+end Bool
+
+export Bool (cond_eq_if)
+
+/-! ### decide -/
+
+@[simp] theorem false_eq_decide_iff {p : Prop} [h : Decidable p] : false = decide p ↔ ¬p := by
+  cases h with | _ q => simp [q]
+
+@[simp] theorem true_eq_decide_iff {p : Prop} [h : Decidable p] : true = decide p ↔ p := by
+  cases h with | _ q => simp [q]

src/Init/Data/ByteArray/Basic.lean

@@ -52,9 +52,13 @@ def get : (a : @& ByteArray) → (@& Fin a.size) → UInt8
 instance : GetElem ByteArray Nat UInt8 fun xs i => i < xs.size where
   getElem xs i h := xs.get ⟨i, h⟩
 
+instance : LawfulGetElem ByteArray Nat UInt8 fun xs i => i < xs.size where
+
 instance : GetElem ByteArray USize UInt8 fun xs i => i.val < xs.size where
   getElem xs i h := xs.uget i h
 
+instance : LawfulGetElem ByteArray USize UInt8 fun xs i => i.val < xs.size where
+
 @[extern "lean_byte_array_set"]
 def set! : ByteArray → (@& Nat) → UInt8 → ByteArray
   | ⟨bs⟩, i, b => ⟨bs.set! i b⟩
@@ -195,18 +199,6 @@ instance : ToString ByteArray := ⟨fun bs => bs.toList.toString⟩
 
 /-- Interpret a `ByteArray` of size 8 as a little-endian `UInt64`. -/
 def ByteArray.toUInt64LE! (bs : ByteArray) : UInt64 :=
-  assert! bs.size == 8
-  (bs.get! 0).toUInt64 <<< 0x38 |||
-  (bs.get! 1).toUInt64 <<< 0x30 |||
-  (bs.get! 2).toUInt64 <<< 0x28 |||
-  (bs.get! 3).toUInt64 <<< 0x20 |||
-  (bs.get! 4).toUInt64 <<< 0x18 |||
-  (bs.get! 5).toUInt64 <<< 0x10 |||
-  (bs.get! 6).toUInt64 <<< 0x8  |||
-  (bs.get! 7).toUInt64
-
-/-- Interpret a `ByteArray` of size 8 as a big-endian `UInt64`. -/
-def ByteArray.toUInt64BE! (bs : ByteArray) : UInt64 :=
   assert! bs.size == 8
   (bs.get! 7).toUInt64 <<< 0x38 |||
   (bs.get! 6).toUInt64 <<< 0x30 |||
@@ -216,3 +208,15 @@ def ByteArray.toUInt64BE! (bs : ByteArray) : UInt64 :=
   (bs.get! 2).toUInt64 <<< 0x10 |||
   (bs.get! 1).toUInt64 <<< 0x8  |||
   (bs.get! 0).toUInt64
+
+/-- Interpret a `ByteArray` of size 8 as a big-endian `UInt64`. -/
+def ByteArray.toUInt64BE! (bs : ByteArray) : UInt64 :=
+  assert! bs.size == 8
+  (bs.get! 0).toUInt64 <<< 0x38 |||
+  (bs.get! 1).toUInt64 <<< 0x30 |||
+  (bs.get! 2).toUInt64 <<< 0x28 |||
+  (bs.get! 3).toUInt64 <<< 0x20 |||
+  (bs.get! 4).toUInt64 <<< 0x18 |||
+  (bs.get! 5).toUInt64 <<< 0x10 |||
+  (bs.get! 6).toUInt64 <<< 0x8  |||
+  (bs.get! 7).toUInt64

src/Init/Data/Cast.lean

@@ -0,0 +1,72 @@
+/-
+Copyright (c) 2014 Mario Carneiro. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Mario Carneiro, Gabriel Ebner
+-/
+prelude
+import Init.Coe
+
+/-!
+# `NatCast`
+
+We introduce the typeclass `NatCast R` for a type `R` with a "canonical
+homomorphism" `Nat → R`. The typeclass carries the data of the function,
+but no required axioms.
+
+This typeclass was introduced to support a uniform `simp` normal form
+for such morphisms.
+
+Without such a typeclass, we would have specific coercions such as
+`Int.ofNat`, but also later the generic coercion from `Nat` into any
+Mathlib semiring (including `Int`), and we would need to use `simp` to
+move between them. However `simp` lemmas expressed using a non-normal
+form on the LHS would then not fire.
+
+Typically different instances of this class for the same target type `R`
+are definitionally equal, and so differences in the instance do not
+block `simp` or `rw`.
+
+This logic also applies to `Int` and so we also introduce `IntCast` alongside
+`Int.
+
+## Note about coercions into arbitrary types:
+
+Coercions such as `Nat.cast` that go from a concrete structure such as
+`Nat` to an arbitrary type `R` should be set up as follows:
+```lean
+instance : CoeTail Nat R where coe := ...
+instance : CoeHTCT Nat R where coe := ...
+```
+
+It needs to be `CoeTail` instead of `Coe` because otherwise type-class
+inference would loop when constructing the transitive coercion `Nat →
+Nat → Nat → ...`. Sometimes we also need to declare the `CoeHTCT`
+instance if we need to shadow another coercion.
+-/
+
+/-- Type class for the canonical homomorphism `Nat → R`. -/
+class NatCast (R : Type u) where
+  /-- The canonical map `Nat → R`. -/
+  protected natCast : Nat → R
+
+instance : NatCast Nat where natCast n := n
+
+/--
+Canonical homomorphism from `Nat` to a type `R`.
+
+It contains just the function, with no axioms.
+In practice, the target type will likely have a (semi)ring structure,
+and this homomorphism should be a ring homomorphism.
+
+The prototypical example is `Int.ofNat`.
+
+This class and `IntCast` exist to allow different libraries with their own types that can be notated as natural numbers to have consistent `simp` normal forms without needing to create coercion simplification sets that are aware of all combinations. Libraries should make it easy to work with `NatCast` where possible. For instance, in Mathlib there will be such a homomorphism (and thus a `NatCast R` instance) whenever `R` is an additive monoid with a `1`.
+-/
+@[coe, reducible, match_pattern] protected def Nat.cast {R : Type u} [NatCast R] : Nat → R :=
+  NatCast.natCast
+
+-- see the notes about coercions into arbitrary types in the module doc-string
+instance [NatCast R] : CoeTail Nat R where coe := Nat.cast
+
+-- see the notes about coercions into arbitrary types in the module doc-string
+instance [NatCast R] : CoeHTCT Nat R where coe := Nat.cast

src/Init/Data/Channel.lean

@@ -41,7 +41,7 @@ Sends a message on an `Channel`.
 
 This function does not block.
 -/
-def Channel.send (v : α) (ch : Channel α) : BaseIO Unit :=
+def Channel.send (ch : Channel α) (v : α) : BaseIO Unit :=
   ch.atomically do
     let st ← get
     if st.closed then return

src/Init/Data/Fin.lean

@@ -6,3 +6,6 @@ Author: Leonardo de Moura
 prelude
 import Init.Data.Fin.Basic
 import Init.Data.Fin.Log2
+import Init.Data.Fin.Iterate
+import Init.Data.Fin.Fold
+import Init.Data.Fin.Lemmas

src/Init/Data/Fin/Basic.lean

@@ -1,12 +1,10 @@
 /-
 Copyright (c) 2016 Microsoft Corporation. All rights reserved.
 Released under Apache 2.0 license as described in the file LICENSE.
-Author: Leonardo de Moura
+Author: Leonardo de Moura, Robert Y. Lewis, Keeley Hoek, Mario Carneiro
 -/
 prelude
-import Init.Data.Nat.Div
-import Init.Data.Nat.Bitwise
-import Init.Coe
+import Init.Data.Nat.Bitwise.Basic
 
 open Nat
 
@@ -15,17 +13,40 @@ namespace Fin
 instance coeToNat : CoeOut (Fin n) Nat :=
   ⟨fun v => v.val⟩
 
+/--
+From the empty type `Fin 0`, any desired result `α` can be derived. This is simlar to `Empty.elim`.
+-/
 def elim0.{u} {α : Sort u} : Fin 0 → α
   | ⟨_, h⟩ => absurd h (not_lt_zero _)
 
+/--
+Returns the successor of the argument.
+
+The bound in the result type is increased:
+```
+(2 : Fin 3).succ = (3 : Fin 4)
+```
+This differs from addition, which wraps around:
+```
+(2 : Fin 3) + 1 = (0 : Fin 3)
+```
+-/
 def succ : Fin n → Fin n.succ
   | ⟨i, h⟩ => ⟨i+1, Nat.succ_lt_succ h⟩
 
 variable {n : Nat}
 
+/--
+Returns `a` modulo `n + 1` as a `Fin n.succ`.
+-/
 protected def ofNat {n : Nat} (a : Nat) : Fin n.succ :=
   ⟨a % (n+1), Nat.mod_lt _ (Nat.zero_lt_succ _)⟩
 
+/--
+Returns `a` modulo `n` as a `Fin n`.
+
+The assumption `n > 0` ensures that `Fin n` is nonempty.
+-/
 protected def ofNat' {n : Nat} (a : Nat) (h : n > 0) : Fin n :=
   ⟨a % n, Nat.mod_lt _ h⟩
 
@@ -35,12 +56,15 @@ private theorem mlt {b : Nat} : {a : Nat} → a < n → b % n < n
     have : n > 0 := Nat.lt_trans (Nat.zero_lt_succ _) h;
     Nat.mod_lt _ this
 
+/-- Addition modulo `n` -/
 protected def add : Fin n → Fin n → Fin n
   | ⟨a, h⟩, ⟨b, _⟩ => ⟨(a + b) % n, mlt h⟩
 
+/-- Multiplication modulo `n` -/
 protected def mul : Fin n → Fin n → Fin n
   | ⟨a, h⟩, ⟨b, _⟩ => ⟨(a * b) % n, mlt h⟩
 
+/-- Subtraction modulo `n` -/
 protected def sub : Fin n → Fin n → Fin n
   | ⟨a, h⟩, ⟨b, _⟩ => ⟨(a + (n - b)) % n, mlt h⟩
 
@@ -106,6 +130,8 @@ instance instOfNat : OfNat (Fin (no_index (n+1))) i where
 instance : Inhabited (Fin (no_index (n+1))) where
   default := 0
 
+@[simp] theorem zero_eta : (⟨0, Nat.zero_lt_succ _⟩ : Fin (n + 1)) = 0 := rfl
+
 theorem val_ne_of_ne {i j : Fin n} (h : i ≠ j) : val i ≠ val j :=
   fun h' => absurd (eq_of_val_eq h') h
 
@@ -115,10 +141,56 @@ theorem modn_lt : ∀ {m : Nat} (i : Fin n), m > 0 → (modn i m).val < m
 theorem val_lt_of_le (i : Fin b) (h : b ≤ n) : i.val < n :=
   Nat.lt_of_lt_of_le i.isLt h
 
+protected theorem pos (i : Fin n) : 0 < n :=
+  Nat.lt_of_le_of_lt (Nat.zero_le _) i.2
+
+/-- The greatest value of `Fin (n+1)`. -/
+@[inline] def last (n : Nat) : Fin (n + 1) := ⟨n, n.lt_succ_self⟩
+
+/-- `castLT i h` embeds `i` into a `Fin` where `h` proves it belongs into.  -/
+@[inline] def castLT (i : Fin m) (h : i.1 < n) : Fin n := ⟨i.1, h⟩
+
+/-- `castLE h i` embeds `i` into a larger `Fin` type.  -/
+@[inline] def castLE (h : n ≤ m) (i : Fin n) : Fin m := ⟨i, Nat.lt_of_lt_of_le i.2 h⟩
+
+/-- `cast eq i` embeds `i` into an equal `Fin` type. -/
+@[inline] def cast (eq : n = m) (i : Fin n) : Fin m := ⟨i, eq ▸ i.2⟩
+
+/-- `castAdd m i` embeds `i : Fin n` in `Fin (n+m)`. See also `Fin.natAdd` and `Fin.addNat`. -/
+@[inline] def castAdd (m) : Fin n → Fin (n + m) :=
+  castLE <| Nat.le_add_right n m
+
+/-- `castSucc i` embeds `i : Fin n` in `Fin (n+1)`. -/
+@[inline] def castSucc : Fin n → Fin (n + 1) := castAdd 1
+
+/-- `addNat m i` adds `m` to `i`, generalizes `Fin.succ`. -/
+def addNat (i : Fin n) (m) : Fin (n + m) := ⟨i + m, Nat.add_lt_add_right i.2 _⟩
+
+/-- `natAdd n i` adds `n` to `i` "on the left". -/
+def natAdd (n) (i : Fin m) : Fin (n + m) := ⟨n + i, Nat.add_lt_add_left i.2 _⟩
+
+/-- Maps `0` to `n-1`, `1` to `n-2`, ..., `n-1` to `0`. -/
+@[inline] def rev (i : Fin n) : Fin n := ⟨n - (i + 1), Nat.sub_lt i.pos (Nat.succ_pos _)⟩
+
+/-- `subNat i h` subtracts `m` from `i`, generalizes `Fin.pred`. -/
+@[inline] def subNat (m) (i : Fin (n + m)) (h : m ≤ i) : Fin n :=
+  ⟨i - m, Nat.sub_lt_right_of_lt_add h i.2⟩
+
+/-- Predecessor of a nonzero element of `Fin (n+1)`. -/
+@[inline] def pred {n : Nat} (i : Fin (n + 1)) (h : i ≠ 0) : Fin n :=
+  subNat 1 i <| Nat.pos_of_ne_zero <| mt (Fin.eq_of_val_eq (j := 0)) h
+
+theorem val_inj {a b : Fin n} : a.1 = b.1 ↔ a = b := ⟨Fin.eq_of_val_eq, Fin.val_eq_of_eq⟩
+
+theorem val_congr {n : Nat} {a b : Fin n} (h : a = b) : (a : Nat) = (b : Nat) :=
+  Fin.val_inj.mpr h
+
+theorem val_le_of_le {n : Nat} {a b : Fin n} (h : a ≤ b) : (a : Nat) ≤ (b : Nat) := h
+
+theorem val_le_of_ge {n : Nat} {a b : Fin n} (h : a ≥ b) : (b : Nat) ≤ (a : Nat) := h
+
+theorem val_add_one_le_of_lt {n : Nat} {a b : Fin n} (h : a < b) : (a : Nat) + 1 ≤ (b : Nat) := h
+
+theorem val_add_one_le_of_gt {n : Nat} {a b : Fin n} (h : a > b) : (b : Nat) + 1 ≤ (a : Nat) := h
+
 end Fin
-
-instance [GetElem cont Nat elem dom] : GetElem cont (Fin n) elem fun xs i => dom xs i where
-  getElem xs i h := getElem xs i.1 h
-
-macro_rules
-  | `(tactic| get_elem_tactic_trivial) => `(tactic| apply Fin.val_lt_of_le; get_elem_tactic_trivial; done)

src/Init/Data/Fin/Fold.lean

@@ -0,0 +1,21 @@
+/-
+Copyright (c) 2023 François G. Dorais. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: François G. Dorais
+-/
+prelude
+import Init.Data.Nat.Linear
+
+/-- Folds over `Fin n` from the left: `foldl 3 f x = f (f (f x 0) 1) 2`. -/
+@[inline] def foldl (n) (f : α → Fin n → α) (init : α) : α := loop init 0 where
+  /-- Inner loop for `Fin.foldl`. `Fin.foldl.loop n f x i = f (f (f x i) ...) (n-1)`  -/
+  loop (x : α) (i : Nat) : α :=
+    if h : i < n then loop (f x ⟨i, h⟩) (i+1) else x
+  termination_by n - i
+
+/-- Folds over `Fin n` from the right: `foldr 3 f x = f 0 (f 1 (f 2 x))`. -/
+@[inline] def foldr (n) (f : Fin n → α → α) (init : α) : α := loop ⟨n, Nat.le_refl n⟩ init where
+  /-- Inner loop for `Fin.foldr`. `Fin.foldr.loop n f i x = f 0 (f ... (f (i-1) x))`  -/
+  loop : {i // i ≤ n} → α → α
+  | ⟨0, _⟩, x => x
+  | ⟨i+1, h⟩, x => loop ⟨i, Nat.le_of_lt h⟩ (f ⟨i, h⟩ x)

src/Init/Data/Fin/Iterate.lean

@@ -0,0 +1,95 @@
+/-
+Copyright (c) 2024 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Joe Hendrix
+-/
+prelude
+import Init.PropLemmas
+import Init.Data.Fin.Basic
+
+namespace Fin
+
+/--
+`hIterateFrom f i bnd a` applies `f` over indices `[i:n]` to compute `P n`
+from `P i`.
+
+See `hIterate` below for more details.
+-/
+def hIterateFrom (P : Nat → Sort _) {n} (f : ∀(i : Fin n), P i.val → P (i.val+1))
+      (i : Nat) (ubnd : i ≤ n) (a : P i) : P n :=
+  if g : i < n then
+    hIterateFrom P f (i+1) g (f ⟨i, g⟩ a)
+  else
+    have p : i = n := (or_iff_left g).mp (Nat.eq_or_lt_of_le ubnd)
+    _root_.cast (congrArg P p) a
+  termination_by n - i
+
+/--
+`hIterate` is a heterogenous iterative operation that applies a
+index-dependent function `f` to a value `init : P start` a total of
+`stop - start` times to produce a value of type `P stop`.
+
+Concretely, `hIterate start stop f init` is equal to
+```lean
+  init |> f start _ |> f (start+1) _ ... |> f (end-1) _
+```
+
+Because it is heterogenous and must return a value of type `P stop`,
+`hIterate` requires proof that `start ≤ stop`.
+
+One can prove properties of `hIterate` using the general theorem
+`hIterate_elim` or other more specialized theorems.
+ -/
+def hIterate (P : Nat → Sort _) {n : Nat} (init : P 0) (f : ∀(i : Fin n), P i.val → P (i.val+1)) :
+    P n :=
+  hIterateFrom P f 0 (Nat.zero_le n) init
+
+private theorem hIterateFrom_elim {P : Nat → Sort _}(Q : ∀(i : Nat), P i → Prop)
+    {n  : Nat}
+    (f : ∀(i : Fin n), P i.val → P (i.val+1))
+    {i : Nat} (ubnd : i ≤ n)
+    (s : P i)
+    (init : Q i s)
+    (step : ∀(k : Fin n) (s : P k.val), Q k.val s → Q (k.val+1) (f k s)) :
+    Q n (hIterateFrom P f i ubnd s) := by
+  let ⟨j, p⟩ := Nat.le.dest ubnd
+  induction j generalizing i ubnd init with
+  | zero =>
+    unfold hIterateFrom
+    have g : ¬ (i < n) := by simp at p; simp [p]
+    have r : Q n (_root_.cast (congrArg P p) s) :=
+      @Eq.rec Nat i (fun k eq => Q k (_root_.cast (congrArg P eq) s)) init n p
+    simp only [g, r, dite_false]
+  | succ j inv =>
+    unfold hIterateFrom
+    have d : Nat.succ i + j = n := by simp [Nat.succ_add]; exact p
+    have g : i < n := Nat.le.intro d
+    simp only [g]
+    exact inv _ _ (step ⟨i,g⟩ s init) d
+
+/-
+`hIterate_elim` provides a mechanism for showing that the result of
+`hIterate` satisifies a property `Q stop` by showing that the states
+at the intermediate indices `i : start ≤ i < stop` satisfy `Q i`.
+-/
+theorem hIterate_elim {P : Nat → Sort _} (Q : ∀(i : Nat), P i → Prop)
+    {n : Nat} (f : ∀(i : Fin n), P i.val → P (i.val+1)) (s : P 0) (init : Q 0 s)
+    (step : ∀(k : Fin n) (s : P k.val), Q k.val s → Q (k.val+1) (f k s)) :
+    Q n (hIterate P s f) := by
+  exact hIterateFrom_elim _ _ _ _ init step
+
+/-
+`hIterate_eq`provides a mechanism for replacing `hIterate P s f` with a
+function `state` showing that matches the steps performed by `hIterate`.
+
+This allows rewriting incremental code using `hIterate` with a
+non-incremental state function.
+-/
+theorem hIterate_eq {P : Nat → Sort _} (state : ∀(i : Nat), P i)
+    {n : Nat} (f : ∀(i : Fin n), P i.val → P (i.val+1)) (s : P 0)
+    (init : s = state 0)
+    (step : ∀(i : Fin n), f i (state i) = state (i+1)) :
+    hIterate P s f = state n := by
+  apply hIterate_elim (fun i s => s = state i) f s init
+  intro i s s_eq
+  simp only [s_eq, step]

src/Init/Data/Fin/Lemmas.lean

@@ -0,0 +1,835 @@
+/-
+Copyright (c) 2022 Mario Carneiro. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Mario Carneiro
+-/
+prelude
+import Init.Data.Fin.Basic
+import Init.Data.Nat.Lemmas
+import Init.Ext
+import Init.ByCases
+import Init.Conv
+import Init.Omega
+
+namespace Fin
+
+/-- If you actually have an element of `Fin n`, then the `n` is always positive -/
+theorem size_pos (i : Fin n) : 0 < n := Nat.lt_of_le_of_lt (Nat.zero_le _) i.2
+
+theorem mod_def (a m : Fin n) : a % m = Fin.mk (a % m) (Nat.lt_of_le_of_lt (Nat.mod_le _ _) a.2) :=
+  rfl
+
+theorem mul_def (a b : Fin n) : a * b = Fin.mk ((a * b) % n) (Nat.mod_lt _ a.size_pos) := rfl
+
+theorem sub_def (a b : Fin n) : a - b = Fin.mk ((a + (n - b)) % n) (Nat.mod_lt _ a.size_pos) := rfl
+
+theorem size_pos' : ∀ [Nonempty (Fin n)], 0 < n | ⟨i⟩ => i.size_pos
+
+@[simp] theorem is_lt (a : Fin n) : (a : Nat) < n := a.2
+
+theorem pos_iff_nonempty {n : Nat} : 0 < n ↔ Nonempty (Fin n) :=
+  ⟨fun h => ⟨⟨0, h⟩⟩, fun ⟨i⟩ => i.pos⟩
+
+/-! ### coercions and constructions -/
+
+@[simp] protected theorem eta (a : Fin n) (h : a < n) : (⟨a, h⟩ : Fin n) = a := rfl
+
+@[ext] theorem ext {a b : Fin n} (h : (a : Nat) = b) : a = b := eq_of_val_eq h
+
+theorem ext_iff {a b : Fin n} : a = b ↔ a.1 = b.1 := val_inj.symm
+
+theorem val_ne_iff {a b : Fin n} : a.1 ≠ b.1 ↔ a ≠ b := not_congr val_inj
+
+theorem exists_iff {p : Fin n → Prop} : (∃ i, p i) ↔ ∃ i h, p ⟨i, h⟩ :=
+  ⟨fun ⟨⟨i, hi⟩, hpi⟩ => ⟨i, hi, hpi⟩, fun ⟨i, hi, hpi⟩ => ⟨⟨i, hi⟩, hpi⟩⟩
+
+theorem forall_iff {p : Fin n → Prop} : (∀ i, p i) ↔ ∀ i h, p ⟨i, h⟩ :=
+  ⟨fun h i hi => h ⟨i, hi⟩, fun h ⟨i, hi⟩ => h i hi⟩
+
+protected theorem mk.inj_iff {n a b : Nat} {ha : a < n} {hb : b < n} :
+    (⟨a, ha⟩ : Fin n) = ⟨b, hb⟩ ↔ a = b := ext_iff
+
+theorem val_mk {m n : Nat} (h : m < n) : (⟨m, h⟩ : Fin n).val = m := rfl
+
+theorem eq_mk_iff_val_eq {a : Fin n} {k : Nat} {hk : k < n} :
+    a = ⟨k, hk⟩ ↔ (a : Nat) = k := ext_iff
+
+theorem mk_val (i : Fin n) : (⟨i, i.isLt⟩ : Fin n) = i := Fin.eta ..
+
+@[simp] theorem val_ofNat' (a : Nat) (is_pos : n > 0) :
+  (Fin.ofNat' a is_pos).val = a % n := rfl
+
+@[deprecated ofNat'_zero_val] theorem ofNat'_zero_val : (Fin.ofNat' 0 h).val = 0 := Nat.zero_mod _
+
+@[simp] theorem mod_val (a b : Fin n) : (a % b).val = a.val % b.val :=
+  rfl
+
+@[simp] theorem div_val (a b : Fin n) : (a / b).val = a.val / b.val :=
+  rfl
+
+@[simp] theorem modn_val (a : Fin n) (b : Nat) : (a.modn b).val = a.val % b :=
+  rfl
+
+theorem ite_val {n : Nat} {c : Prop} [Decidable c] {x : c → Fin n} (y : ¬c → Fin n) :
+    (if h : c then x h else y h).val = if h : c then (x h).val else (y h).val := by
+  by_cases c <;> simp [*]
+
+theorem dite_val {n : Nat} {c : Prop} [Decidable c] {x y : Fin n} :
+    (if c then x else y).val = if c then x.val else y.val := by
+  by_cases c <;> simp [*]
+
+/-! ### order -/
+
+theorem le_def {a b : Fin n} : a ≤ b ↔ a.1 ≤ b.1 := .rfl
+
+theorem lt_def {a b : Fin n} : a < b ↔ a.1 < b.1 := .rfl
+
+theorem lt_iff_val_lt_val {a b : Fin n} : a < b ↔ a.val < b.val := Iff.rfl
+
+@[simp] protected theorem not_le {a b : Fin n} : ¬ a ≤ b ↔ b < a := Nat.not_le
+
+@[simp] protected theorem not_lt {a b : Fin n} : ¬ a < b ↔ b ≤ a := Nat.not_lt
+
+protected theorem ne_of_lt {a b : Fin n} (h : a < b) : a ≠ b := Fin.ne_of_val_ne (Nat.ne_of_lt h)
+
+protected theorem ne_of_gt {a b : Fin n} (h : a < b) : b ≠ a := Fin.ne_of_val_ne (Nat.ne_of_gt h)
+
+protected theorem le_of_lt {a b : Fin n} (h : a < b) : a ≤ b := Nat.le_of_lt h
+
+theorem is_le (i : Fin (n + 1)) : i ≤ n := Nat.le_of_lt_succ i.is_lt
+
+@[simp] theorem is_le' {a : Fin n} : a ≤ n := Nat.le_of_lt a.is_lt
+
+theorem mk_lt_of_lt_val {b : Fin n} {a : Nat} (h : a < b) :
+    (⟨a, Nat.lt_trans h b.is_lt⟩ : Fin n) < b := h
+
+theorem mk_le_of_le_val {b : Fin n} {a : Nat} (h : a ≤ b) :
+    (⟨a, Nat.lt_of_le_of_lt h b.is_lt⟩ : Fin n) ≤ b := h
+
+@[simp] theorem mk_le_mk {x y : Nat} {hx hy} : (⟨x, hx⟩ : Fin n) ≤ ⟨y, hy⟩ ↔ x ≤ y := .rfl
+
+@[simp] theorem mk_lt_mk {x y : Nat} {hx hy} : (⟨x, hx⟩ : Fin n) < ⟨y, hy⟩ ↔ x < y := .rfl
+
+@[simp] theorem val_zero (n : Nat) : (0 : Fin (n + 1)).1 = 0 := rfl
+
+@[simp] theorem mk_zero : (⟨0, Nat.succ_pos n⟩ : Fin (n + 1)) = 0 := rfl
+
+@[simp] theorem zero_le (a : Fin (n + 1)) : 0 ≤ a := Nat.zero_le a.val
+
+theorem zero_lt_one : (0 : Fin (n + 2)) < 1 := Nat.zero_lt_one
+
+@[simp] theorem not_lt_zero (a : Fin (n + 1)) : ¬a < 0 := nofun
+
+theorem pos_iff_ne_zero {a : Fin (n + 1)} : 0 < a ↔ a ≠ 0 := by
+  rw [lt_def, val_zero, Nat.pos_iff_ne_zero, ← val_ne_iff]; rfl
+
+theorem eq_zero_or_eq_succ {n : Nat} : ∀ i : Fin (n + 1), i = 0 ∨ ∃ j : Fin n, i = j.succ
+  | 0 => .inl rfl
+  | ⟨j + 1, h⟩ => .inr ⟨⟨j, Nat.lt_of_succ_lt_succ h⟩, rfl⟩
+
+theorem eq_succ_of_ne_zero {n : Nat} {i : Fin (n + 1)} (hi : i ≠ 0) : ∃ j : Fin n, i = j.succ :=
+  (eq_zero_or_eq_succ i).resolve_left hi
+
+@[simp] theorem val_rev (i : Fin n) : rev i = n - (i + 1) := rfl
+
+@[simp] theorem rev_rev (i : Fin n) : rev (rev i) = i := ext <| by
+  rw [val_rev, val_rev, ← Nat.sub_sub, Nat.sub_sub_self (by exact i.2), Nat.add_sub_cancel]
+
+@[simp] theorem rev_le_rev {i j : Fin n} : rev i ≤ rev j ↔ j ≤ i := by
+  simp only [le_def, val_rev, Nat.sub_le_sub_iff_left (Nat.succ_le.2 j.is_lt)]
+  exact Nat.succ_le_succ_iff
+
+@[simp] theorem rev_inj {i j : Fin n} : rev i = rev j ↔ i = j :=
+  ⟨fun h => by simpa using congrArg rev h, congrArg _⟩
+
+theorem rev_eq {n a : Nat} (i : Fin (n + 1)) (h : n = a + i) :
+    rev i = ⟨a, Nat.lt_succ_of_le (h ▸ Nat.le_add_right ..)⟩ := by
+  ext; dsimp
+  conv => lhs; congr; rw [h]
+  rw [Nat.add_assoc, Nat.add_sub_cancel]
+
+@[simp] theorem rev_lt_rev {i j : Fin n} : rev i < rev j ↔ j < i := by
+  rw [← Fin.not_le, ← Fin.not_le, rev_le_rev]
+
+@[simp] theorem val_last (n : Nat) : last n = n := rfl
+
+theorem le_last (i : Fin (n + 1)) : i ≤ last n := Nat.le_of_lt_succ i.is_lt
+
+theorem last_pos : (0 : Fin (n + 2)) < last (n + 1) := Nat.succ_pos _
+
+theorem eq_last_of_not_lt {i : Fin (n + 1)} (h : ¬(i : Nat) < n) : i = last n :=
+  ext <| Nat.le_antisymm (le_last i) (Nat.not_lt.1 h)
+
+theorem val_lt_last {i : Fin (n + 1)} : i ≠ last n → (i : Nat) < n :=
+  Decidable.not_imp_comm.1 eq_last_of_not_lt
+
+@[simp] theorem rev_last (n : Nat) : rev (last n) = 0 := ext <| by simp
+
+@[simp] theorem rev_zero (n : Nat) : rev 0 = last n := by
+  rw [← rev_rev (last _), rev_last]
+
+/-! ### addition, numerals, and coercion from Nat -/
+
+@[simp] theorem val_one (n : Nat) : (1 : Fin (n + 2)).val = 1 := rfl
+
+@[simp] theorem mk_one : (⟨1, Nat.succ_lt_succ (Nat.succ_pos n)⟩ : Fin (n + 2)) = (1 : Fin _) := rfl
+
+theorem subsingleton_iff_le_one : Subsingleton (Fin n) ↔ n ≤ 1 := by
+  (match n with | 0 | 1 | n+2 => ?_) <;> try simp
+  · exact ⟨nofun⟩
+  · exact ⟨fun ⟨0, _⟩ ⟨0, _⟩ => rfl⟩
+  · exact iff_of_false (fun h => Fin.ne_of_lt zero_lt_one (h.elim ..)) (of_decide_eq_false rfl)
+
+instance subsingleton_zero : Subsingleton (Fin 0) := subsingleton_iff_le_one.2 (by decide)
+
+instance subsingleton_one : Subsingleton (Fin 1) := subsingleton_iff_le_one.2 (by decide)
+
+theorem fin_one_eq_zero (a : Fin 1) : a = 0 := Subsingleton.elim a 0
+
+theorem add_def (a b : Fin n) : a + b = Fin.mk ((a + b) % n) (Nat.mod_lt _ a.size_pos) := rfl
+
+theorem val_add (a b : Fin n) : (a + b).val = (a.val + b.val) % n := rfl
+
+theorem val_add_one_of_lt {n : Nat} {i : Fin n.succ} (h : i < last _) : (i + 1).1 = i + 1 := by
+  match n with
+  | 0 => cases h
+  | n+1 => rw [val_add, val_one, Nat.mod_eq_of_lt (by exact Nat.succ_lt_succ h)]
+
+@[simp] theorem last_add_one : ∀ n, last n + 1 = 0
+  | 0 => rfl
+  | n + 1 => by ext; rw [val_add, val_zero, val_last, val_one, Nat.mod_self]
+
+theorem val_add_one {n : Nat} (i : Fin (n + 1)) :
+    ((i + 1 : Fin (n + 1)) : Nat) = if i = last _ then (0 : Nat) else i + 1 := by
+  match Nat.eq_or_lt_of_le (le_last i) with
+  | .inl h => cases Fin.eq_of_val_eq h; simp
+  | .inr h => simpa [Fin.ne_of_lt h] using val_add_one_of_lt h
+
+@[simp] theorem val_two {n : Nat} : (2 : Fin (n + 3)).val = 2 := rfl
+
+theorem add_one_pos (i : Fin (n + 1)) (h : i < Fin.last n) : (0 : Fin (n + 1)) < i + 1 := by
+  match n with
+  | 0 => cases h
+  | n+1 =>
+    rw [Fin.lt_def, val_last, ← Nat.add_lt_add_iff_right] at h
+    rw [Fin.lt_def, val_add, val_zero, val_one, Nat.mod_eq_of_lt h]
+    exact Nat.zero_lt_succ _
+
+theorem one_pos : (0 : Fin (n + 2)) < 1 := Nat.succ_pos 0
+
+theorem zero_ne_one : (0 : Fin (n + 2)) ≠ 1 := Fin.ne_of_lt one_pos
+
+/-! ### succ and casts into larger Fin types -/
+
+@[simp] theorem val_succ (j : Fin n) : (j.succ : Nat) = j + 1 := rfl
+
+@[simp] theorem succ_pos (a : Fin n) : (0 : Fin (n + 1)) < a.succ := by
+  simp [Fin.lt_def, Nat.succ_pos]
+
+@[simp] theorem succ_le_succ_iff {a b : Fin n} : a.succ ≤ b.succ ↔ a ≤ b := Nat.succ_le_succ_iff
+
+@[simp] theorem succ_lt_succ_iff {a b : Fin n} : a.succ < b.succ ↔ a < b := Nat.succ_lt_succ_iff
+
+@[simp] theorem succ_inj {a b : Fin n} : a.succ = b.succ ↔ a = b := by
+  refine ⟨fun h => ext ?_, congrArg _⟩
+  apply Nat.le_antisymm <;> exact succ_le_succ_iff.1 (h ▸ Nat.le_refl _)
+
+theorem succ_ne_zero {n} : ∀ k : Fin n, Fin.succ k ≠ 0
+  | ⟨k, _⟩, heq => Nat.succ_ne_zero k <| ext_iff.1 heq
+
+@[simp] theorem succ_zero_eq_one : Fin.succ (0 : Fin (n + 1)) = 1 := rfl
+
+/-- Version of `succ_one_eq_two` to be used by `dsimp` -/
+@[simp] theorem succ_one_eq_two : Fin.succ (1 : Fin (n + 2)) = 2 := rfl
+
+@[simp] theorem succ_mk (n i : Nat) (h : i < n) :
+    Fin.succ ⟨i, h⟩ = ⟨i + 1, Nat.succ_lt_succ h⟩ := rfl
+
+theorem mk_succ_pos (i : Nat) (h : i < n) :
+    (0 : Fin (n + 1)) < ⟨i.succ, Nat.add_lt_add_right h 1⟩ := by
+  rw [lt_def, val_zero]; exact Nat.succ_pos i
+
+theorem one_lt_succ_succ (a : Fin n) : (1 : Fin (n + 2)) < a.succ.succ := by
+  let n+1 := n
+  rw [← succ_zero_eq_one, succ_lt_succ_iff]; exact succ_pos a
+
+@[simp] theorem add_one_lt_iff {n : Nat} {k : Fin (n + 2)} : k + 1 < k ↔ k = last _ := by
+  simp only [lt_def, val_add, val_last, ext_iff]
+  let ⟨k, hk⟩ := k
+  match Nat.eq_or_lt_of_le (Nat.le_of_lt_succ hk) with
+  | .inl h => cases h; simp [Nat.succ_pos]
+  | .inr hk' => simp [Nat.ne_of_lt hk', Nat.mod_eq_of_lt (Nat.succ_lt_succ hk'), Nat.le_succ]
+
+@[simp] theorem add_one_le_iff {n : Nat} : ∀ {k : Fin (n + 1)}, k + 1 ≤ k ↔ k = last _ := by
+  match n with
+  | 0 =>
+    intro (k : Fin 1)
+    exact iff_of_true (Subsingleton.elim (α := Fin 1) (k+1) _ ▸ Nat.le_refl _) (fin_one_eq_zero ..)
+  | n + 1 =>
+    intro (k : Fin (n+2))
+    rw [← add_one_lt_iff, lt_def, le_def, Nat.lt_iff_le_and_ne, and_iff_left]
+    rw [val_add_one]
+    split <;> simp [*, (Nat.succ_ne_zero _).symm, Nat.ne_of_gt (Nat.lt_succ_self _)]
+
+@[simp] theorem last_le_iff {n : Nat} {k : Fin (n + 1)} : last n ≤ k ↔ k = last n := by
+  rw [ext_iff, Nat.le_antisymm_iff, le_def, and_iff_right (by apply le_last)]
+
+@[simp] theorem lt_add_one_iff {n : Nat} {k : Fin (n + 1)} : k < k + 1 ↔ k < last n := by
+  rw [← Decidable.not_iff_not]; simp
+
+@[simp] theorem le_zero_iff {n : Nat} {k : Fin (n + 1)} : k ≤ 0 ↔ k = 0 :=
+  ⟨fun h => Fin.eq_of_val_eq <| Nat.eq_zero_of_le_zero h, (· ▸ Nat.le_refl _)⟩
+
+theorem succ_succ_ne_one (a : Fin n) : Fin.succ (Fin.succ a) ≠ 1 :=
+  Fin.ne_of_gt (one_lt_succ_succ a)
+
+@[simp] theorem coe_castLT (i : Fin m) (h : i.1 < n) : (castLT i h : Nat) = i := rfl
+
+@[simp] theorem castLT_mk (i n m : Nat) (hn : i < n) (hm : i < m) : castLT ⟨i, hn⟩ hm = ⟨i, hm⟩ :=
+  rfl
+
+@[simp] theorem coe_castLE (h : n ≤ m) (i : Fin n) : (castLE h i : Nat) = i := rfl
+
+@[simp] theorem castLE_mk (i n m : Nat) (hn : i < n) (h : n ≤ m) :
+    castLE h ⟨i, hn⟩ = ⟨i, Nat.lt_of_lt_of_le hn h⟩ := rfl
+
+@[simp] theorem castLE_zero {n m : Nat} (h : n.succ ≤ m.succ) : castLE h 0 = 0 := by simp [ext_iff]
+
+@[simp] theorem castLE_succ {m n : Nat} (h : m + 1 ≤ n + 1) (i : Fin m) :
+    castLE h i.succ = (castLE (Nat.succ_le_succ_iff.mp h) i).succ := by simp [ext_iff]
+
+@[simp] theorem castLE_castLE {k m n} (km : k ≤ m) (mn : m ≤ n) (i : Fin k) :
+    Fin.castLE mn (Fin.castLE km i) = Fin.castLE (Nat.le_trans km mn) i :=
+  Fin.ext (by simp only [coe_castLE])
+
+@[simp] theorem castLE_comp_castLE {k m n} (km : k ≤ m) (mn : m ≤ n) :
+    Fin.castLE mn ∘ Fin.castLE km = Fin.castLE (Nat.le_trans km mn) :=
+  funext (castLE_castLE km mn)
+
+@[simp] theorem coe_cast (h : n = m) (i : Fin n) : (cast h i : Nat) = i := rfl
+
+@[simp] theorem cast_last {n' : Nat} {h : n + 1 = n' + 1} : cast h (last n) = last n' :=
+  ext (by rw [coe_cast, val_last, val_last, Nat.succ.inj h])
+
+@[simp] theorem cast_mk (h : n = m) (i : Nat) (hn : i < n) : cast h ⟨i, hn⟩ = ⟨i, h ▸ hn⟩ := rfl
+
+@[simp] theorem cast_trans {k : Nat} (h : n = m) (h' : m = k) {i : Fin n} :
+    cast h' (cast h i) = cast (Eq.trans h h') i := rfl
+
+theorem castLE_of_eq {m n : Nat} (h : m = n) {h' : m ≤ n} : castLE h' = Fin.cast h := rfl
+
+@[simp] theorem coe_castAdd (m : Nat) (i : Fin n) : (castAdd m i : Nat) = i := rfl
+
+@[simp] theorem castAdd_zero : (castAdd 0 : Fin n → Fin (n + 0)) = cast rfl := rfl
+
+theorem castAdd_lt {m : Nat} (n : Nat) (i : Fin m) : (castAdd n i : Nat) < m := by simp
+
+@[simp] theorem castAdd_mk (m : Nat) (i : Nat) (h : i < n) :
+    castAdd m ⟨i, h⟩ = ⟨i, Nat.lt_add_right m h⟩ := rfl
+
+@[simp] theorem castAdd_castLT (m : Nat) (i : Fin (n + m)) (hi : i.val < n) :
+    castAdd m (castLT i hi) = i := rfl
+
+@[simp] theorem castLT_castAdd (m : Nat) (i : Fin n) :
+    castLT (castAdd m i) (castAdd_lt m i) = i := rfl
+
+/-- For rewriting in the reverse direction, see `Fin.cast_castAdd_left`. -/
+theorem castAdd_cast {n n' : Nat} (m : Nat) (i : Fin n') (h : n' = n) :
+    castAdd m (Fin.cast h i) = Fin.cast (congrArg (. + m) h) (castAdd m i) := ext rfl
+
+theorem cast_castAdd_left {n n' m : Nat} (i : Fin n') (h : n' + m = n + m) :
+    cast h (castAdd m i) = castAdd m (cast (Nat.add_right_cancel h) i) := rfl
+
+@[simp] theorem cast_castAdd_right {n m m' : Nat} (i : Fin n) (h : n + m' = n + m) :
+    cast h (castAdd m' i) = castAdd m i := rfl
+
+theorem castAdd_castAdd {m n p : Nat} (i : Fin m) :
+    castAdd p (castAdd n i) = cast (Nat.add_assoc ..).symm (castAdd (n + p) i) := rfl
+
+/-- The cast of the successor is the successor of the cast. See `Fin.succ_cast_eq` for rewriting in
+the reverse direction. -/
+@[simp] theorem cast_succ_eq {n' : Nat} (i : Fin n) (h : n.succ = n'.succ) :
+    cast h i.succ = (cast (Nat.succ.inj h) i).succ := rfl
+
+theorem succ_cast_eq {n' : Nat} (i : Fin n) (h : n = n') :
+    (cast h i).succ = cast (by rw [h]) i.succ := rfl
+
+@[simp] theorem coe_castSucc (i : Fin n) : (Fin.castSucc i : Nat) = i := rfl
+
+@[simp] theorem castSucc_mk (n i : Nat) (h : i < n) : castSucc ⟨i, h⟩ = ⟨i, Nat.lt.step h⟩ := rfl
+
+@[simp] theorem cast_castSucc {n' : Nat} {h : n + 1 = n' + 1} {i : Fin n} :
+    cast h (castSucc i) = castSucc (cast (Nat.succ.inj h) i) := rfl
+
+theorem castSucc_lt_succ (i : Fin n) : Fin.castSucc i < i.succ :=
+  lt_def.2 <| by simp only [coe_castSucc, val_succ, Nat.lt_succ_self]
+
+theorem le_castSucc_iff {i : Fin (n + 1)} {j : Fin n} : i ≤ Fin.castSucc j ↔ i < j.succ := by
+  simpa [lt_def, le_def] using Nat.succ_le_succ_iff.symm
+
+theorem castSucc_lt_iff_succ_le {n : Nat} {i : Fin n} {j : Fin (n + 1)} :
+    Fin.castSucc i < j ↔ i.succ ≤ j := .rfl
+
+@[simp] theorem succ_last (n : Nat) : (last n).succ = last n.succ := rfl
+
+@[simp] theorem succ_eq_last_succ {n : Nat} (i : Fin n.succ) :
+    i.succ = last (n + 1) ↔ i = last n := by rw [← succ_last, succ_inj]
+
+@[simp] theorem castSucc_castLT (i : Fin (n + 1)) (h : (i : Nat) < n) :
+    castSucc (castLT i h) = i := rfl
+
+@[simp] theorem castLT_castSucc {n : Nat} (a : Fin n) (h : (a : Nat) < n) :
+    castLT (castSucc a) h = a := rfl
+
+@[simp] theorem castSucc_lt_castSucc_iff {a b : Fin n} :
+    Fin.castSucc a < Fin.castSucc b ↔ a < b := .rfl
+
+theorem castSucc_inj {a b : Fin n} : castSucc a = castSucc b ↔ a = b := by simp [ext_iff]
+
+theorem castSucc_lt_last (a : Fin n) : castSucc a < last n := a.is_lt
+
+@[simp] theorem castSucc_zero : castSucc (0 : Fin (n + 1)) = 0 := rfl
+
+@[simp] theorem castSucc_one {n : Nat} : castSucc (1 : Fin (n + 2)) = 1 := rfl
+
+/-- `castSucc i` is positive when `i` is positive -/
+theorem castSucc_pos {i : Fin (n + 1)} (h : 0 < i) : 0 < castSucc i := by
+  simpa [lt_def] using h
+
+@[simp] theorem castSucc_eq_zero_iff (a : Fin (n + 1)) : castSucc a = 0 ↔ a = 0 := by simp [ext_iff]
+
+theorem castSucc_ne_zero_iff (a : Fin (n + 1)) : castSucc a ≠ 0 ↔ a ≠ 0 :=
+  not_congr <| castSucc_eq_zero_iff a
+
+theorem castSucc_fin_succ (n : Nat) (j : Fin n) :
+    castSucc (Fin.succ j) = Fin.succ (castSucc j) := by simp [Fin.ext_iff]
+
+@[simp]
+theorem coeSucc_eq_succ {a : Fin n} : castSucc a + 1 = a.succ := by
+  cases n
+  · exact a.elim0
+  · simp [ext_iff, add_def, Nat.mod_eq_of_lt (Nat.succ_lt_succ a.is_lt)]
+
+theorem lt_succ {a : Fin n} : castSucc a < a.succ := by
+  rw [castSucc, lt_def, coe_castAdd, val_succ]; exact Nat.lt_succ_self a.val
+
+theorem exists_castSucc_eq {n : Nat} {i : Fin (n + 1)} : (∃ j, castSucc j = i) ↔ i ≠ last n :=
+  ⟨fun ⟨j, hj⟩ => hj ▸ Fin.ne_of_lt j.castSucc_lt_last,
+   fun hi => ⟨i.castLT <| Fin.val_lt_last hi, rfl⟩⟩
+
+theorem succ_castSucc {n : Nat} (i : Fin n) : i.castSucc.succ = castSucc i.succ := rfl
+
+@[simp] theorem coe_addNat (m : Nat) (i : Fin n) : (addNat i m : Nat) = i + m := rfl
+
+@[simp] theorem addNat_one {i : Fin n} : addNat i 1 = i.succ := rfl
+
+theorem le_coe_addNat (m : Nat) (i : Fin n) : m ≤ addNat i m :=
+  Nat.le_add_left _ _
+
+@[simp] theorem addNat_mk (n i : Nat) (hi : i < m) :
+    addNat ⟨i, hi⟩ n = ⟨i + n, Nat.add_lt_add_right hi n⟩ := rfl
+
+@[simp] theorem cast_addNat_zero {n n' : Nat} (i : Fin n) (h : n + 0 = n') :
+    cast h (addNat i 0) = cast ((Nat.add_zero _).symm.trans h) i := rfl
+
+/-- For rewriting in the reverse direction, see `Fin.cast_addNat_left`. -/
+theorem addNat_cast {n n' m : Nat} (i : Fin n') (h : n' = n) :
+    addNat (cast h i) m = cast (congrArg (. + m) h) (addNat i m) := rfl
+
+theorem cast_addNat_left {n n' m : Nat} (i : Fin n') (h : n' + m = n + m) :
+    cast h (addNat i m) = addNat (cast (Nat.add_right_cancel h) i) m := rfl
+
+@[simp] theorem cast_addNat_right {n m m' : Nat} (i : Fin n) (h : n + m' = n + m) :
+    cast h (addNat i m') = addNat i m :=
+  ext <| (congrArg ((· + ·) (i : Nat)) (Nat.add_left_cancel h) : _)
+
+@[simp] theorem coe_natAdd (n : Nat) {m : Nat} (i : Fin m) : (natAdd n i : Nat) = n + i := rfl
+
+@[simp] theorem natAdd_mk (n i : Nat) (hi : i < m) :
+    natAdd n ⟨i, hi⟩ = ⟨n + i, Nat.add_lt_add_left hi n⟩ := rfl
+
+theorem le_coe_natAdd (m : Nat) (i : Fin n) : m ≤ natAdd m i := Nat.le_add_right ..
+
+theorem natAdd_zero {n : Nat} : natAdd 0 = cast (Nat.zero_add n).symm := by ext; simp
+
+/-- For rewriting in the reverse direction, see `Fin.cast_natAdd_right`. -/
+theorem natAdd_cast {n n' : Nat} (m : Nat) (i : Fin n') (h : n' = n) :
+    natAdd m (cast h i) = cast (congrArg _ h) (natAdd m i) := rfl
+
+theorem cast_natAdd_right {n n' m : Nat} (i : Fin n') (h : m + n' = m + n) :
+    cast h (natAdd m i) = natAdd m (cast (Nat.add_left_cancel h) i) := rfl
+
+@[simp] theorem cast_natAdd_left {n m m' : Nat} (i : Fin n) (h : m' + n = m + n) :
+    cast h (natAdd m' i) = natAdd m i :=
+  ext <| (congrArg (· + (i : Nat)) (Nat.add_right_cancel h) : _)
+
+theorem castAdd_natAdd (p m : Nat) {n : Nat} (i : Fin n) :
+    castAdd p (natAdd m i) = cast (Nat.add_assoc ..).symm (natAdd m (castAdd p i)) := rfl
+
+theorem natAdd_castAdd (p m : Nat) {n : Nat} (i : Fin n) :
+    natAdd m (castAdd p i) = cast (Nat.add_assoc ..) (castAdd p (natAdd m i)) := rfl
+
+theorem natAdd_natAdd (m n : Nat) {p : Nat} (i : Fin p) :
+    natAdd m (natAdd n i) = cast (Nat.add_assoc ..) (natAdd (m + n) i) :=
+  ext <| (Nat.add_assoc ..).symm
+
+@[simp]
+theorem cast_natAdd_zero {n n' : Nat} (i : Fin n) (h : 0 + n = n') :
+    cast h (natAdd 0 i) = cast ((Nat.zero_add _).symm.trans h) i :=
+  ext <| Nat.zero_add _
+
+@[simp]
+theorem cast_natAdd (n : Nat) {m : Nat} (i : Fin m) :
+    cast (Nat.add_comm ..) (natAdd n i) = addNat i n := ext <| Nat.add_comm ..
+
+@[simp]
+theorem cast_addNat {n : Nat} (m : Nat) (i : Fin n) :
+    cast (Nat.add_comm ..) (addNat i m) = natAdd m i := ext <| Nat.add_comm ..
+
+@[simp] theorem natAdd_last {m n : Nat} : natAdd n (last m) = last (n + m) := rfl
+
+theorem natAdd_castSucc {m n : Nat} {i : Fin m} : natAdd n (castSucc i) = castSucc (natAdd n i) :=
+  rfl
+
+theorem rev_castAdd (k : Fin n) (m : Nat) : rev (castAdd m k) = addNat (rev k) m := ext <| by
+  rw [val_rev, coe_castAdd, coe_addNat, val_rev, Nat.sub_add_comm (Nat.succ_le_of_lt k.is_lt)]
+
+theorem rev_addNat (k : Fin n) (m : Nat) : rev (addNat k m) = castAdd m (rev k) := by
+  rw [← rev_rev (castAdd ..), rev_castAdd, rev_rev]
+
+theorem rev_castSucc (k : Fin n) : rev (castSucc k) = succ (rev k) := k.rev_castAdd 1
+
+theorem rev_succ (k : Fin n) : rev (succ k) = castSucc (rev k) := k.rev_addNat 1
+
+/-! ### pred -/
+
+@[simp] theorem coe_pred (j : Fin (n + 1)) (h : j ≠ 0) : (j.pred h : Nat) = j - 1 := rfl
+
+@[simp] theorem succ_pred : ∀ (i : Fin (n + 1)) (h : i ≠ 0), (i.pred h).succ = i
+  | ⟨0, h⟩, hi => by simp only [mk_zero, ne_eq, not_true] at hi
+  | ⟨n + 1, h⟩, hi => rfl
+
+@[simp]
+theorem pred_succ (i : Fin n) {h : i.succ ≠ 0} : i.succ.pred h = i := by
+  cases i
+  rfl
+
+theorem pred_eq_iff_eq_succ {n : Nat} (i : Fin (n + 1)) (hi : i ≠ 0) (j : Fin n) :
+    i.pred hi = j ↔ i = j.succ :=
+  ⟨fun h => by simp only [← h, Fin.succ_pred], fun h => by simp only [h, Fin.pred_succ]⟩
+
+theorem pred_mk_succ (i : Nat) (h : i < n + 1) :
+    Fin.pred ⟨i + 1, Nat.add_lt_add_right h 1⟩ (ne_of_val_ne (Nat.ne_of_gt (mk_succ_pos i h))) =
+      ⟨i, h⟩ := by
+  simp only [ext_iff, coe_pred, Nat.add_sub_cancel]
+
+@[simp] theorem pred_mk_succ' (i : Nat) (h₁ : i + 1 < n + 1 + 1) (h₂) :
+    Fin.pred ⟨i + 1, h₁⟩ h₂ = ⟨i, Nat.lt_of_succ_lt_succ h₁⟩ := pred_mk_succ i _
+
+-- This is not a simp theorem by default, because `pred_mk_succ` is nicer when it applies.
+theorem pred_mk {n : Nat} (i : Nat) (h : i < n + 1) (w) : Fin.pred ⟨i, h⟩ w =
+    ⟨i - 1, Nat.sub_lt_right_of_lt_add (Nat.pos_iff_ne_zero.2 (Fin.val_ne_of_ne w)) h⟩ :=
+  rfl
+
+@[simp] theorem pred_le_pred_iff {n : Nat} {a b : Fin n.succ} {ha : a ≠ 0} {hb : b ≠ 0} :
+    a.pred ha ≤ b.pred hb ↔ a ≤ b := by rw [← succ_le_succ_iff, succ_pred, succ_pred]
+
+@[simp] theorem pred_lt_pred_iff {n : Nat} {a b : Fin n.succ} {ha : a ≠ 0} {hb : b ≠ 0} :
+    a.pred ha < b.pred hb ↔ a < b := by rw [← succ_lt_succ_iff, succ_pred, succ_pred]
+
+@[simp] theorem pred_inj :
+    ∀ {a b : Fin (n + 1)} {ha : a ≠ 0} {hb : b ≠ 0}, a.pred ha = b.pred hb ↔ a = b
+  | ⟨0, _⟩, _, ha, _ => by simp only [mk_zero, ne_eq, not_true] at ha
+  | ⟨i + 1, _⟩, ⟨0, _⟩, _, hb => by simp only [mk_zero, ne_eq, not_true] at hb
+  | ⟨i + 1, hi⟩, ⟨j + 1, hj⟩, ha, hb => by simp [ext_iff, Nat.succ.injEq]
+
+@[simp] theorem pred_one {n : Nat} :
+    Fin.pred (1 : Fin (n + 2)) (Ne.symm (Fin.ne_of_lt one_pos)) = 0 := rfl
+
+theorem pred_add_one (i : Fin (n + 2)) (h : (i : Nat) < n + 1) :
+    pred (i + 1) (Fin.ne_of_gt (add_one_pos _ (lt_def.2 h))) = castLT i h := by
+  rw [ext_iff, coe_pred, coe_castLT, val_add, val_one, Nat.mod_eq_of_lt, Nat.add_sub_cancel]
+  exact Nat.add_lt_add_right h 1
+
+@[simp] theorem coe_subNat (i : Fin (n + m)) (h : m ≤ i) : (i.subNat m h : Nat) = i - m := rfl
+
+@[simp] theorem subNat_mk {i : Nat} (h₁ : i < n + m) (h₂ : m ≤ i) :
+    subNat m ⟨i, h₁⟩ h₂ = ⟨i - m, Nat.sub_lt_right_of_lt_add h₂ h₁⟩ := rfl
+
+@[simp] theorem pred_castSucc_succ (i : Fin n) :
+    pred (castSucc i.succ) (Fin.ne_of_gt (castSucc_pos i.succ_pos)) = castSucc i := rfl
+
+@[simp] theorem addNat_subNat {i : Fin (n + m)} (h : m ≤ i) : addNat (subNat m i h) m = i :=
+  ext <| Nat.sub_add_cancel h
+
+@[simp] theorem subNat_addNat (i : Fin n) (m : Nat) (h : m ≤ addNat i m := le_coe_addNat m i) :
+    subNat m (addNat i m) h = i := ext <| Nat.add_sub_cancel i m
+
+@[simp] theorem natAdd_subNat_cast {i : Fin (n + m)} (h : n ≤ i) :
+    natAdd n (subNat n (cast (Nat.add_comm ..) i) h) = i := by simp [← cast_addNat]; rfl
+
+/-! ### recursion and induction principles -/
+
+/-- Define `motive n i` by induction on `i : Fin n` interpreted as `(0 : Fin (n - i)).succ.succ…`.
+This function has two arguments: `zero n` defines `0`-th element `motive (n+1) 0` of an
+`(n+1)`-tuple, and `succ n i` defines `(i+1)`-st element of `(n+1)`-tuple based on `n`, `i`, and
+`i`-th element of `n`-tuple. -/
+-- FIXME: Performance review
+@[elab_as_elim] def succRec {motive : ∀ n, Fin n → Sort _}
+    (zero : ∀ n, motive n.succ (0 : Fin (n + 1)))
+    (succ : ∀ n i, motive n i → motive n.succ i.succ) : ∀ {n : Nat} (i : Fin n), motive n i
+  | 0, i => i.elim0
+  | Nat.succ n, ⟨0, _⟩ => by rw [mk_zero]; exact zero n
+  | Nat.succ _, ⟨Nat.succ i, h⟩ => succ _ _ (succRec zero succ ⟨i, Nat.lt_of_succ_lt_succ h⟩)
+
+/-- Define `motive n i` by induction on `i : Fin n` interpreted as `(0 : Fin (n - i)).succ.succ…`.
+This function has two arguments:
+`zero n` defines the `0`-th element `motive (n+1) 0` of an `(n+1)`-tuple, and
+`succ n i` defines the `(i+1)`-st element of an `(n+1)`-tuple based on `n`, `i`,
+and the `i`-th element of an `n`-tuple.
+
+A version of `Fin.succRec` taking `i : Fin n` as the first argument. -/
+-- FIXME: Performance review
+@[elab_as_elim] def succRecOn {n : Nat} (i : Fin n) {motive : ∀ n, Fin n → Sort _}
+    (zero : ∀ n, motive (n + 1) 0) (succ : ∀ n i, motive n i → motive (Nat.succ n) i.succ) :
+    motive n i := i.succRec zero succ
+
+@[simp] theorem succRecOn_zero {motive : ∀ n, Fin n → Sort _} {zero succ} (n) :
+    @Fin.succRecOn (n + 1) 0 motive zero succ = zero n := by
+  cases n <;> rfl
+
+@[simp] theorem succRecOn_succ {motive : ∀ n, Fin n → Sort _} {zero succ} {n} (i : Fin n) :
+    @Fin.succRecOn (n + 1) i.succ motive zero succ = succ n i (Fin.succRecOn i zero succ) := by
+  cases i; rfl
+
+/-- Define `motive i` by induction on `i : Fin (n + 1)` via induction on the underlying `Nat` value.
+This function has two arguments: `zero` handles the base case on `motive 0`,
+and `succ` defines the inductive step using `motive i.castSucc`.
+-/
+-- FIXME: Performance review
+@[elab_as_elim] def induction {motive : Fin (n + 1) → Sort _} (zero : motive 0)
+    (succ : ∀ i : Fin n, motive (castSucc i) → motive i.succ) :
+    ∀ i : Fin (n + 1), motive i
+  | ⟨0, hi⟩ => by rwa [Fin.mk_zero]
+  | ⟨i+1, hi⟩ => succ ⟨i, Nat.lt_of_succ_lt_succ hi⟩ (induction zero succ ⟨i, Nat.lt_of_succ_lt hi⟩)
+
+@[simp] theorem induction_zero {motive : Fin (n + 1) → Sort _} (zero : motive 0)
+    (hs : ∀ i : Fin n, motive (castSucc i) → motive i.succ) :
+    (induction zero hs : ∀ i : Fin (n + 1), motive i) 0 = zero := rfl
+
+@[simp] theorem induction_succ {motive : Fin (n + 1) → Sort _} (zero : motive 0)
+    (succ : ∀ i : Fin n, motive (castSucc i) → motive i.succ) (i : Fin n) :
+    induction (motive := motive) zero succ i.succ = succ i (induction zero succ (castSucc i)) := rfl
+
+/-- Define `motive i` by induction on `i : Fin (n + 1)` via induction on the underlying `Nat` value.
+This function has two arguments: `zero` handles the base case on `motive 0`,
+and `succ` defines the inductive step using `motive i.castSucc`.
+
+A version of `Fin.induction` taking `i : Fin (n + 1)` as the first argument.
+-/
+-- FIXME: Performance review
+@[elab_as_elim] def inductionOn (i : Fin (n + 1)) {motive : Fin (n + 1) → Sort _} (zero : motive 0)
+    (succ : ∀ i : Fin n, motive (castSucc i) → motive i.succ) : motive i := induction zero succ i
+
+/-- Define `f : Π i : Fin n.succ, motive i` by separately handling the cases `i = 0` and
+`i = j.succ`, `j : Fin n`. -/
+@[elab_as_elim] def cases {motive : Fin (n + 1) → Sort _}
+    (zero : motive 0) (succ : ∀ i : Fin n, motive i.succ) :
+    ∀ i : Fin (n + 1), motive i := induction zero fun i _ => succ i
+
+@[simp] theorem cases_zero {n} {motive : Fin (n + 1) → Sort _} {zero succ} :
+    @Fin.cases n motive zero succ 0 = zero := rfl
+
+@[simp] theorem cases_succ {n} {motive : Fin (n + 1) → Sort _} {zero succ} (i : Fin n) :
+    @Fin.cases n motive zero succ i.succ = succ i := rfl
+
+@[simp] theorem cases_succ' {n} {motive : Fin (n + 1) → Sort _} {zero succ}
+    {i : Nat} (h : i + 1 < n + 1) :
+    @Fin.cases n motive zero succ ⟨i.succ, h⟩ = succ ⟨i, Nat.lt_of_succ_lt_succ h⟩ := rfl
+
+theorem forall_fin_succ {P : Fin (n + 1) → Prop} : (∀ i, P i) ↔ P 0 ∧ ∀ i : Fin n, P i.succ :=
+  ⟨fun H => ⟨H 0, fun _ => H _⟩, fun ⟨H0, H1⟩ i => Fin.cases H0 H1 i⟩
+
+theorem exists_fin_succ {P : Fin (n + 1) → Prop} : (∃ i, P i) ↔ P 0 ∨ ∃ i : Fin n, P i.succ :=
+  ⟨fun ⟨i, h⟩ => Fin.cases Or.inl (fun i hi => Or.inr ⟨i, hi⟩) i h, fun h =>
+    (h.elim fun h => ⟨0, h⟩) fun ⟨i, hi⟩ => ⟨i.succ, hi⟩⟩
+
+theorem forall_fin_one {p : Fin 1 → Prop} : (∀ i, p i) ↔ p 0 :=
+  ⟨fun h => h _, fun h i => Subsingleton.elim i 0 ▸ h⟩
+
+theorem exists_fin_one {p : Fin 1 → Prop} : (∃ i, p i) ↔ p 0 :=
+  ⟨fun ⟨i, h⟩ => Subsingleton.elim i 0 ▸ h, fun h => ⟨_, h⟩⟩
+
+theorem forall_fin_two {p : Fin 2 → Prop} : (∀ i, p i) ↔ p 0 ∧ p 1 :=
+  forall_fin_succ.trans <| and_congr_right fun _ => forall_fin_one
+
+theorem exists_fin_two {p : Fin 2 → Prop} : (∃ i, p i) ↔ p 0 ∨ p 1 :=
+  exists_fin_succ.trans <| or_congr_right exists_fin_one
+
+theorem fin_two_eq_of_eq_zero_iff : ∀ {a b : Fin 2}, (a = 0 ↔ b = 0) → a = b := by
+  simp only [forall_fin_two]; decide
+
+/--
+Define `motive i` by reverse induction on `i : Fin (n + 1)` via induction on the underlying `Nat`
+value. This function has two arguments: `last` handles the base case on `motive (Fin.last n)`,
+and `cast` defines the inductive step using `motive i.succ`, inducting downwards.
+-/
+@[elab_as_elim] def reverseInduction {motive : Fin (n + 1) → Sort _} (last : motive (Fin.last n))
+    (cast : ∀ i : Fin n, motive i.succ → motive (castSucc i)) (i : Fin (n + 1)) : motive i :=
+  if hi : i = Fin.last n then _root_.cast (congrArg motive hi.symm) last
+  else
+    let j : Fin n := ⟨i, Nat.lt_of_le_of_ne (Nat.le_of_lt_succ i.2) fun h => hi (Fin.ext h)⟩
+    cast _ (reverseInduction last cast j.succ)
+termination_by n + 1 - i
+decreasing_by decreasing_with
+  -- FIXME: we put the proof down here to avoid getting a dummy `have` in the definition
+  try simp only [Nat.succ_sub_succ_eq_sub]
+  exact Nat.add_sub_add_right .. ▸ Nat.sub_lt_sub_left i.2 (Nat.lt_succ_self i)
+
+@[simp] theorem reverseInduction_last {n : Nat} {motive : Fin (n + 1) → Sort _} {zero succ} :
+    (reverseInduction zero succ (Fin.last n) : motive (Fin.last n)) = zero := by
+  rw [reverseInduction]; simp
+
+@[simp] theorem reverseInduction_castSucc {n : Nat} {motive : Fin (n + 1) → Sort _} {zero succ}
+    (i : Fin n) : reverseInduction (motive := motive) zero succ (castSucc i) =
+      succ i (reverseInduction zero succ i.succ) := by
+  rw [reverseInduction, dif_neg (Fin.ne_of_lt (Fin.castSucc_lt_last i))]; rfl
+
+/-- Define `f : Π i : Fin n.succ, motive i` by separately handling the cases `i = Fin.last n` and
+`i = j.castSucc`, `j : Fin n`. -/
+@[elab_as_elim] def lastCases {n : Nat} {motive : Fin (n + 1) → Sort _} (last : motive (Fin.last n))
+    (cast : ∀ i : Fin n, motive (castSucc i)) (i : Fin (n + 1)) : motive i :=
+  reverseInduction last (fun i _ => cast i) i
+
+@[simp] theorem lastCases_last {n : Nat} {motive : Fin (n + 1) → Sort _} {last cast} :
+    (Fin.lastCases last cast (Fin.last n) : motive (Fin.last n)) = last :=
+  reverseInduction_last ..
+
+@[simp] theorem lastCases_castSucc {n : Nat} {motive : Fin (n + 1) → Sort _} {last cast}
+    (i : Fin n) : (Fin.lastCases last cast (Fin.castSucc i) : motive (Fin.castSucc i)) = cast i :=
+  reverseInduction_castSucc ..
+
+/-- Define `f : Π i : Fin (m + n), motive i` by separately handling the cases `i = castAdd n i`,
+`j : Fin m` and `i = natAdd m j`, `j : Fin n`. -/
+@[elab_as_elim] def addCases {m n : Nat} {motive : Fin (m + n) → Sort u}
+    (left : ∀ i, motive (castAdd n i)) (right : ∀ i, motive (natAdd m i))
+    (i : Fin (m + n)) : motive i :=
+  if hi : (i : Nat) < m then (castAdd_castLT n i hi) ▸ (left (castLT i hi))
+  else (natAdd_subNat_cast (Nat.le_of_not_lt hi)) ▸ (right _)
+
+@[simp] theorem addCases_left {m n : Nat} {motive : Fin (m + n) → Sort _} {left right} (i : Fin m) :
+    addCases (motive := motive) left right (Fin.castAdd n i) = left i := by
+  rw [addCases, dif_pos (castAdd_lt _ _)]; rfl
+
+@[simp]
+theorem addCases_right {m n : Nat} {motive : Fin (m + n) → Sort _} {left right} (i : Fin n) :
+    addCases (motive := motive) left right (natAdd m i) = right i := by
+  have : ¬(natAdd m i : Nat) < m := Nat.not_lt.2 (le_coe_natAdd ..)
+  rw [addCases, dif_neg this]; exact eq_of_heq <| (eqRec_heq _ _).trans (by congr 1; simp)
+
+/-! ### add -/
+
+@[simp] theorem ofNat'_add (x : Nat) (lt : 0 < n) (y : Fin n) :
+    Fin.ofNat' x lt + y = Fin.ofNat' (x + y.val) lt := by
+  apply Fin.eq_of_val_eq
+  simp [Fin.ofNat', Fin.add_def]
+
+@[simp] theorem add_ofNat' (x : Fin n) (y : Nat) (lt : 0 < n) :
+    x + Fin.ofNat' y lt = Fin.ofNat' (x.val + y) lt := by
+  apply Fin.eq_of_val_eq
+  simp [Fin.ofNat', Fin.add_def]
+
+/-! ### sub -/
+
+protected theorem coe_sub (a b : Fin n) : ((a - b : Fin n) : Nat) = (a + (n - b)) % n := by
+  cases a; cases b; rfl
+
+@[simp] theorem ofNat'_sub (x : Nat) (lt : 0 < n) (y : Fin n) :
+    Fin.ofNat' x lt - y = Fin.ofNat' (x + (n - y.val)) lt := by
+  apply Fin.eq_of_val_eq
+  simp [Fin.ofNat', Fin.sub_def]
+
+@[simp] theorem sub_ofNat' (x : Fin n) (y : Nat) (lt : 0 < n) :
+    x - Fin.ofNat' y lt = Fin.ofNat' (x.val + (n - y % n)) lt := by
+  apply Fin.eq_of_val_eq
+  simp [Fin.ofNat', Fin.sub_def]
+
+private theorem _root_.Nat.mod_eq_sub_of_lt_two_mul {x n} (h₁ : n ≤ x) (h₂ : x < 2 * n) :
+    x % n = x - n := by
+  rw [Nat.mod_eq, if_pos (by omega), Nat.mod_eq_of_lt (by omega)]
+
+theorem coe_sub_iff_le {a b : Fin n} : (↑(a - b) : Nat) = a - b ↔ b ≤ a := by
+  rw [sub_def, le_def]
+  dsimp only
+  if h : n ≤ a + (n - b) then
+    rw [Nat.mod_eq_sub_of_lt_two_mul h]
+    all_goals omega
+  else
+    rw [Nat.mod_eq_of_lt]
+    all_goals omega
+
+theorem coe_sub_iff_lt {a b : Fin n} : (↑(a - b) : Nat) = n + a - b ↔ a < b := by
+  rw [sub_def, lt_def]
+  dsimp only
+  if h : n ≤ a + (n - b) then
+    rw [Nat.mod_eq_sub_of_lt_two_mul h]
+    all_goals omega
+  else
+    rw [Nat.mod_eq_of_lt]
+    all_goals omega
+
+/-! ### mul -/
+
+theorem val_mul {n : Nat} : ∀ a b : Fin n, (a * b).val = a.val * b.val % n
+  | ⟨_, _⟩, ⟨_, _⟩ => rfl
+
+theorem coe_mul {n : Nat} : ∀ a b : Fin n, ((a * b : Fin n) : Nat) = a * b % n
+  | ⟨_, _⟩, ⟨_, _⟩ => rfl
+
+protected theorem mul_one (k : Fin (n + 1)) : k * 1 = k := by
+  match n with
+  | 0 => exact Subsingleton.elim (α := Fin 1) ..
+  | n+1 => simp [ext_iff, mul_def, Nat.mod_eq_of_lt (is_lt k)]
+
+protected theorem mul_comm (a b : Fin n) : a * b = b * a :=
+  ext <| by rw [mul_def, mul_def, Nat.mul_comm]
+
+protected theorem mul_assoc (a b c : Fin n) : a * b * c = a * (b * c) := by
+  apply eq_of_val_eq
+  simp only [val_mul]
+  rw [← Nat.mod_eq_of_lt a.isLt, ← Nat.mod_eq_of_lt b.isLt, ← Nat.mod_eq_of_lt c.isLt]
+  simp only [← Nat.mul_mod, Nat.mul_assoc]
+
+protected theorem one_mul (k : Fin (n + 1)) : (1 : Fin (n + 1)) * k = k := by
+  rw [Fin.mul_comm, Fin.mul_one]
+
+protected theorem mul_zero (k : Fin (n + 1)) : k * 0 = 0 := by simp [ext_iff, mul_def]
+
+protected theorem zero_mul (k : Fin (n + 1)) : (0 : Fin (n + 1)) * k = 0 := by
+  simp [ext_iff, mul_def]
+
+end Fin
+
+namespace USize
+
+@[simp] theorem lt_def {a b : USize} : a < b ↔ a.toNat < b.toNat := .rfl
+
+@[simp] theorem le_def {a b : USize} : a ≤ b ↔ a.toNat ≤ b.toNat := .rfl
+
+@[simp] theorem zero_toNat : (0 : USize).toNat = 0 := Nat.zero_mod _
+
+@[simp] theorem mod_toNat (a b : USize) : (a % b).toNat = a.toNat % b.toNat :=
+  Fin.mod_val ..
+
+@[simp] theorem div_toNat (a b : USize) : (a / b).toNat = a.toNat / b.toNat :=
+  Fin.div_val ..
+
+@[simp] theorem modn_toNat (a : USize) (b : Nat) : (a.modn b).toNat = a.toNat % b :=
+  Fin.modn_val ..
+
+theorem mod_lt (a b : USize) (h : 0 < b) : a % b < b := USize.modn_lt _ (by simp at h; exact h)
+
+theorem toNat.inj : ∀ {a b : USize}, a.toNat = b.toNat → a = b
+  | ⟨_, _⟩, ⟨_, _⟩, rfl => rfl
+
+end USize

src/Init/Data/FloatArray/Basic.lean

@@ -58,9 +58,13 @@ def get? (ds : FloatArray) (i : Nat) : Option Float :=
 instance : GetElem FloatArray Nat Float fun xs i => i < xs.size where
   getElem xs i h := xs.get ⟨i, h⟩
 
+instance : LawfulGetElem FloatArray Nat Float fun xs i => i < xs.size where
+
 instance : GetElem FloatArray USize Float fun xs i => i.val < xs.size where
   getElem xs i h := xs.uget i h
 
+instance : LawfulGetElem FloatArray USize Float fun xs i => i.val < xs.size where
+
 @[extern "lean_float_array_uset"]
 def uset : (a : FloatArray) → (i : USize) → Float → i.toNat < a.size → FloatArray
   | ⟨ds⟩, i, v, h => ⟨ds.uset i v h⟩

src/Init/Data/Int.lean

@@ -5,3 +5,10 @@ Authors: Leonardo de Moura
 -/
 prelude
 import Init.Data.Int.Basic
+import Init.Data.Int.Bitwise
+import Init.Data.Int.DivMod
+import Init.Data.Int.DivModLemmas
+import Init.Data.Int.Gcd
+import Init.Data.Int.Lemmas
+import Init.Data.Int.Order
+import Init.Data.Int.Pow

src/Init/Data/Int/Basic.lean

@@ -6,7 +6,7 @@ Authors: Jeremy Avigad, Leonardo de Moura
 The integers, with addition, multiplication, and subtraction.
 -/
 prelude
-import Init.Coe
+import Init.Data.Cast
 import Init.Data.Nat.Div
 import Init.Data.List.Basic
 set_option linter.missingDocs true -- keep it documented
@@ -47,14 +47,35 @@ inductive Int : Type where
 attribute [extern "lean_nat_to_int"] Int.ofNat
 attribute [extern "lean_int_neg_succ_of_nat"] Int.negSucc
 
-instance : Coe Nat Int := ⟨Int.ofNat⟩
+instance : NatCast Int where natCast n := Int.ofNat n
 
 instance instOfNat : OfNat Int n where
   ofNat := Int.ofNat n
 
 namespace Int
+
+/--
+`-[n+1]` is suggestive notation for `negSucc n`, which is the second constructor of
+`Int` for making strictly negative numbers by mapping `n : Nat` to `-(n + 1)`.
+-/
+scoped notation "-[" n "+1]" => negSucc n
+
 instance : Inhabited Int := ⟨ofNat 0⟩
 
+@[simp] theorem default_eq_zero : default = (0 : Int) := rfl
+
+protected theorem zero_ne_one : (0 : Int) ≠ 1 := nofun
+
+/-! ## Coercions -/
+
+@[simp] theorem ofNat_eq_coe : Int.ofNat n = Nat.cast n := rfl
+
+@[simp] theorem ofNat_zero : ((0 : Nat) : Int) = 0 := rfl
+
+@[simp] theorem ofNat_one  : ((1 : Nat) : Int) = 1 := rfl
+
+theorem ofNat_two : ((2 : Nat) : Int) = 2 := rfl
+
 /-- Negation of a natural number. -/
 def negOfNat : Nat → Int
   | 0      => 0
@@ -79,7 +100,7 @@ protected def neg (n : @& Int) : Int :=
   ```
 -/
 @[default_instance mid]
-instance : Neg Int where
+instance instNegInt : Neg Int where
   neg := Int.neg
 
 /-- Subtraction of two natural numbers. -/
@@ -100,10 +121,10 @@ set_option bootstrap.genMatcherCode false in
 @[extern "lean_int_add"]
 protected def add (m n : @& Int) : Int :=
   match m, n with
-  | ofNat m,   ofNat n   => ofNat (m + n)
-  | ofNat m,   negSucc n => subNatNat m (succ n)
-  | negSucc m, ofNat n   => subNatNat n (succ m)
-  | negSucc m, negSucc n => negSucc (succ (m + n))
+  | ofNat m, ofNat n => ofNat (m + n)
+  | ofNat m, -[n +1] => subNatNat m (succ n)
+  | -[m +1], ofNat n => subNatNat n (succ m)
+  | -[m +1], -[n +1] => negSucc (succ (m + n))
 
 instance : Add Int where
   add := Int.add
@@ -121,10 +142,10 @@ set_option bootstrap.genMatcherCode false in
 @[extern "lean_int_mul"]
 protected def mul (m n : @& Int) : Int :=
   match m, n with
-  | ofNat m,   ofNat n   => ofNat (m * n)
-  | ofNat m,   negSucc n => negOfNat (m * succ n)
-  | negSucc m, ofNat n   => negOfNat (succ m * n)
-  | negSucc m, negSucc n => ofNat (succ m * succ n)
+  | ofNat m, ofNat n => ofNat (m * n)
+  | ofNat m, -[n +1] => negOfNat (m * succ n)
+  | -[m +1], ofNat n => negOfNat (succ m * n)
+  | -[m +1], -[n +1] => ofNat (succ m * succ n)
 
 instance : Mul Int where
   mul := Int.mul
@@ -139,8 +160,7 @@ instance : Mul Int where
 
   Implemented by efficient native code. -/
 @[extern "lean_int_sub"]
-protected def sub (m n : @& Int) : Int :=
-  m + (- n)
+protected def sub (m n : @& Int) : Int := m + (- n)
 
 instance : Sub Int where
   sub := Int.sub
@@ -153,13 +173,13 @@ inductive NonNeg : Int → Prop where
 /-- Definition of `a ≤ b`, encoded as `b - a ≥ 0`. -/
 protected def le (a b : Int) : Prop := NonNeg (b - a)
 
-instance : LE Int where
+instance instLEInt : LE Int where
   le := Int.le
 
 /-- Definition of `a < b`, encoded as `a + 1 ≤ b`. -/
 protected def lt (a b : Int) : Prop := (a + 1) ≤ b
 
-instance : LT Int where
+instance instLTInt : LT Int where
   lt := Int.lt
 
 set_option bootstrap.genMatcherCode false in
@@ -178,11 +198,11 @@ protected def decEq (a b : @& Int) : Decidable (a = b) :=
   | ofNat a, ofNat b => match decEq a b with
     | isTrue h  => isTrue  <| h ▸ rfl
     | isFalse h => isFalse <| fun h' => Int.noConfusion h' (fun h' => absurd h' h)
-  | negSucc a, negSucc b => match decEq a b with
+  | ofNat _, -[_ +1] => isFalse <| fun h => Int.noConfusion h
+  | -[_ +1], ofNat _ => isFalse <| fun h => Int.noConfusion h
+  | -[a +1], -[b +1] => match decEq a b with
     | isTrue h  => isTrue  <| h ▸ rfl
     | isFalse h => isFalse <| fun h' => Int.noConfusion h' (fun h' => absurd h' h)
-  | ofNat _, negSucc _ => isFalse <| fun h => Int.noConfusion h
-  | negSucc _, ofNat _ => isFalse <| fun h => Int.noConfusion h
 
 instance : DecidableEq Int := Int.decEq
 
@@ -199,8 +219,8 @@ set_option bootstrap.genMatcherCode false in
 @[extern "lean_int_dec_nonneg"]
 private def decNonneg (m : @& Int) : Decidable (NonNeg m) :=
   match m with
-  | ofNat m   => isTrue <| NonNeg.mk m
-  | negSucc _ => isFalse <| fun h => nomatch h
+  | ofNat m => isTrue <| NonNeg.mk m
+  | -[_ +1] => isFalse <| fun h => nomatch h
 
 /-- Decides whether `a ≤ b`.
 
@@ -241,85 +261,21 @@ set_option bootstrap.genMatcherCode false in
 @[extern "lean_nat_abs"]
 def natAbs (m : @& Int) : Nat :=
   match m with
-  | ofNat m   => m
-  | negSucc m => m.succ
+  | ofNat m => m
+  | -[m +1] => m.succ
 
-/-- Integer division. This function uses the
-  [*"T-rounding"*][t-rounding] (**T**runcation-rounding) convention,
-  meaning that it rounds toward zero. Also note that division by zero
-  is defined to equal zero.
+/-! ## sign -/
 
-  The relation between integer division and modulo is found in [the
-  `Int.mod_add_div` theorem in std][theo mod_add_div] which states
-  that `a % b + b * (a / b) = a`, unconditionally.
+/--
+Returns the "sign" of the integer as another integer: `1` for positive numbers,
+`-1` for negative numbers, and `0` for `0`.
+-/
+def sign : Int → Int
+  | Int.ofNat (succ _) => 1
+  | Int.ofNat 0 => 0
+  | -[_+1]      => -1
 
-  [t-rounding]: https://dl.acm.org/doi/pdf/10.1145/128861.128862
-  [theo mod_add_div]: https://leanprover-community.github.io/mathlib4_docs/find/?pattern=Int.mod_add_div#doc
-
-  Examples:
-
-  ```
-  #eval (7 : Int) / (0 : Int) -- 0
-  #eval (0 : Int) / (7 : Int) -- 0
-
-  #eval (12 : Int) / (6 : Int) -- 2
-  #eval (12 : Int) / (-6 : Int) -- -2
-  #eval (-12 : Int) / (6 : Int) -- -2
-  #eval (-12 : Int) / (-6 : Int) -- 2
-
-  #eval (12 : Int) / (7 : Int) -- 1
-  #eval (12 : Int) / (-7 : Int) -- -1
-  #eval (-12 : Int) / (7 : Int) -- -1
-  #eval (-12 : Int) / (-7 : Int) -- 1
-  ```
-
-  Implemented by efficient native code. -/
-@[extern "lean_int_div"]
-def div : (@& Int) → (@& Int) → Int
-  | ofNat m,   ofNat n   => ofNat (m / n)
-  | ofNat m,   negSucc n => -ofNat (m / succ n)
-  | negSucc m, ofNat n   => -ofNat (succ m / n)
-  | negSucc m, negSucc n => ofNat (succ m / succ n)
-
-instance : Div Int where
-  div := Int.div
-
-/-- Integer modulo. This function uses the
-  [*"T-rounding"*][t-rounding] (**T**runcation-rounding) convention
-  to pair with `Int.div`, meaning that `a % b + b * (a / b) = a`
-  unconditionally (see [`Int.mod_add_div`][theo mod_add_div]). In
-  particular, `a % 0 = a`.
-
-  [t-rounding]: https://dl.acm.org/doi/pdf/10.1145/128861.128862
-  [theo mod_add_div]: https://leanprover-community.github.io/mathlib4_docs/find/?pattern=Int.mod_add_div#doc
-
-  Examples:
-
-  ```
-  #eval (7 : Int) % (0 : Int) -- 7
-  #eval (0 : Int) % (7 : Int) -- 0
-
-  #eval (12 : Int) % (6 : Int) -- 0
-  #eval (12 : Int) % (-6 : Int) -- 0
-  #eval (-12 : Int) % (6 : Int) -- 0
-  #eval (-12 : Int) % (-6 : Int) -- 0
-
-  #eval (12 : Int) % (7 : Int) -- 5
-  #eval (12 : Int) % (-7 : Int) -- 5
-  #eval (-12 : Int) % (7 : Int) -- 2
-  #eval (-12 : Int) % (-7 : Int) -- 2
-  ```
-
-  Implemented by efficient native code. -/
-@[extern "lean_int_mod"]
-def mod : (@& Int) → (@& Int) → Int
-  | ofNat m,   ofNat n   => ofNat (m % n)
-  | ofNat m,   negSucc n => ofNat (m % succ n)
-  | negSucc m, ofNat n   => -ofNat (succ m % n)
-  | negSucc m, negSucc n => -ofNat (succ m % succ n)
-
-instance : Mod Int where
-  mod := Int.mod
+/-! ## Conversion -/
 
 /-- Turns an integer into a natural number, negative numbers become
   `0`.
@@ -334,6 +290,25 @@ def toNat : Int → Nat
   | ofNat n   => n
   | negSucc _ => 0
 
+/--
+* If `n : Nat`, then `int.toNat' n = some n`
+* If `n : Int` is negative, then `int.toNat' n = none`.
+-/
+def toNat' : Int → Option Nat
+  | (n : Nat) => some n
+  | -[_+1] => none
+
+/-! ## divisibility -/
+
+/--
+Divisibility of integers. `a ∣ b` (typed as `\|`) says that
+there is some `c` such that `b = a * c`.
+-/
+instance : Dvd Int where
+  dvd a b := Exists (fun c => b = a * c)
+
+/-! ## Powers -/
+
 /-- Power of an integer to some natural number.
 
   ```
@@ -359,3 +334,27 @@ instance : Min Int := minOfLe
 instance : Max Int := maxOfLe
 
 end Int
+
+/--
+The canonical homomorphism `Int → R`.
+In most use cases `R` will have a ring structure and this will be a ring homomorphism.
+-/
+class IntCast (R : Type u) where
+  /-- The canonical map `Int → R`. -/
+  protected intCast : Int → R
+
+instance : IntCast Int where intCast n := n
+
+/--
+Apply the canonical homomorphism from `Int` to a type `R` from an `IntCast R` instance.
+
+In Mathlib there will be such a homomorphism whenever `R` is an additive group with a `1`.
+-/
+@[coe, reducible, match_pattern] protected def Int.cast {R : Type u} [IntCast R] : Int → R :=
+  IntCast.intCast
+
+-- see the notes about coercions into arbitrary types in the module doc-string
+instance [IntCast R] : CoeTail Int R where coe := Int.cast
+
+-- see the notes about coercions into arbitrary types in the module doc-string
+instance [IntCast R] : CoeHTCT Int R where coe := Int.cast

src/Init/Data/Int/Bitwise.lean

@@ -0,0 +1,50 @@
+/-
+Copyright (c) 2022 Mario Carneiro. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Mario Carneiro
+-/
+prelude
+import Init.Data.Int.Basic
+import Init.Data.Nat.Bitwise.Basic
+
+namespace Int
+
+/-! ## bit operations -/
+
+/--
+Bitwise not
+
+Interprets the integer as an infinite sequence of bits in two's complement
+and complements each bit.
+```
+~~~(0:Int) = -1
+~~~(1:Int) = -2
+~~~(-1:Int) = 0
+```
+-/
+protected def not : Int -> Int
+  | Int.ofNat n => Int.negSucc n
+  | Int.negSucc n => Int.ofNat n
+
+instance : Complement Int := ⟨.not⟩
+
+/--
+Bitwise shift right.
+
+Conceptually, this treats the integer as an infinite sequence of bits in two's
+complement and shifts the value to the right.
+
+```lean
+( 0b0111:Int) >>> 1 =  0b0011
+( 0b1000:Int) >>> 1 =  0b0100
+(-0b1000:Int) >>> 1 = -0b0100
+(-0b0111:Int) >>> 1 = -0b0100
+```
+-/
+protected def shiftRight : Int → Nat → Int
+  | Int.ofNat n, s => Int.ofNat (n >>> s)
+  | Int.negSucc n, s => Int.negSucc (n >>> s)
+
+instance : HShiftRight Int Nat Int := ⟨.shiftRight⟩
+
+end Int

src/Init/Data/Int/DivMod.lean

@@ -0,0 +1,209 @@
+/-
+Copyright (c) 2016 Jeremy Avigad. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Jeremy Avigad, Mario Carneiro
+-/
+prelude
+import Init.Data.Int.Basic
+
+open Nat
+
+namespace Int
+
+/-! ## Quotient and remainder
+
+There are three main conventions for integer division,
+referred here as the E, F, T rounding conventions.
+All three pairs satisfy the identity `x % y + (x / y) * y = x` unconditionally,
+and satisfy `x / 0 = 0` and `x % 0 = x`.
+-/
+
+/-! ### T-rounding division -/
+
+/--
+`div` uses the [*"T-rounding"*][t-rounding]
+(**T**runcation-rounding) convention, meaning that it rounds toward
+zero. Also note that division by zero is defined to equal zero.
+
+  The relation between integer division and modulo is found in
+  `Int.mod_add_div` which states that
+  `a % b + b * (a / b) = a`, unconditionally.
+
+  [t-rounding]: https://dl.acm.org/doi/pdf/10.1145/128861.128862 [theo
+  mod_add_div]:
+  https://leanprover-community.github.io/mathlib4_docs/find/?pattern=Int.mod_add_div#doc
+
+  Examples:
+
+  ```
+  #eval (7 : Int) / (0 : Int) -- 0
+  #eval (0 : Int) / (7 : Int) -- 0
+
+  #eval (12 : Int) / (6 : Int) -- 2
+  #eval (12 : Int) / (-6 : Int) -- -2
+  #eval (-12 : Int) / (6 : Int) -- -2
+  #eval (-12 : Int) / (-6 : Int) -- 2
+
+  #eval (12 : Int) / (7 : Int) -- 1
+  #eval (12 : Int) / (-7 : Int) -- -1
+  #eval (-12 : Int) / (7 : Int) -- -1
+  #eval (-12 : Int) / (-7 : Int) -- 1
+  ```
+
+  Implemented by efficient native code.
+-/
+@[extern "lean_int_div"]
+def div : (@& Int) → (@& Int) → Int
+  | ofNat m, ofNat n =>  ofNat (m / n)
+  | ofNat m, -[n +1] => -ofNat (m / succ n)
+  | -[m +1], ofNat n => -ofNat (succ m / n)
+  | -[m +1], -[n +1] =>  ofNat (succ m / succ n)
+
+/-- Integer modulo. This function uses the
+  [*"T-rounding"*][t-rounding] (**T**runcation-rounding) convention
+  to pair with `Int.div`, meaning that `a % b + b * (a / b) = a`
+  unconditionally (see [`Int.mod_add_div`][theo mod_add_div]). In
+  particular, `a % 0 = a`.
+
+  [t-rounding]: https://dl.acm.org/doi/pdf/10.1145/128861.128862
+  [theo mod_add_div]: https://leanprover-community.github.io/mathlib4_docs/find/?pattern=Int.mod_add_div#doc
+
+  Examples:
+
+  ```
+  #eval (7 : Int) % (0 : Int) -- 7
+  #eval (0 : Int) % (7 : Int) -- 0
+
+  #eval (12 : Int) % (6 : Int) -- 0
+  #eval (12 : Int) % (-6 : Int) -- 0
+  #eval (-12 : Int) % (6 : Int) -- 0
+  #eval (-12 : Int) % (-6 : Int) -- 0
+
+  #eval (12 : Int) % (7 : Int) -- 5
+  #eval (12 : Int) % (-7 : Int) -- 5
+  #eval (-12 : Int) % (7 : Int) -- 2
+  #eval (-12 : Int) % (-7 : Int) -- 2
+  ```
+
+  Implemented by efficient native code. -/
+@[extern "lean_int_mod"]
+def mod : (@& Int) → (@& Int) → Int
+  | ofNat m, ofNat n =>  ofNat (m % n)
+  | ofNat m, -[n +1] =>  ofNat (m % succ n)
+  | -[m +1], ofNat n => -ofNat (succ m % n)
+  | -[m +1], -[n +1] => -ofNat (succ m % succ n)
+
+/-! ### F-rounding division
+This pair satisfies `fdiv x y = floor (x / y)`.
+-/
+
+/--
+Integer division. This version of division uses the F-rounding convention
+(flooring division), in which `Int.fdiv x y` satisfies `fdiv x y = floor (x / y)`
+and `Int.fmod` is the unique function satisfying `fmod x y + (fdiv x y) * y = x`.
+-/
+def fdiv : Int → Int → Int
+  | 0,       _       => 0
+  | ofNat m, ofNat n => ofNat (m / n)
+  | ofNat (succ m), -[n+1] => -[m / succ n +1]
+  | -[_+1],  0       => 0
+  | -[m+1],  ofNat (succ n) => -[m / succ n +1]
+  | -[m+1],  -[n+1]  => ofNat (succ m / succ n)
+
+/--
+Integer modulus. This version of `Int.mod` uses the F-rounding convention
+(flooring division), in which `Int.fdiv x y` satisfies `fdiv x y = floor (x / y)`
+and `Int.fmod` is the unique function satisfying `fmod x y + (fdiv x y) * y = x`.
+-/
+def fmod : Int → Int → Int
+  | 0,       _       => 0
+  | ofNat m, ofNat n => ofNat (m % n)
+  | ofNat (succ m),  -[n+1]  => subNatNat (m % succ n) n
+  | -[m+1],  ofNat n => subNatNat n (succ (m % n))
+  | -[m+1],  -[n+1]  => -ofNat (succ m % succ n)
+
+/-! ### E-rounding division
+This pair satisfies `0 ≤ mod x y < natAbs y` for `y ≠ 0`.
+-/
+
+/--
+Integer division. This version of `Int.div` uses the E-rounding convention
+(euclidean division), in which `Int.emod x y` satisfies `0 ≤ mod x y < natAbs y` for `y ≠ 0`
+and `Int.ediv` is the unique function satisfying `emod x y + (ediv x y) * y = x`.
+-/
+@[extern "lean_int_ediv"]
+def ediv : (@& Int) → (@& Int) → Int
+  | ofNat m, ofNat n => ofNat (m / n)
+  | ofNat m, -[n+1]  => -ofNat (m / succ n)
+  | -[_+1],  0       => 0
+  | -[m+1],  ofNat (succ n) => -[m / succ n +1]
+  | -[m+1],  -[n+1]  => ofNat (succ (m / succ n))
+
+/--
+Integer modulus. This version of `Int.mod` uses the E-rounding convention
+(euclidean division), in which `Int.emod x y` satisfies `0 ≤ emod x y < natAbs y` for `y ≠ 0`
+and `Int.ediv` is the unique function satisfying `emod x y + (ediv x y) * y = x`.
+-/
+@[extern "lean_int_emod"]
+def emod : (@& Int) → (@& Int) → Int
+  | ofNat m, n => ofNat (m % natAbs n)
+  | -[m+1],  n => subNatNat (natAbs n) (succ (m % natAbs n))
+
+/--
+The Div and Mod syntax uses ediv and emod for compatibility with SMTLIb and mathematical
+reasoning tends to be easier.
+-/
+instance : Div Int where
+  div := Int.ediv
+instance : Mod Int where
+  mod := Int.emod
+
+@[simp, norm_cast] theorem ofNat_ediv (m n : Nat) : (↑(m / n) : Int) = ↑m / ↑n := rfl
+
+theorem ofNat_div (m n : Nat) : ↑(m / n) = div ↑m ↑n := rfl
+
+theorem ofNat_fdiv : ∀ m n : Nat, ↑(m / n) = fdiv ↑m ↑n
+  | 0, _ => by simp [fdiv]
+  | succ _, _ => rfl
+
+/-!
+# `bmod` ("balanced" mod)
+
+Balanced mod (and balanced div) are a division and modulus pair such
+that `b * (Int.bdiv a b) + Int.bmod a b = a` and `b/2 ≤ Int.bmod a b <
+b/2` for all `a : Int` and `b > 0`.
+
+This is used in Omega as well as signed bitvectors.
+-/
+
+/--
+Balanced modulus.  This version of Integer modulus uses the
+balanced rounding convention, which guarantees that
+`m/2 ≤ bmod x m < m/2` for `m ≠ 0` and `bmod x m` is congruent
+to `x` modulo `m`.
+
+If `m = 0`, then `bmod x m = x`.
+-/
+def bmod (x : Int) (m : Nat) : Int :=
+  let r := x % m
+  if r < (m + 1) / 2 then
+    r
+  else
+    r - m
+
+/--
+Balanced division.  This returns the unique integer so that
+`b * (Int.bdiv a b) + Int.bmod a b = a`.
+-/
+def bdiv (x : Int) (m : Nat) : Int :=
+  if m = 0 then
+    0
+  else
+    let q := x / m
+    let r := x % m
+    if r < (m + 1) / 2 then
+      q
+    else
+      q + 1
+
+end Int

src/Init/Data/Int/Gcd.lean

@@ -0,0 +1,55 @@
+/-
+Copyright (c) 2022 Mario Carneiro. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Mario Carneiro
+-/
+prelude
+import Init.Data.Int.Basic
+import Init.Data.Nat.Gcd
+import Init.Data.Nat.Lcm
+import Init.Data.Int.DivModLemmas
+
+/-!
+Definition and lemmas for gcd and lcm over Int
+-/
+namespace Int
+
+/-! ## gcd -/
+
+/-- Computes the greatest common divisor of two integers, as a `Nat`. -/
+def gcd (m n : Int) : Nat := m.natAbs.gcd n.natAbs
+
+theorem gcd_dvd_left {a b : Int} : (gcd a b : Int) ∣ a := by
+  have := Nat.gcd_dvd_left a.natAbs b.natAbs
+  rw [← Int.ofNat_dvd] at this
+  exact Int.dvd_trans this natAbs_dvd_self
+
+theorem gcd_dvd_right {a b : Int} : (gcd a b : Int) ∣ b := by
+  have := Nat.gcd_dvd_right a.natAbs b.natAbs
+  rw [← Int.ofNat_dvd] at this
+  exact Int.dvd_trans this natAbs_dvd_self
+
+@[simp] theorem one_gcd {a : Int} : gcd 1 a = 1 := by simp [gcd]
+@[simp] theorem gcd_one {a : Int} : gcd a 1 = 1 := by simp [gcd]
+
+@[simp] theorem neg_gcd {a b : Int} : gcd (-a) b = gcd a b := by simp [gcd]
+@[simp] theorem gcd_neg {a b : Int} : gcd a (-b) = gcd a b := by simp [gcd]
+
+/-! ## lcm -/
+
+/-- Computes the least common multiple of two integers, as a `Nat`. -/
+def lcm (m n : Int) : Nat := m.natAbs.lcm n.natAbs
+
+theorem lcm_ne_zero (hm : m ≠ 0) (hn : n ≠ 0) : lcm m n ≠ 0 := by
+  simp only [lcm]
+  apply Nat.lcm_ne_zero <;> simpa
+
+theorem dvd_lcm_left {a b : Int} : a ∣ lcm a b :=
+  Int.dvd_trans dvd_natAbs_self (Int.ofNat_dvd.mpr (Nat.dvd_lcm_left a.natAbs b.natAbs))
+
+theorem dvd_lcm_right {a b : Int} : b ∣ lcm a b :=
+  Int.dvd_trans dvd_natAbs_self (Int.ofNat_dvd.mpr (Nat.dvd_lcm_right a.natAbs b.natAbs))
+
+@[simp] theorem lcm_self {a : Int} : lcm a a = a.natAbs := Nat.lcm_self _
+
+end Int

src/Init/Data/Int/Lemmas.lean

@@ -0,0 +1,520 @@
+/-
+Copyright (c) 2016 Jeremy Avigad. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Jeremy Avigad, Deniz Aydin, Floris van Doorn, Mario Carneiro
+-/
+prelude
+import Init.Data.Int.Basic
+import Init.Conv
+import Init.NotationExtra
+
+namespace Int
+
+open Nat
+
+/-! ## Definitions of basic functions -/
+
+theorem subNatNat_of_sub_eq_zero {m n : Nat} (h : n - m = 0) : subNatNat m n = ↑(m - n) := by
+  rw [subNatNat, h, ofNat_eq_coe]
+
+theorem subNatNat_of_sub_eq_succ {m n k : Nat} (h : n - m = succ k) : subNatNat m n = -[k+1] := by
+  rw [subNatNat, h]
+
+@[simp] protected theorem neg_zero : -(0:Int) = 0 := rfl
+
+@[norm_cast] theorem ofNat_add (n m : Nat) : (↑(n + m) : Int) = n + m := rfl
+@[norm_cast] theorem ofNat_mul (n m : Nat) : (↑(n * m) : Int) = n * m := rfl
+theorem ofNat_succ (n : Nat) : (succ n : Int) = n + 1 := rfl
+
+@[local simp] theorem neg_ofNat_zero : -((0 : Nat) : Int) = 0 := rfl
+@[local simp] theorem neg_ofNat_succ (n : Nat) : -(succ n : Int) = -[n+1] := rfl
+@[local simp] theorem neg_negSucc (n : Nat) : -(-[n+1]) = succ n := rfl
+
+theorem negSucc_coe (n : Nat) : -[n+1] = -↑(n + 1) := rfl
+
+theorem negOfNat_eq : negOfNat n = -ofNat n := rfl
+
+/-! ## These are only for internal use -/
+
+@[simp] theorem add_def {a b : Int} : Int.add a b = a + b := rfl
+
+@[local simp] theorem ofNat_add_ofNat (m n : Nat) : (↑m + ↑n : Int) = ↑(m + n) := rfl
+@[local simp] theorem ofNat_add_negSucc (m n : Nat) : ↑m + -[n+1] = subNatNat m (succ n) := rfl
+@[local simp] theorem negSucc_add_ofNat (m n : Nat) : -[m+1] + ↑n = subNatNat n (succ m) := rfl
+@[local simp] theorem negSucc_add_negSucc (m n : Nat) : -[m+1] + -[n+1] = -[succ (m + n) +1] := rfl
+
+@[simp] theorem mul_def {a b : Int} : Int.mul a b = a * b := rfl
+
+@[local simp] theorem ofNat_mul_ofNat (m n : Nat) : (↑m * ↑n : Int) = ↑(m * n) := rfl
+@[local simp] theorem ofNat_mul_negSucc' (m n : Nat) : ↑m * -[n+1] = negOfNat (m * succ n) := rfl
+@[local simp] theorem negSucc_mul_ofNat' (m n : Nat) : -[m+1] * ↑n = negOfNat (succ m * n) := rfl
+@[local simp] theorem negSucc_mul_negSucc' (m n : Nat) :
+    -[m+1] * -[n+1] = ofNat (succ m * succ n) := rfl
+
+/- ## some basic functions and properties -/
+
+@[norm_cast] theorem ofNat_inj : ((m : Nat) : Int) = (n : Nat) ↔ m = n := ⟨ofNat.inj, congrArg _⟩
+
+theorem ofNat_eq_zero : ((n : Nat) : Int) = 0 ↔ n = 0 := ofNat_inj
+
+theorem ofNat_ne_zero : ((n : Nat) : Int) ≠ 0 ↔ n ≠ 0 := not_congr ofNat_eq_zero
+
+theorem negSucc_inj : negSucc m = negSucc n ↔ m = n := ⟨negSucc.inj, fun H => by simp [H]⟩
+
+theorem negSucc_eq (n : Nat) : -[n+1] = -((n : Int) + 1) := rfl
+
+@[simp] theorem negSucc_ne_zero (n : Nat) : -[n+1] ≠ 0 := nofun
+
+@[simp] theorem zero_ne_negSucc (n : Nat) : 0 ≠ -[n+1] := nofun
+
+@[simp, norm_cast] theorem Nat.cast_ofNat_Int :
+  (Nat.cast (no_index (OfNat.ofNat n)) : Int) = OfNat.ofNat n := rfl
+
+/- ## neg -/
+
+@[simp] protected theorem neg_neg : ∀ a : Int, -(-a) = a
+  | 0      => rfl
+  | succ _ => rfl
+  | -[_+1] => rfl
+
+protected theorem neg_inj {a b : Int} : -a = -b ↔ a = b :=
+  ⟨fun h => by rw [← Int.neg_neg a, ← Int.neg_neg b, h], congrArg _⟩
+
+@[simp] protected theorem neg_eq_zero : -a = 0 ↔ a = 0 := Int.neg_inj (b := 0)
+
+protected theorem neg_ne_zero : -a ≠ 0 ↔ a ≠ 0 := not_congr Int.neg_eq_zero
+
+protected theorem sub_eq_add_neg {a b : Int} : a - b = a + -b := rfl
+
+theorem add_neg_one (i : Int) : i + -1 = i - 1 := rfl
+
+/- ## basic properties of subNatNat -/
+
+-- @[elabAsElim] -- TODO(Mario): unexpected eliminator resulting type
+theorem subNatNat_elim (m n : Nat) (motive : Nat → Nat → Int → Prop)
+    (hp : ∀ i n, motive (n + i) n i)
+    (hn : ∀ i m, motive m (m + i + 1) -[i+1]) :
+    motive m n (subNatNat m n) := by
+  unfold subNatNat
+  match h : n - m with
+  | 0 =>
+    have ⟨k, h⟩ := Nat.le.dest (Nat.le_of_sub_eq_zero h)
+    rw [h.symm, Nat.add_sub_cancel_left]; apply hp
+  | succ k =>
+    rw [Nat.sub_eq_iff_eq_add (Nat.le_of_lt (Nat.lt_of_sub_eq_succ h))] at h
+    rw [h, Nat.add_comm]; apply hn
+
+theorem subNatNat_add_left : subNatNat (m + n) m = n := by
+  unfold subNatNat
+  rw [Nat.sub_eq_zero_of_le (Nat.le_add_right ..), Nat.add_sub_cancel_left, ofNat_eq_coe]
+
+theorem subNatNat_add_right : subNatNat m (m + n + 1) = negSucc n := by
+  simp [subNatNat, Nat.add_assoc, Nat.add_sub_cancel_left]
+
+theorem subNatNat_add_add (m n k : Nat) : subNatNat (m + k) (n + k) = subNatNat m n := by
+  apply subNatNat_elim m n (fun m n i => subNatNat (m + k) (n + k) = i)
+  focus
+    intro i j
+    rw [Nat.add_assoc, Nat.add_comm i k, ← Nat.add_assoc]
+    exact subNatNat_add_left
+  focus
+    intro i j
+    rw [Nat.add_assoc j i 1, Nat.add_comm j (i+1), Nat.add_assoc, Nat.add_comm (i+1) (j+k)]
+    exact subNatNat_add_right
+
+theorem subNatNat_of_le {m n : Nat} (h : n ≤ m) : subNatNat m n = ↑(m - n) :=
+  subNatNat_of_sub_eq_zero (Nat.sub_eq_zero_of_le h)
+
+theorem subNatNat_of_lt {m n : Nat} (h : m < n) : subNatNat m n = -[pred (n - m) +1] :=
+  subNatNat_of_sub_eq_succ <| (Nat.succ_pred_eq_of_pos (Nat.sub_pos_of_lt h)).symm
+
+/- # Additive group properties -/
+
+/- addition -/
+
+protected theorem add_comm : ∀ a b : Int, a + b = b + a
+  | ofNat n, ofNat m => by simp [Nat.add_comm]
+  | ofNat _, -[_+1]  => rfl
+  | -[_+1],  ofNat _ => rfl
+  | -[_+1],  -[_+1]  => by simp [Nat.add_comm]
+
+@[simp] protected theorem add_zero : ∀ a : Int, a + 0 = a
+  | ofNat _ => rfl
+  | -[_+1]  => rfl
+
+@[simp] protected theorem zero_add (a : Int) : 0 + a = a := Int.add_comm .. ▸ a.add_zero
+
+theorem ofNat_add_negSucc_of_lt (h : m < n.succ) : ofNat m + -[n+1] = -[n - m+1] :=
+  show subNatNat .. = _ by simp [succ_sub (le_of_lt_succ h), subNatNat]
+
+theorem subNatNat_sub (h : n ≤ m) (k : Nat) : subNatNat (m - n) k = subNatNat m (k + n) := by
+  rwa [← subNatNat_add_add _ _ n, Nat.sub_add_cancel]
+
+theorem subNatNat_add (m n k : Nat) : subNatNat (m + n) k = m + subNatNat n k := by
+  cases n.lt_or_ge k with
+  | inl h' =>
+    simp [subNatNat_of_lt h', sub_one_add_one_eq_of_pos (Nat.sub_pos_of_lt h')]
+    conv => lhs; rw [← Nat.sub_add_cancel (Nat.le_of_lt h')]
+    apply subNatNat_add_add
+  | inr h' => simp [subNatNat_of_le h',
+      subNatNat_of_le (Nat.le_trans h' (le_add_left ..)), Nat.add_sub_assoc h']
+
+theorem subNatNat_add_negSucc (m n k : Nat) :
+    subNatNat m n + -[k+1] = subNatNat m (n + succ k) := by
+  have h := Nat.lt_or_ge m n
+  cases h with
+  | inr h' =>
+    rw [subNatNat_of_le h']
+    simp
+    rw [subNatNat_sub h', Nat.add_comm]
+  | inl h' =>
+    have h₂ : m < n + succ k := Nat.lt_of_lt_of_le h' (le_add_right _ _)
+    rw [subNatNat_of_lt h', subNatNat_of_lt h₂]
+    simp only [pred_eq_sub_one, negSucc_add_negSucc, succ_eq_add_one, negSucc.injEq]
+    rw [Nat.add_right_comm, sub_one_add_one_eq_of_pos (Nat.sub_pos_of_lt h'), Nat.sub_sub,
+      ← Nat.add_assoc, succ_sub_succ_eq_sub, Nat.add_comm n,Nat.add_sub_assoc (Nat.le_of_lt h'),
+      Nat.add_comm]
+
+protected theorem add_assoc : ∀ a b c : Int, a + b + c = a + (b + c)
+  | (m:Nat), (n:Nat), c => aux1 ..
+  | Nat.cast m, b, Nat.cast k => by
+    rw [Int.add_comm, ← aux1, Int.add_comm k, aux1, Int.add_comm b]
+  | a, (n:Nat), (k:Nat) => by
+    rw [Int.add_comm, Int.add_comm a, ← aux1, Int.add_comm a, Int.add_comm k]
+  | -[m+1], -[n+1], (k:Nat) => aux2 ..
+  | -[m+1], (n:Nat), -[k+1] => by
+    rw [Int.add_comm, ← aux2, Int.add_comm n, ← aux2, Int.add_comm -[m+1]]
+  | (m:Nat), -[n+1], -[k+1] => by
+    rw [Int.add_comm, Int.add_comm m, Int.add_comm m, ← aux2, Int.add_comm -[k+1]]
+  | -[m+1], -[n+1], -[k+1] => by
+    simp [Nat.add_comm, Nat.add_left_comm, Nat.add_assoc]
+where
+  aux1 (m n : Nat) : ∀ c : Int, m + n + c = m + (n + c)
+    | (k:Nat) => by simp [Nat.add_assoc]
+    | -[k+1]  => by simp [subNatNat_add]
+  aux2 (m n k : Nat) : -[m+1] + -[n+1] + k = -[m+1] + (-[n+1] + k) := by
+    simp
+    rw [Int.add_comm, subNatNat_add_negSucc]
+    simp [Nat.add_comm, Nat.add_left_comm, Nat.add_assoc]
+
+protected theorem add_left_comm (a b c : Int) : a + (b + c) = b + (a + c) := by
+  rw [← Int.add_assoc, Int.add_comm a, Int.add_assoc]
+
+protected theorem add_right_comm (a b c : Int) : a + b + c = a + c + b := by
+  rw [Int.add_assoc, Int.add_comm b, ← Int.add_assoc]
+
+/- ## negation -/
+
+theorem subNatNat_self : ∀ n, subNatNat n n = 0
+  | 0      => rfl
+  | succ m => by rw [subNatNat_of_sub_eq_zero (Nat.sub_self ..), Nat.sub_self, ofNat_zero]
+
+attribute [local simp] subNatNat_self
+
+@[local simp] protected theorem add_left_neg : ∀ a : Int, -a + a = 0
+  | 0      => rfl
+  | succ m => by simp
+  | -[m+1] => by simp
+
+@[local simp] protected theorem add_right_neg (a : Int) : a + -a = 0 := by
+  rw [Int.add_comm, Int.add_left_neg]
+
+@[simp] protected theorem neg_eq_of_add_eq_zero {a b : Int} (h : a + b = 0) : -a = b := by
+  rw [← Int.add_zero (-a), ← h, ← Int.add_assoc, Int.add_left_neg, Int.zero_add]
+
+protected theorem eq_neg_of_eq_neg {a b : Int} (h : a = -b) : b = -a := by
+  rw [h, Int.neg_neg]
+
+protected theorem eq_neg_comm {a b : Int} : a = -b ↔ b = -a :=
+  ⟨Int.eq_neg_of_eq_neg, Int.eq_neg_of_eq_neg⟩
+
+protected theorem neg_eq_comm {a b : Int} : -a = b ↔ -b = a := by
+  rw [eq_comm, Int.eq_neg_comm, eq_comm]
+
+protected theorem neg_add_cancel_left (a b : Int) : -a + (a + b) = b := by
+  rw [← Int.add_assoc, Int.add_left_neg, Int.zero_add]
+
+protected theorem add_neg_cancel_left (a b : Int) : a + (-a + b) = b := by
+  rw [← Int.add_assoc, Int.add_right_neg, Int.zero_add]
+
+protected theorem add_neg_cancel_right (a b : Int) : a + b + -b = a := by
+  rw [Int.add_assoc, Int.add_right_neg, Int.add_zero]
+
+protected theorem neg_add_cancel_right (a b : Int) : a + -b + b = a := by
+  rw [Int.add_assoc, Int.add_left_neg, Int.add_zero]
+
+protected theorem add_left_cancel {a b c : Int} (h : a + b = a + c) : b = c := by
+  have h₁ : -a + (a + b) = -a + (a + c) := by rw [h]
+  simp [← Int.add_assoc, Int.add_left_neg, Int.zero_add] at h₁; exact h₁
+
+@[local simp] protected theorem neg_add {a b : Int} : -(a + b) = -a + -b := by
+  apply Int.add_left_cancel (a := a + b)
+  rw [Int.add_right_neg, Int.add_comm a, ← Int.add_assoc, Int.add_assoc b,
+    Int.add_right_neg, Int.add_zero, Int.add_right_neg]
+
+/- ## subtraction -/
+
+@[simp] theorem negSucc_sub_one (n : Nat) : -[n+1] - 1 = -[n + 1 +1] := rfl
+
+@[simp] protected theorem sub_self (a : Int) : a - a = 0 := by
+  rw [Int.sub_eq_add_neg, Int.add_right_neg]
+
+@[simp] protected theorem sub_zero (a : Int) : a - 0 = a := by simp [Int.sub_eq_add_neg]
+
+@[simp] protected theorem zero_sub (a : Int) : 0 - a = -a := by simp [Int.sub_eq_add_neg]
+
+protected theorem sub_eq_zero_of_eq {a b : Int} (h : a = b) : a - b = 0 := by
+  rw [h, Int.sub_self]
+
+protected theorem eq_of_sub_eq_zero {a b : Int} (h : a - b = 0) : a = b := by
+  have : 0 + b = b := by rw [Int.zero_add]
+  have : a - b + b = b := by rwa [h]
+  rwa [Int.sub_eq_add_neg, Int.neg_add_cancel_right] at this
+
+protected theorem sub_eq_zero {a b : Int} : a - b = 0 ↔ a = b :=
+  ⟨Int.eq_of_sub_eq_zero, Int.sub_eq_zero_of_eq⟩
+
+protected theorem sub_sub (a b c : Int) : a - b - c = a - (b + c) := by
+  simp [Int.sub_eq_add_neg, Int.add_assoc]
+
+protected theorem neg_sub (a b : Int) : -(a - b) = b - a := by
+  simp [Int.sub_eq_add_neg, Int.add_comm]
+
+protected theorem sub_sub_self (a b : Int) : a - (a - b) = b := by
+  simp [Int.sub_eq_add_neg, ← Int.add_assoc]
+
+protected theorem sub_neg (a b : Int) : a - -b = a + b := by simp [Int.sub_eq_add_neg]
+
+@[simp] protected theorem sub_add_cancel (a b : Int) : a - b + b = a :=
+  Int.neg_add_cancel_right a b
+
+@[simp] protected theorem add_sub_cancel (a b : Int) : a + b - b = a :=
+  Int.add_neg_cancel_right a b
+
+protected theorem add_sub_assoc (a b c : Int) : a + b - c = a + (b - c) := by
+  rw [Int.sub_eq_add_neg, Int.add_assoc, ← Int.sub_eq_add_neg]
+
+@[norm_cast] theorem ofNat_sub (h : m ≤ n) : ((n - m : Nat) : Int) = n - m := by
+  match m with
+  | 0 => rfl
+  | succ m =>
+    show ofNat (n - succ m) = subNatNat n (succ m)
+    rw [subNatNat, Nat.sub_eq_zero_of_le h]
+
+theorem negSucc_coe' (n : Nat) : -[n+1] = -↑n - 1 := by
+  rw [Int.sub_eq_add_neg, ← Int.neg_add]; rfl
+
+protected theorem subNatNat_eq_coe {m n : Nat} : subNatNat m n = ↑m - ↑n := by
+  apply subNatNat_elim m n fun m n i => i = m - n
+  · intros i n
+    rw [Int.ofNat_add, Int.sub_eq_add_neg, Int.add_assoc, Int.add_left_comm,
+      Int.add_right_neg, Int.add_zero]
+  · intros i n
+    simp only [negSucc_coe, ofNat_add, Int.sub_eq_add_neg, Int.neg_add, ← Int.add_assoc]
+    rw [← @Int.sub_eq_add_neg n, ← ofNat_sub, Nat.sub_self, ofNat_zero, Int.zero_add]
+    apply Nat.le_refl
+
+theorem toNat_sub (m n : Nat) : toNat (m - n) = m - n := by
+  rw [← Int.subNatNat_eq_coe]
+  refine subNatNat_elim m n (fun m n i => toNat i = m - n) (fun i n => ?_) (fun i n => ?_)
+  · exact (Nat.add_sub_cancel_left ..).symm
+  · dsimp; rw [Nat.add_assoc, Nat.sub_eq_zero_of_le (Nat.le_add_right ..)]; rfl
+
+/- ## add/sub injectivity -/
+
+@[simp]
+protected theorem add_right_inj (i j k : Int) : (i + k = j + k) ↔ i = j := by
+  apply Iff.intro
+  · intro p
+    rw [←Int.add_sub_cancel i k, ←Int.add_sub_cancel j k, p]
+  · exact congrArg (· + k)
+
+@[simp]
+protected theorem add_left_inj (i j k : Int) : (k + i = k + j) ↔ i = j := by
+  simp [Int.add_comm k]
+
+@[simp]
+protected theorem sub_left_inj (i j k : Int) : (k - i = k - j) ↔ i = j := by
+  simp [Int.sub_eq_add_neg, Int.neg_inj]
+
+@[simp]
+protected theorem sub_right_inj (i j k : Int) : (i - k = j - k) ↔ i = j := by
+  simp [Int.sub_eq_add_neg]
+
+/- ## Ring properties -/
+
+@[simp] theorem ofNat_mul_negSucc (m n : Nat) : (m : Int) * -[n+1] = -↑(m * succ n) := rfl
+
+@[simp] theorem negSucc_mul_ofNat (m n : Nat) : -[m+1] * n = -↑(succ m * n) := rfl
+
+@[simp] theorem negSucc_mul_negSucc (m n : Nat) : -[m+1] * -[n+1] = succ m * succ n := rfl
+
+protected theorem mul_comm (a b : Int) : a * b = b * a := by
+  cases a <;> cases b <;> simp [Nat.mul_comm]
+
+theorem ofNat_mul_negOfNat (m n : Nat) : (m : Nat) * negOfNat n = negOfNat (m * n) := by
+  cases n <;> rfl
+
+theorem negOfNat_mul_ofNat (m n : Nat) : negOfNat m * (n : Nat) = negOfNat (m * n) := by
+  rw [Int.mul_comm]; simp [ofNat_mul_negOfNat, Nat.mul_comm]
+
+theorem negSucc_mul_negOfNat (m n : Nat) : -[m+1] * negOfNat n = ofNat (succ m * n) := by
+  cases n <;> rfl
+
+theorem negOfNat_mul_negSucc (m n : Nat) : negOfNat n * -[m+1] = ofNat (n * succ m) := by
+  rw [Int.mul_comm, negSucc_mul_negOfNat, Nat.mul_comm]
+
+attribute [local simp] ofNat_mul_negOfNat negOfNat_mul_ofNat
+  negSucc_mul_negOfNat negOfNat_mul_negSucc
+
+protected theorem mul_assoc (a b c : Int) : a * b * c = a * (b * c) := by
+  cases a <;> cases b <;> cases c <;> simp [Nat.mul_assoc]
+
+protected theorem mul_left_comm (a b c : Int) : a * (b * c) = b * (a * c) := by
+  rw [← Int.mul_assoc, ← Int.mul_assoc, Int.mul_comm a]
+
+protected theorem mul_right_comm (a b c : Int) : a * b * c = a * c * b := by
+  rw [Int.mul_assoc, Int.mul_assoc, Int.mul_comm b]
+
+@[simp] protected theorem mul_zero (a : Int) : a * 0 = 0 := by cases a <;> rfl
+
+@[simp] protected theorem zero_mul (a : Int) : 0 * a = 0 := Int.mul_comm .. ▸ a.mul_zero
+
+theorem negOfNat_eq_subNatNat_zero (n) : negOfNat n = subNatNat 0 n := by cases n <;> rfl
+
+theorem ofNat_mul_subNatNat (m n k : Nat) :
+    m * subNatNat n k = subNatNat (m * n) (m * k) := by
+  cases m with
+  | zero => simp [ofNat_zero, Int.zero_mul, Nat.zero_mul]
+  | succ m => cases n.lt_or_ge k with
+    | inl h =>
+      have h' : succ m * n < succ m * k := Nat.mul_lt_mul_of_pos_left h (Nat.succ_pos m)
+      simp [subNatNat_of_lt h, subNatNat_of_lt h']
+      rw [sub_one_add_one_eq_of_pos (Nat.sub_pos_of_lt h), ← neg_ofNat_succ, Nat.mul_sub_left_distrib,
+        ← succ_pred_eq_of_pos (Nat.sub_pos_of_lt h')]; rfl
+    | inr h =>
+      have h' : succ m * k ≤ succ m * n := Nat.mul_le_mul_left _ h
+      simp [subNatNat_of_le h, subNatNat_of_le h', Nat.mul_sub_left_distrib]
+
+theorem negOfNat_add (m n : Nat) : negOfNat m + negOfNat n = negOfNat (m + n) := by
+  cases m <;> cases n <;> simp [Nat.succ_add] <;> rfl
+
+theorem negSucc_mul_subNatNat (m n k : Nat) :
+    -[m+1] * subNatNat n k = subNatNat (succ m * k) (succ m * n) := by
+  cases n.lt_or_ge k with
+  | inl h =>
+    have h' : succ m * n < succ m * k := Nat.mul_lt_mul_of_pos_left h (Nat.succ_pos m)
+    rw [subNatNat_of_lt h, subNatNat_of_le (Nat.le_of_lt h')]
+    simp [sub_one_add_one_eq_of_pos (Nat.sub_pos_of_lt h), Nat.mul_sub_left_distrib]
+  | inr h => cases Nat.lt_or_ge k n with
+    | inl h' =>
+      have h₁ : succ m * n > succ m * k := Nat.mul_lt_mul_of_pos_left h' (Nat.succ_pos m)
+      rw [subNatNat_of_le h, subNatNat_of_lt h₁, negSucc_mul_ofNat,
+        Nat.mul_sub_left_distrib, ← succ_pred_eq_of_pos (Nat.sub_pos_of_lt h₁)]; rfl
+    | inr h' => rw [Nat.le_antisymm h h', subNatNat_self, subNatNat_self, Int.mul_zero]
+
+attribute [local simp] ofNat_mul_subNatNat negOfNat_add negSucc_mul_subNatNat
+
+protected theorem mul_add : ∀ a b c : Int, a * (b + c) = a * b + a * c
+  | (m:Nat), (n:Nat), (k:Nat) => by simp [Nat.left_distrib]
+  | (m:Nat), (n:Nat), -[k+1]  => by
+    simp [negOfNat_eq_subNatNat_zero]; rw [← subNatNat_add]; rfl
+  | (m:Nat), -[n+1],  (k:Nat) => by
+    simp [negOfNat_eq_subNatNat_zero]; rw [Int.add_comm, ← subNatNat_add]; rfl
+  | (m:Nat), -[n+1],  -[k+1]  => by simp [← Nat.left_distrib, Nat.add_left_comm, Nat.add_assoc]
+  | -[m+1],  (n:Nat), (k:Nat) => by simp [Nat.mul_comm]; rw [← Nat.right_distrib, Nat.mul_comm]
+  | -[m+1],  (n:Nat), -[k+1]  => by
+    simp [negOfNat_eq_subNatNat_zero]; rw [Int.add_comm, ← subNatNat_add]; rfl
+  | -[m+1],  -[n+1],  (k:Nat) => by simp [negOfNat_eq_subNatNat_zero]; rw [← subNatNat_add]; rfl
+  | -[m+1],  -[n+1],  -[k+1]  => by simp [← Nat.left_distrib, Nat.add_left_comm, Nat.add_assoc]
+
+protected theorem add_mul (a b c : Int) : (a + b) * c = a * c + b * c := by
+  simp [Int.mul_comm, Int.mul_add]
+
+protected theorem neg_mul_eq_neg_mul (a b : Int) : -(a * b) = -a * b :=
+  Int.neg_eq_of_add_eq_zero <| by rw [← Int.add_mul, Int.add_right_neg, Int.zero_mul]
+
+protected theorem neg_mul_eq_mul_neg (a b : Int) : -(a * b) = a * -b :=
+  Int.neg_eq_of_add_eq_zero <| by rw [← Int.mul_add, Int.add_right_neg, Int.mul_zero]
+
+@[local simp] protected theorem neg_mul (a b : Int) : -a * b = -(a * b) :=
+  (Int.neg_mul_eq_neg_mul a b).symm
+
+@[local simp] protected theorem mul_neg (a b : Int) : a * -b = -(a * b) :=
+  (Int.neg_mul_eq_mul_neg a b).symm
+
+protected theorem neg_mul_neg (a b : Int) : -a * -b = a * b := by simp
+
+protected theorem neg_mul_comm (a b : Int) : -a * b = a * -b := by simp
+
+protected theorem mul_sub (a b c : Int) : a * (b - c) = a * b - a * c := by
+  simp [Int.sub_eq_add_neg, Int.mul_add]
+
+protected theorem sub_mul (a b c : Int) : (a - b) * c = a * c - b * c := by
+  simp [Int.sub_eq_add_neg, Int.add_mul]
+
+@[simp] protected theorem one_mul : ∀ a : Int, 1 * a = a
+  | ofNat n => show ofNat (1 * n) = ofNat n by rw [Nat.one_mul]
+  | -[n+1]  => show -[1 * n +1] = -[n+1] by rw [Nat.one_mul]
+
+@[simp] protected theorem mul_one (a : Int) : a * 1 = a := by rw [Int.mul_comm, Int.one_mul]
+
+protected theorem mul_neg_one (a : Int) : a * -1 = -a := by rw [Int.mul_neg, Int.mul_one]
+
+protected theorem neg_eq_neg_one_mul : ∀ a : Int, -a = -1 * a
+  | 0      => rfl
+  | succ n => show _ = -[1 * n +1] by rw [Nat.one_mul]; rfl
+  | -[n+1] => show _ = ofNat _ by rw [Nat.one_mul]; rfl
+
+protected theorem mul_eq_zero {a b : Int} : a * b = 0 ↔ a = 0 ∨ b = 0 := by
+  refine ⟨fun h => ?_, fun h => h.elim (by simp [·, Int.zero_mul]) (by simp [·, Int.mul_zero])⟩
+  exact match a, b, h with
+  | .ofNat 0, _, _ => by simp
+  | _, .ofNat 0, _ => by simp
+  | .ofNat (a+1), .negSucc b, h => by cases h
+
+protected theorem mul_ne_zero {a b : Int} (a0 : a ≠ 0) (b0 : b ≠ 0) : a * b ≠ 0 :=
+  Or.rec a0 b0 ∘ Int.mul_eq_zero.mp
+
+protected theorem eq_of_mul_eq_mul_right {a b c : Int} (ha : a ≠ 0) (h : b * a = c * a) : b = c :=
+  have : (b - c) * a = 0 := by rwa [Int.sub_mul, Int.sub_eq_zero]
+  Int.sub_eq_zero.1 <| (Int.mul_eq_zero.mp this).resolve_right ha
+
+protected theorem eq_of_mul_eq_mul_left {a b c : Int} (ha : a ≠ 0) (h : a * b = a * c) : b = c :=
+  have : a * b - a * c = 0 := Int.sub_eq_zero_of_eq h
+  have : a * (b - c) = 0 := by rw [Int.mul_sub, this]
+  have : b - c = 0 := (Int.mul_eq_zero.1 this).resolve_left ha
+  Int.eq_of_sub_eq_zero this
+
+theorem mul_eq_mul_left_iff {a b c : Int} (h : c ≠ 0) : c * a = c * b ↔ a = b :=
+  ⟨Int.eq_of_mul_eq_mul_left h, fun w => congrArg (fun x => c * x) w⟩
+
+theorem mul_eq_mul_right_iff {a b c : Int} (h : c ≠ 0) : a * c = b * c ↔ a = b :=
+  ⟨Int.eq_of_mul_eq_mul_right h, fun w => congrArg (fun x => x * c) w⟩
+
+theorem eq_one_of_mul_eq_self_left {a b : Int} (Hpos : a ≠ 0) (H : b * a = a) : b = 1 :=
+  Int.eq_of_mul_eq_mul_right Hpos <| by rw [Int.one_mul, H]
+
+theorem eq_one_of_mul_eq_self_right {a b : Int} (Hpos : b ≠ 0) (H : b * a = b) : a = 1 :=
+  Int.eq_of_mul_eq_mul_left Hpos <| by rw [Int.mul_one, H]
+
+/-! NatCast lemmas -/
+
+/-!
+The following lemmas are later subsumed by e.g. `Nat.cast_add` and `Nat.cast_mul` in Mathlib
+but it is convenient to have these earlier, for users who only need `Nat` and `Int`.
+-/
+
+theorem natCast_zero : ((0 : Nat) : Int) = (0 : Int) := rfl
+
+theorem natCast_one : ((1 : Nat) : Int) = (1 : Int) := rfl
+
+@[simp] theorem natCast_add (a b : Nat) : ((a + b : Nat) : Int) = (a : Int) + (b : Int) := by
+  -- Note this only works because of local simp attributes in this file,
+  -- so it still makes sense to tag the lemmas with `@[simp]`.
+  simp
+
+@[simp] theorem natCast_mul (a b : Nat) : ((a * b : Nat) : Int) = (a : Int) * (b : Int) := by
+  simp
+
+end Int

src/Init/Data/Int/Pow.lean

@@ -0,0 +1,44 @@
+/-
+Copyright (c) 2016 Jeremy Avigad. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Jeremy Avigad, Deniz Aydin, Floris van Doorn, Mario Carneiro
+-/
+prelude
+import Init.Data.Int.Lemmas
+
+namespace Int
+
+/-! # pow -/
+
+protected theorem pow_zero (b : Int) : b^0 = 1 := rfl
+
+protected theorem pow_succ (b : Int) (e : Nat) : b ^ (e+1) = (b ^ e) * b := rfl
+protected theorem pow_succ' (b : Int) (e : Nat) : b ^ (e+1) = b * (b ^ e) := by
+  rw [Int.mul_comm, Int.pow_succ]
+
+theorem pow_le_pow_of_le_left {n m : Nat} (h : n ≤ m) : ∀ (i : Nat), n^i ≤ m^i
+  | 0      => Nat.le_refl _
+  | i + 1 => Nat.mul_le_mul (pow_le_pow_of_le_left h i) h
+
+theorem pow_le_pow_of_le_right {n : Nat} (hx : n > 0) {i : Nat} : ∀ {j}, i ≤ j → n^i ≤ n^j
+  | 0,      h =>
+    have : i = 0 := Nat.eq_zero_of_le_zero h
+    this.symm ▸ Nat.le_refl _
+  | j + 1, h =>
+    match Nat.le_or_eq_of_le_succ h with
+    | Or.inl h => show n^i ≤ n^j * n from
+      have : n^i * 1 ≤ n^j * n := Nat.mul_le_mul (pow_le_pow_of_le_right hx h) hx
+      Nat.mul_one (n^i) ▸ this
+    | Or.inr h =>
+      h.symm ▸ Nat.le_refl _
+
+theorem pos_pow_of_pos {n : Nat} (m : Nat) (h : 0 < n) : 0 < n^m :=
+  pow_le_pow_of_le_right h (Nat.zero_le _)
+
+theorem natCast_pow (b n : Nat) : ((b^n : Nat) : Int) = (b : Int) ^ n := by
+  match n with
+  | 0 => rfl
+  | n + 1 =>
+    simp only [Nat.pow_succ, Int.pow_succ, natCast_mul, natCast_pow _ n]
+
+end Int

src/Init/Data/List.lean

@@ -7,3 +7,5 @@ prelude
 import Init.Data.List.Basic
 import Init.Data.List.BasicAux
 import Init.Data.List.Control
+import Init.Data.List.Lemmas
+import Init.Data.List.Impl

src/Init/Data/List/Basic.lean

@@ -7,6 +7,7 @@ prelude
 import Init.SimpLemmas
 import Init.Data.Nat.Basic
 import Init.Data.Nat.Div
+
 set_option linter.missingDocs true -- keep it documented
 open Decidable List
 
@@ -54,15 +55,6 @@ variable {α : Type u} {β : Type v} {γ : Type w}
 
 namespace List
 
-instance : GetElem (List α) Nat α fun as i => i < as.length where
-  getElem as i h := as.get ⟨i, h⟩
-
-@[simp] theorem cons_getElem_zero (a : α) (as : List α) (h : 0 < (a :: as).length) : getElem (a :: as) 0 h = a := by
-  rfl
-
-@[simp] theorem cons_getElem_succ (a : α) (as : List α) (i : Nat) (h : i + 1 < (a :: as).length) : getElem (a :: as) (i+1) h = getElem as i (Nat.lt_of_succ_lt_succ h) := by
-  rfl
-
 theorem length_add_eq_lengthTRAux (as : List α) (n : Nat) : as.length + n = as.lengthTRAux n := by
   induction as generalizing n with
   | nil  => simp [length, lengthTRAux]
@@ -458,7 +450,7 @@ contains the longest initial segment for which `p` returns true
 and the second part is everything else.
 
 * `span (· > 5) [6, 8, 9, 5, 2, 9] = ([6, 8, 9], [5, 2, 9])`
-* `span (· > 10) [6, 8, 9, 5, 2, 9] = ([6, 8, 9, 5, 2, 9], [])`
+* `span (· > 10) [6, 8, 9, 5, 2, 9] = ([], [6, 8, 9, 5, 2, 9])`
 -/
 @[inline] def span (p : α → Bool) (as : List α) : List α × List α :=
   loop as []
@@ -520,11 +512,6 @@ def drop : Nat → List α → List α
 @[simp] theorem drop_nil : ([] : List α).drop i = [] := by
   cases i <;> rfl
 
-theorem get_drop_eq_drop (as : List α) (i : Nat) (h : i < as.length) : as[i] :: as.drop (i+1) = as.drop i :=
-  match as, i with
-  | _::_, 0   => rfl
-  | _::_, i+1 => get_drop_eq_drop _ i _
-
 /--
 `O(min n |xs|)`. Returns the first `n` elements of `xs`, or the whole list if `n` is too large.
 * `take 0 [a, b, c, d, e] = []`
@@ -603,6 +590,27 @@ The longer list is truncated to match the shorter list.
 def zip : List α → List β → List (Prod α β) :=
   zipWith Prod.mk
 
+/--
+`O(max |xs| |ys|)`.
+Version of `List.zipWith` that continues to the end of both lists,
+passing `none` to one argument once the shorter list has run out.
+-/
+def zipWithAll (f : Option α → Option β → γ) : List α → List β → List γ
+  | [], bs => bs.map fun b => f none (some b)
+  | a :: as, [] => (a :: as).map fun a => f (some a) none
+  | a :: as, b :: bs => f a b :: zipWithAll f as bs
+
+@[simp] theorem zipWithAll_nil_right :
+    zipWithAll f as [] = as.map fun a => f (some a) none := by
+  cases as <;> rfl
+
+@[simp] theorem zipWithAll_nil_left :
+    zipWithAll f [] bs = bs.map fun b => f none (some b) := by
+  rfl
+
+@[simp] theorem zipWithAll_cons_cons :
+    zipWithAll f (a :: as) (b :: bs) = f (some a) (some b) :: zipWithAll f as bs := rfl
+
 /--
 `O(|l|)`. Separates a list of pairs into two lists containing the first components and second components.
 * `unzip [(x₁, y₁), (x₂, y₂), (x₃, y₃)] = ([x₁, x₂, x₃], [y₁, y₂, y₃])`
@@ -706,9 +714,9 @@ inductive lt [LT α] : List α → List α → Prop where
 instance [LT α] : LT (List α) := ⟨List.lt⟩
 
 instance hasDecidableLt [LT α] [h : DecidableRel (α:=α) (·<·)] : (l₁ l₂ : List α) → Decidable (l₁ < l₂)
-  | [],    []    => isFalse (fun h => nomatch h)
+  | [],    []    => isFalse nofun
   | [],    _::_  => isTrue (List.lt.nil _ _)
-  | _::_, []     => isFalse (fun h => nomatch h)
+  | _::_, []     => isFalse nofun
   | a::as, b::bs =>
     match h a b with
     | isTrue h₁  => isTrue (List.lt.head _ _ h₁)
@@ -868,6 +876,33 @@ def minimum? [Min α] : List α → Option α
   | []    => none
   | a::as => some <| as.foldl min a
 
+/-- Inserts an element into a list without duplication. -/
+@[inline] protected def insert [BEq α] (a : α) (l : List α) : List α :=
+  if l.elem a then l else a :: l
+
+instance decidableBEx (p : α → Prop) [DecidablePred p] :
+    ∀ l : List α, Decidable (Exists fun x => x ∈ l ∧ p x)
+  | [] => isFalse nofun
+  | x :: xs =>
+    if h₁ : p x then isTrue ⟨x, .head .., h₁⟩ else
+      match decidableBEx p xs with
+      | isTrue h₂ => isTrue <| let ⟨y, hm, hp⟩ := h₂; ⟨y, .tail _ hm, hp⟩
+      | isFalse h₂ => isFalse fun
+        | ⟨y, .tail _ h, hp⟩ => h₂ ⟨y, h, hp⟩
+        | ⟨_, .head .., hp⟩ => h₁ hp
+
+instance decidableBAll (p : α → Prop) [DecidablePred p] :
+    ∀ l : List α, Decidable (∀ x, x ∈ l → p x)
+  | [] => isTrue nofun
+  | x :: xs =>
+    if h₁ : p x then
+      match decidableBAll p xs with
+      | isTrue h₂ => isTrue fun
+        | y, .tail _ h => h₂ y h
+        | _, .head .. => h₁
+      | isFalse h₂ => isFalse fun H => h₂ fun y hm => H y (.tail _ hm)
+    else isFalse fun H => h₁ <| H x (.head ..)
+
 instance [BEq α] [LawfulBEq α] : LawfulBEq (List α) where
   eq_of_beq {as bs} := by
     induction as generalizing bs with
@@ -876,7 +911,7 @@ instance [BEq α] [LawfulBEq α] : LawfulBEq (List α) where
       cases bs with
       | nil => intro h; contradiction
       | cons b bs =>
-        simp [show (a::as == b::bs) = (a == b && as == bs) from rfl]
+        simp [show (a::as == b::bs) = (a == b && as == bs) from rfl, -and_imp]
         intro ⟨h₁, h₂⟩
         exact ⟨h₁, ih h₂⟩
   rfl {as} := by

src/Init/Data/List/BasicAux.lean

@@ -5,8 +5,6 @@ Author: Leonardo de Moura
 -/
 prelude
 import Init.Data.Nat.Linear
-import Init.Data.List.Basic
-import Init.Util
 
 universe u
 
@@ -14,60 +12,139 @@ namespace List
 /-! The following functions can't be defined at `Init.Data.List.Basic`, because they depend on `Init.Util`,
    and `Init.Util` depends on `Init.Data.List.Basic`. -/
 
-def get! [Inhabited α] : List α → Nat → α
+/--
+Returns the `i`-th element in the list (zero-based).
+
+If the index is out of bounds (`i ≥ as.length`), this function panics when executed, and returns
+`default`. See `get?` and `getD` for safer alternatives.
+-/
+def get! [Inhabited α] : (as : List α) → (i : Nat) → α
   | a::_,  0   => a
   | _::as, n+1 => get! as n
   | _,     _   => panic! "invalid index"
 
-def get? : List α → Nat → Option α
+/--
+Returns the `i`-th element in the list (zero-based).
+
+If the index is out of bounds (`i ≥ as.length`), this function returns `none`.
+Also see `get`, `getD` and `get!`.
+-/
+def get? : (as : List α) → (i : Nat) → Option α
   | a::_,  0   => some a
   | _::as, n+1 => get? as n
   | _,     _   => none
 
-def getD (as : List α) (idx : Nat) (a₀ : α) : α :=
-  (as.get? idx).getD a₀
+/--
+Returns the `i`-th element in the list (zero-based).
 
+If the index is out of bounds (`i ≥ as.length`), this function returns `fallback`.
+See also `get?` and `get!`.
+-/
+def getD (as : List α) (i : Nat) (fallback : α) : α :=
+  (as.get? i).getD fallback
+
+/--
+Returns the first element in the list.
+
+If the list is empty, this function panics when executed, and returns `default`.
+See `head` and `headD` for safer alternatives.
+-/
 def head! [Inhabited α] : List α → α
   | []   => panic! "empty list"
   | a::_ => a
 
+/--
+Returns the first element in the list.
+
+If the list is empty, this function returns `none`.
+Also see `headD` and `head!`.
+-/
 def head? : List α → Option α
   | []   => none
   | a::_ => some a
 
-def headD : List α → α → α
-  | [],   a₀ => a₀
+/--
+Returns the first element in the list.
+
+If the list is empty, this function returns `fallback`.
+Also see `head?` and `head!`.
+-/
+def headD : (as : List α) → (fallback : α) → α
+  | [],   fallback => fallback
   | a::_, _  => a
 
+/--
+Returns the first element of a non-empty list.
+-/
 def head : (as : List α) → as ≠ [] → α
   | a::_, _ => a
 
+/--
+Drops the first element of the list.
+
+If the list is empty, this function panics when executed, and returns the empty list.
+See `tail` and `tailD` for safer alternatives.
+-/
 def tail! : List α → List α
   | []    => panic! "empty list"
   | _::as => as
 
+/--
+Drops the first element of the list.
+
+If the list is empty, this function returns `none`.
+Also see `tailD` and `tail!`.
+-/
 def tail? : List α → Option (List α)
   | []    => none
   | _::as => some as
 
-def tailD : List α → List α → List α
-  | [],   as₀ => as₀
-  | _::as, _  => as
+/--
+Drops the first element of the list.
 
+If the list is empty, this function returns `fallback`.
+Also see `head?` and `head!`.
+-/
+def tailD (list fallback : List α) : List α :=
+  match list with
+  | [] => fallback
+  | _ :: tl => tl
+
+/--
+Returns the last element of a non-empty list.
+-/
 def getLast : ∀ (as : List α), as ≠ [] → α
   | [],       h => absurd rfl h
   | [a],      _ => a
   | _::b::as, _ => getLast (b::as) (fun h => List.noConfusion h)
 
+/--
+Returns the last element in the list.
+
+If the list is empty, this function panics when executed, and returns `default`.
+See `getLast` and `getLastD` for safer alternatives.
+-/
 def getLast! [Inhabited α] : List α → α
   | []    => panic! "empty list"
   | a::as => getLast (a::as) (fun h => List.noConfusion h)
 
+/--
+Returns the last element in the list.
+
+If the list is empty, this function returns `none`.
+Also see `getLastD` and `getLast!`.
+-/
 def getLast? : List α → Option α
   | []    => none
   | a::as => some (getLast (a::as) (fun h => List.noConfusion h))
 
-def getLastD : List α → α → α
+/--
+Returns the last element in the list.
+
+If the list is empty, this function returns `fallback`.
+Also see `getLast?` and `getLast!`.
+-/
+def getLastD : (as : List α) → (fallback : α) → α
   | [],   a₀ => a₀
   | a::as, _ => getLast (a::as) (fun h => List.noConfusion h)
 
@@ -207,4 +284,42 @@ if the result of each `f a` is a pointer equal value `a`.
 def mapMono (as : List α) (f : α → α) : List α :=
   Id.run <| as.mapMonoM f
 
+/--
+Monadic generalization of `List.partition`.
+
+This uses `Array.toList` and which isn't imported by `Init.Data.List.Basic`.
+-/
+@[inline] def partitionM [Monad m] (p : α → m Bool) (l : List α) : m (List α × List α) :=
+  go l #[] #[]
+where
+  /-- Auxiliary for `partitionM`:
+  `partitionM.go p l acc₁ acc₂` returns `(acc₁.toList ++ left, acc₂.toList ++ right)`
+  if `partitionM p l` returns `(left, right)`. -/
+  @[specialize] go : List α → Array α → Array α → m (List α × List α)
+  | [], acc₁, acc₂ => pure (acc₁.toList, acc₂.toList)
+  | x :: xs, acc₁, acc₂ => do
+    if ← p x then
+      go xs (acc₁.push x) acc₂
+    else
+      go xs acc₁ (acc₂.push x)
+
+/--
+Given a function `f : α → β ⊕ γ`, `partitionMap f l` maps the list by `f`
+whilst partitioning the result it into a pair of lists, `List β × List γ`,
+partitioning the `.inl _` into the left list, and the `.inr _` into the right List.
+```
+partitionMap (id : Nat ⊕ Nat → Nat ⊕ Nat) [inl 0, inr 1, inl 2] = ([0, 2], [1])
+```
+-/
+@[inline] def partitionMap (f : α → β ⊕ γ) (l : List α) : List β × List γ := go l #[] #[] where
+  /-- Auxiliary for `partitionMap`:
+  `partitionMap.go f l acc₁ acc₂ = (acc₁.toList ++ left, acc₂.toList ++ right)`
+  if `partitionMap f l = (left, right)`. -/
+  @[specialize] go : List α → Array β → Array γ → List β × List γ
+  | [], acc₁, acc₂ => (acc₁.toList, acc₂.toList)
+  | x :: xs, acc₁, acc₂ =>
+    match f x with
+    | .inl a => go xs (acc₁.push a) acc₂
+    | .inr b => go xs acc₁ (acc₂.push b)
+
 end List

src/Init/Data/List/Control.lean

@@ -40,6 +40,13 @@ Finally, we rarely use `mapM` with something that is not a `Monad`.
 Users that want to use `mapM` with `Applicative` should use `mapA` instead.
 -/
 
+/--
+Applies the monadic action `f` on every element in the list, left-to-right, and returns the list of
+results.
+
+See `List.forM` for the variant that discards the results.
+See `List.mapA` for the variant that works with `Applicative`.
+-/
 @[inline]
 def mapM {m : Type u → Type v} [Monad m] {α : Type w} {β : Type u} (f : α → m β) (as : List α) : m (List β) :=
   let rec @[specialize] loop
@@ -47,17 +54,42 @@ def mapM {m : Type u → Type v} [Monad m] {α : Type w} {β : Type u} (f : α
     | a :: as, bs => do loop as ((← f a)::bs)
   loop as []
 
+/--
+Applies the applicative action `f` on every element in the list, left-to-right, and returns the list of
+results.
+
+NB: If `m` is also a `Monad`, then using `mapM` can be more efficient.
+
+See `List.forA` for the variant that discards the results.
+See `List.mapM` for the variant that works with `Monad`.
+
+**Warning**: this function is not tail-recursive, meaning that it may fail with a stack overflow on long lists.
+-/
 @[specialize]
 def mapA {m : Type u → Type v} [Applicative m] {α : Type w} {β : Type u} (f : α → m β) : List α → m (List β)
   | []    => pure []
   | a::as => List.cons <$> f a <*> mapA f as
 
+/--
+Applies the monadic action `f` on every element in the list, left-to-right.
+
+See `List.mapM` for the variant that collects results.
+See `List.forA` for the variant that works with `Applicative`.
+-/
 @[specialize]
 protected def forM {m : Type u → Type v} [Monad m] {α : Type w} (as : List α) (f : α → m PUnit) : m PUnit :=
   match as with
   | []      => pure ⟨⟩
   | a :: as => do f a; List.forM as f
 
+/--
+Applies the applicative action `f` on every element in the list, left-to-right.
+
+NB: If `m` is also a `Monad`, then using `forM` can be more efficient.
+
+See `List.mapA` for the variant that collects results.
+See `List.forM` for the variant that works with `Monad`.
+-/
 @[specialize]
 def forA {m : Type u → Type v} [Applicative m] {α : Type w} (as : List α) (f : α → m PUnit) : m PUnit :=
   match as with
@@ -71,15 +103,27 @@ def filterAuxM {m : Type → Type v} [Monad m] {α : Type} (f : α → m Bool) :
     let b ← f h
     filterAuxM f t (cond b (h :: acc) acc)
 
+/--
+Applies the monadic predicate `p` on every element in the list, left-to-right, and returns those
+elements `x` for which `p x` returns `true`.
+-/
 @[inline]
-def filterM {m : Type → Type v} [Monad m] {α : Type} (f : α → m Bool) (as : List α) : m (List α) := do
-  let as ← filterAuxM f as []
+def filterM {m : Type → Type v} [Monad m] {α : Type} (p : α → m Bool) (as : List α) : m (List α) := do
+  let as ← filterAuxM p as []
   pure as.reverse
 
+/--
+Applies the monadic predicate `p` on every element in the list, right-to-left, and returns those
+elements `x` for which `p x` returns `true`.
+-/
 @[inline]
-def filterRevM {m : Type → Type v} [Monad m] {α : Type} (f : α → m Bool) (as : List α) : m (List α) :=
-  filterAuxM f as.reverse []
+def filterRevM {m : Type → Type v} [Monad m] {α : Type} (p : α → m Bool) (as : List α) : m (List α) :=
+  filterAuxM p as.reverse []
 
+/--
+Applies the monadic function `f` on every element `x` in the list, left-to-right, and returns those
+results `y` for which `f x` returns `some y`.
+-/
 @[inline]
 def filterMapM {m : Type u → Type v} [Monad m] {α β : Type u} (f : α → m (Option β)) (as : List α) : m (List β) :=
   let rec @[specialize] loop
@@ -90,6 +134,16 @@ def filterMapM {m : Type u → Type v} [Monad m] {α β : Type u} (f : α → m
       | some b => loop as (b::bs)
   loop as.reverse []
 
+/--
+Folds a monadic function over a list from left to right:
+```
+foldlM f x₀ [a, b, c] = do
+  let x₁ ← f x₀ a
+  let x₂ ← f x₁ b
+  let x₃ ← f x₂ c
+  pure x₃
+```
+-/
 @[specialize]
 protected def foldlM {m : Type u → Type v} [Monad m] {s : Type u} {α : Type w} : (f : s → α → m s) → (init : s) → List α → m s
   | _, s, []      => pure s
@@ -97,10 +151,26 @@ protected def foldlM {m : Type u → Type v} [Monad m] {s : Type u} {α : Type w
     let s' ← f s a
     List.foldlM f s' as
 
+/--
+Folds a monadic function over a list from right to left:
+```
+foldrM f x₀ [a, b, c] = do
+  let x₁ ← f c x₀
+  let x₂ ← f b x₁
+  let x₃ ← f a x₂
+  pure x₃
+```
+-/
 @[inline]
 def foldrM {m : Type u → Type v} [Monad m] {s : Type u} {α : Type w} (f : α → s → m s) (init : s) (l : List α) : m s :=
   l.reverse.foldlM (fun s a => f a s) init
 
+/--
+Maps `f` over the list and collects the results with `<|>`.
+```
+firstM f [a, b, c] = f a <|> f b <|> f c <|> failure
+```
+-/
 @[specialize]
 def firstM {m : Type u → Type v} [Alternative m] {α : Type w} {β : Type u} (f : α → m β) : List α → m β
   | []    => failure

src/Init/Data/List/Impl.lean

@@ -0,0 +1,261 @@
+/-
+Copyright (c) 2016 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Leonardo de Moura
+-/
+
+prelude
+import Init.Data.Array.Lemmas
+
+/-!
+## Tail recursive implementations for `List` definitions.
+
+Many of the proofs require theorems about `Array`,
+so these are in a separate file to minimize imports.
+-/
+
+namespace List
+
+/-- Tail recursive version of `erase`. -/
+@[inline] def setTR (l : List α) (n : Nat) (a : α) : List α := go l n #[] where
+  /-- Auxiliary for `setTR`: `setTR.go l a xs n acc = acc.toList ++ set xs a`,
+  unless `n ≥ l.length` in which case it returns `l` -/
+  go : List α → Nat → Array α → List α
+  | [], _, _ => l
+  | _::xs, 0, acc => acc.toListAppend (a::xs)
+  | x::xs, n+1, acc => go xs n (acc.push x)
+
+@[csimp] theorem set_eq_setTR : @set = @setTR := by
+  funext α l n a; simp [setTR]
+  let rec go (acc) : ∀ xs n, l = acc.data ++ xs →
+    setTR.go l a xs n acc = acc.data ++ xs.set n a
+  | [], _ => fun h => by simp [setTR.go, set, h]
+  | x::xs, 0 => by simp [setTR.go, set]
+  | x::xs, n+1 => fun h => by simp [setTR.go, set]; rw [go _ xs]; {simp}; simp [h]
+  exact (go #[] _ _ rfl).symm
+
+/-- Tail recursive version of `erase`. -/
+@[inline] def eraseTR [BEq α] (l : List α) (a : α) : List α := go l #[] where
+  /-- Auxiliary for `eraseTR`: `eraseTR.go l a xs acc = acc.toList ++ erase xs a`,
+  unless `a` is not present in which case it returns `l` -/
+  go : List α → Array α → List α
+  | [], _ => l
+  | x::xs, acc => bif x == a then acc.toListAppend xs else go xs (acc.push x)
+
+@[csimp] theorem erase_eq_eraseTR : @List.erase = @eraseTR := by
+  funext α _ l a; simp [eraseTR]
+  suffices ∀ xs acc, l = acc.data ++ xs → eraseTR.go l a xs acc = acc.data ++ xs.erase a from
+    (this l #[] (by simp)).symm
+  intro xs; induction xs with intro acc h
+  | nil => simp [List.erase, eraseTR.go, h]
+  | cons x xs IH =>
+    simp [List.erase, eraseTR.go]
+    cases x == a <;> simp
+    · rw [IH]; simp; simp; exact h
+
+/-- Tail recursive version of `eraseIdx`. -/
+@[inline] def eraseIdxTR (l : List α) (n : Nat) : List α := go l n #[] where
+  /-- Auxiliary for `eraseIdxTR`: `eraseIdxTR.go l n xs acc = acc.toList ++ eraseIdx xs a`,
+  unless `a` is not present in which case it returns `l` -/
+  go : List α → Nat → Array α → List α
+  | [], _, _ => l
+  | _::as, 0, acc => acc.toListAppend as
+  | a::as, n+1, acc => go as n (acc.push a)
+
+@[csimp] theorem eraseIdx_eq_eraseIdxTR : @eraseIdx = @eraseIdxTR := by
+  funext α l n; simp [eraseIdxTR]
+  suffices ∀ xs acc, l = acc.data ++ xs → eraseIdxTR.go l xs n acc = acc.data ++ xs.eraseIdx n from
+    (this l #[] (by simp)).symm
+  intro xs; induction xs generalizing n with intro acc h
+  | nil => simp [eraseIdx, eraseIdxTR.go, h]
+  | cons x xs IH =>
+    match n with
+    | 0 => simp [eraseIdx, eraseIdxTR.go]
+    | n+1 =>
+      simp [eraseIdx, eraseIdxTR.go]
+      rw [IH]; simp; simp; exact h
+
+/-- Tail recursive version of `bind`. -/
+@[inline] def bindTR (as : List α) (f : α → List β) : List β := go as #[] where
+  /-- Auxiliary for `bind`: `bind.go f as = acc.toList ++ bind f as` -/
+  @[specialize] go : List α → Array β → List β
+  | [], acc => acc.toList
+  | x::xs, acc => go xs (acc ++ f x)
+
+@[csimp] theorem bind_eq_bindTR : @List.bind = @bindTR := by
+  funext α β as f
+  let rec go : ∀ as acc, bindTR.go f as acc = acc.data ++ as.bind f
+    | [], acc => by simp [bindTR.go, bind]
+    | x::xs, acc => by simp [bindTR.go, bind, go xs]
+  exact (go as #[]).symm
+
+/-- Tail recursive version of `join`. -/
+@[inline] def joinTR (l : List (List α)) : List α := bindTR l id
+
+@[csimp] theorem join_eq_joinTR : @join = @joinTR := by
+  funext α l; rw [← List.bind_id, List.bind_eq_bindTR]; rfl
+
+/-- Tail recursive version of `filterMap`. -/
+@[inline] def filterMapTR (f : α → Option β) (l : List α) : List β := go l #[] where
+  /-- Auxiliary for `filterMap`: `filterMap.go f l = acc.toList ++ filterMap f l` -/
+  @[specialize] go : List α → Array β → List β
+  | [], acc => acc.toList
+  | a::as, acc => match f a with
+    | none => go as acc
+    | some b => go as (acc.push b)
+
+@[csimp] theorem filterMap_eq_filterMapTR : @List.filterMap = @filterMapTR := by
+  funext α β f l
+  let rec go : ∀ as acc, filterMapTR.go f as acc = acc.data ++ as.filterMap f
+    | [], acc => by simp [filterMapTR.go, filterMap]
+    | a::as, acc => by simp [filterMapTR.go, filterMap, go as]; split <;> simp [*]
+  exact (go l #[]).symm
+
+/-- Tail recursive version of `replace`. -/
+@[inline] def replaceTR [BEq α] (l : List α) (b c : α) : List α := go l #[] where
+  /-- Auxiliary for `replace`: `replace.go l b c xs acc = acc.toList ++ replace xs b c`,
+  unless `b` is not found in `xs` in which case it returns `l`. -/
+  @[specialize] go : List α → Array α → List α
+  | [], _ => l
+  | a::as, acc => bif a == b then acc.toListAppend (c::as) else go as (acc.push a)
+
+@[csimp] theorem replace_eq_replaceTR : @List.replace = @replaceTR := by
+  funext α _ l b c; simp [replaceTR]
+  suffices ∀ xs acc, l = acc.data ++ xs →
+      replaceTR.go l b c xs acc = acc.data ++ xs.replace b c from
+    (this l #[] (by simp)).symm
+  intro xs; induction xs with intro acc
+  | nil => simp [replace, replaceTR.go]
+  | cons x xs IH =>
+    simp [replace, replaceTR.go]; split <;> simp [*]
+    · intro h; rw [IH]; simp; simp; exact h
+
+/-- Tail recursive version of `take`. -/
+@[inline] def takeTR (n : Nat) (l : List α) : List α := go l n #[] where
+  /-- Auxiliary for `take`: `take.go l xs n acc = acc.toList ++ take n xs`,
+  unless `n ≥ xs.length` in which case it returns `l`. -/
+  @[specialize] go : List α → Nat → Array α → List α
+  | [], _, _ => l
+  | _::_, 0, acc => acc.toList
+  | a::as, n+1, acc => go as n (acc.push a)
+
+@[csimp] theorem take_eq_takeTR : @take = @takeTR := by
+  funext α n l; simp [takeTR]
+  suffices ∀ xs acc, l = acc.data ++ xs → takeTR.go l xs n acc = acc.data ++ xs.take n from
+    (this l #[] (by simp)).symm
+  intro xs; induction xs generalizing n with intro acc
+  | nil => cases n <;> simp [take, takeTR.go]
+  | cons x xs IH =>
+    cases n with simp [take, takeTR.go]
+    | succ n => intro h; rw [IH]; simp; simp; exact h
+
+/-- Tail recursive version of `takeWhile`. -/
+@[inline] def takeWhileTR (p : α → Bool) (l : List α) : List α := go l #[] where
+  /-- Auxiliary for `takeWhile`: `takeWhile.go p l xs acc = acc.toList ++ takeWhile p xs`,
+  unless no element satisfying `p` is found in `xs` in which case it returns `l`. -/
+  @[specialize] go : List α → Array α → List α
+  | [], _ => l
+  | a::as, acc => bif p a then go as (acc.push a) else acc.toList
+
+@[csimp] theorem takeWhile_eq_takeWhileTR : @takeWhile = @takeWhileTR := by
+  funext α p l; simp [takeWhileTR]
+  suffices ∀ xs acc, l = acc.data ++ xs →
+      takeWhileTR.go p l xs acc = acc.data ++ xs.takeWhile p from
+    (this l #[] (by simp)).symm
+  intro xs; induction xs with intro acc
+  | nil => simp [takeWhile, takeWhileTR.go]
+  | cons x xs IH =>
+    simp [takeWhile, takeWhileTR.go]; split <;> simp [*]
+    · intro h; rw [IH]; simp; simp; exact h
+
+/-- Tail recursive version of `foldr`. -/
+@[specialize] def foldrTR (f : α → β → β) (init : β) (l : List α) : β := l.toArray.foldr f init
+
+@[csimp] theorem foldr_eq_foldrTR : @foldr = @foldrTR := by
+  funext α β f init l; simp [foldrTR, Array.foldr_eq_foldr_data, -Array.size_toArray]
+
+/-- Tail recursive version of `zipWith`. -/
+@[inline] def zipWithTR (f : α → β → γ) (as : List α) (bs : List β) : List γ := go as bs #[] where
+  /-- Auxiliary for `zipWith`: `zipWith.go f as bs acc = acc.toList ++ zipWith f as bs` -/
+  go : List α → List β → Array γ → List γ
+  | a::as, b::bs, acc => go as bs (acc.push (f a b))
+  | _, _, acc => acc.toList
+
+@[csimp] theorem zipWith_eq_zipWithTR : @zipWith = @zipWithTR := by
+  funext α β γ f as bs
+  let rec go : ∀ as bs acc, zipWithTR.go f as bs acc = acc.data ++ as.zipWith f bs
+    | [], _, acc | _::_, [], acc => by simp [zipWithTR.go, zipWith]
+    | a::as, b::bs, acc => by simp [zipWithTR.go, zipWith, go as bs]
+  exact (go as bs #[]).symm
+
+/-- Tail recursive version of `unzip`. -/
+def unzipTR (l : List (α × β)) : List α × List β :=
+  l.foldr (fun (a, b) (al, bl) => (a::al, b::bl)) ([], [])
+
+@[csimp] theorem unzip_eq_unzipTR : @unzip = @unzipTR := by
+  funext α β l; simp [unzipTR]; induction l <;> simp [*]
+
+/-- Tail recursive version of `enumFrom`. -/
+def enumFromTR (n : Nat) (l : List α) : List (Nat × α) :=
+  let arr := l.toArray
+  (arr.foldr (fun a (n, acc) => (n-1, (n-1, a) :: acc)) (n + arr.size, [])).2
+
+@[csimp] theorem enumFrom_eq_enumFromTR : @enumFrom = @enumFromTR := by
+  funext α n l; simp [enumFromTR, -Array.size_toArray]
+  let f := fun (a : α) (n, acc) => (n-1, (n-1, a) :: acc)
+  let rec go : ∀ l n, l.foldr f (n + l.length, []) = (n, enumFrom n l)
+    | [], n => rfl
+    | a::as, n => by
+      rw [← show _ + as.length = n + (a::as).length from Nat.succ_add .., foldr, go as]
+      simp [enumFrom, f]
+  rw [Array.foldr_eq_foldr_data]
+  simp [go]
+
+theorem replicateTR_loop_eq : ∀ n, replicateTR.loop a n acc = replicate n a ++ acc
+  | 0 => rfl
+  | n+1 => by rw [← replicateTR_loop_replicate_eq _ 1 n, replicate, replicate,
+    replicateTR.loop, replicateTR_loop_eq n, replicateTR_loop_eq n, append_assoc]; rfl
+
+/-- Tail recursive version of `dropLast`. -/
+@[inline] def dropLastTR (l : List α) : List α := l.toArray.pop.toList
+
+@[csimp] theorem dropLast_eq_dropLastTR : @dropLast = @dropLastTR := by
+  funext α l; simp [dropLastTR]
+
+/-- Tail recursive version of `intersperse`. -/
+def intersperseTR (sep : α) : List α → List α
+  | [] => []
+  | [x] => [x]
+  | x::y::xs => x :: sep :: y :: xs.foldr (fun a r => sep :: a :: r) []
+
+@[csimp] theorem intersperse_eq_intersperseTR : @intersperse = @intersperseTR := by
+  funext α sep l; simp [intersperseTR]
+  match l with
+  | [] | [_] => rfl
+  | x::y::xs => simp [intersperse]; induction xs generalizing y <;> simp [*]
+
+/-- Tail recursive version of `intercalate`. -/
+def intercalateTR (sep : List α) : List (List α) → List α
+  | [] => []
+  | [x] => x
+  | x::xs => go sep.toArray x xs #[]
+where
+  /-- Auxiliary for `intercalateTR`:
+  `intercalateTR.go sep x xs acc = acc.toList ++ intercalate sep.toList (x::xs)` -/
+  go (sep : Array α) : List α → List (List α) → Array α → List α
+  | x, [], acc => acc.toListAppend x
+  | x, y::xs, acc => go sep y xs (acc ++ x ++ sep)
+
+@[csimp] theorem intercalate_eq_intercalateTR : @intercalate = @intercalateTR := by
+  funext α sep l; simp [intercalate, intercalateTR]
+  match l with
+  | [] => rfl
+  | [_] => simp
+  | x::y::xs =>
+    let rec go {acc x} : ∀ xs,
+      intercalateTR.go sep.toArray x xs acc = acc.data ++ join (intersperse sep (x::xs))
+    | [] => by simp [intercalateTR.go]
+    | _::_ => by simp [intercalateTR.go, go]
+    simp [intersperse, go]
+
+end List

src/Init/Data/List/Lemmas.lean

@@ -0,0 +1,717 @@
+/-
+Copyright (c) 2014 Parikshit Khanna. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Parikshit Khanna, Jeremy Avigad, Leonardo de Moura, Floris van Doorn, Mario Carneiro
+-/
+prelude
+import Init.Data.List.BasicAux
+import Init.Data.List.Control
+import Init.PropLemmas
+import Init.Control.Lawful.Basic
+import Init.Hints
+
+namespace List
+
+open Nat
+
+/-!
+# Bootstrapping theorems for lists
+
+These are theorems used in the definitions of `Std.Data.List.Basic` and tactics.
+New theorems should be added to `Std.Data.List.Lemmas` if they are not needed by the bootstrap.
+-/
+
+attribute [simp] concat_eq_append append_assoc
+
+@[simp] theorem get?_nil : @get? α [] n = none := rfl
+@[simp] theorem get?_cons_zero : @get? α (a::l) 0 = some a := rfl
+@[simp] theorem get?_cons_succ : @get? α (a::l) (n+1) = get? l n := rfl
+@[simp] theorem get_cons_zero : get (a::l) (0 : Fin (l.length + 1)) = a := rfl
+@[simp] theorem head?_nil : @head? α [] = none := rfl
+@[simp] theorem head?_cons : @head? α (a::l) = some a := rfl
+@[simp 1100] theorem headD_nil : @headD α [] d = d := rfl
+@[simp 1100] theorem headD_cons : @headD α (a::l) d = a := rfl
+@[simp] theorem head_cons : @head α (a::l) h = a := rfl
+@[simp] theorem tail?_nil : @tail? α [] = none := rfl
+@[simp] theorem tail?_cons : @tail? α (a::l) = some l := rfl
+@[simp] theorem tail!_cons : @tail! α (a::l) = l := rfl
+@[simp 1100] theorem tailD_nil : @tailD α [] l' = l' := rfl
+@[simp 1100] theorem tailD_cons : @tailD α (a::l) l' = l := rfl
+@[simp] theorem any_nil : [].any f = false := rfl
+@[simp] theorem any_cons : (a::l).any f = (f a || l.any f) := rfl
+@[simp] theorem all_nil : [].all f = true := rfl
+@[simp] theorem all_cons : (a::l).all f = (f a && l.all f) := rfl
+@[simp] theorem or_nil : [].or = false := rfl
+@[simp] theorem or_cons : (a::l).or = (a || l.or) := rfl
+@[simp] theorem and_nil : [].and = true := rfl
+@[simp] theorem and_cons : (a::l).and = (a && l.and) := rfl
+
+/-! ### length -/
+
+theorem eq_nil_of_length_eq_zero (_ : length l = 0) : l = [] := match l with | [] => rfl
+
+theorem ne_nil_of_length_eq_succ (_ : length l = succ n) : l ≠ [] := fun _ => nomatch l
+
+theorem length_eq_zero : length l = 0 ↔ l = [] :=
+  ⟨eq_nil_of_length_eq_zero, fun h => h ▸ rfl⟩
+
+/-! ### mem -/
+
+@[simp] theorem not_mem_nil (a : α) : ¬ a ∈ [] := nofun
+
+@[simp] theorem mem_cons : a ∈ (b :: l) ↔ a = b ∨ a ∈ l :=
+  ⟨fun h => by cases h <;> simp [Membership.mem, *],
+   fun | Or.inl rfl => by constructor | Or.inr h => by constructor; assumption⟩
+
+theorem mem_cons_self (a : α) (l : List α) : a ∈ a :: l := .head ..
+
+theorem mem_cons_of_mem (y : α) {a : α} {l : List α} : a ∈ l → a ∈ y :: l := .tail _
+
+theorem eq_nil_iff_forall_not_mem {l : List α} : l = [] ↔ ∀ a, a ∉ l := by
+  cases l <;> simp [-not_or]
+
+/-! ### append -/
+
+@[simp 1100] theorem singleton_append : [x] ++ l = x :: l := rfl
+
+theorem append_inj :
+    ∀ {s₁ s₂ t₁ t₂ : List α}, s₁ ++ t₁ = s₂ ++ t₂ → length s₁ = length s₂ → s₁ = s₂ ∧ t₁ = t₂
+  | [], [], t₁, t₂, h, _ => ⟨rfl, h⟩
+  | a :: s₁, b :: s₂, t₁, t₂, h, hl => by
+    simp [append_inj (cons.inj h).2 (Nat.succ.inj hl)] at h ⊢; exact h
+
+theorem append_inj_right (h : s₁ ++ t₁ = s₂ ++ t₂) (hl : length s₁ = length s₂) : t₁ = t₂ :=
+  (append_inj h hl).right
+
+theorem append_inj_left (h : s₁ ++ t₁ = s₂ ++ t₂) (hl : length s₁ = length s₂) : s₁ = s₂ :=
+  (append_inj h hl).left
+
+theorem append_inj' (h : s₁ ++ t₁ = s₂ ++ t₂) (hl : length t₁ = length t₂) : s₁ = s₂ ∧ t₁ = t₂ :=
+  append_inj h <| @Nat.add_right_cancel _ (length t₁) _ <| by
+  let hap := congrArg length h; simp only [length_append, ← hl] at hap; exact hap
+
+theorem append_inj_right' (h : s₁ ++ t₁ = s₂ ++ t₂) (hl : length t₁ = length t₂) : t₁ = t₂ :=
+  (append_inj' h hl).right
+
+theorem append_inj_left' (h : s₁ ++ t₁ = s₂ ++ t₂) (hl : length t₁ = length t₂) : s₁ = s₂ :=
+  (append_inj' h hl).left
+
+theorem append_right_inj {t₁ t₂ : List α} (s) : s ++ t₁ = s ++ t₂ ↔ t₁ = t₂ :=
+  ⟨fun h => append_inj_right h rfl, congrArg _⟩
+
+theorem append_left_inj {s₁ s₂ : List α} (t) : s₁ ++ t = s₂ ++ t ↔ s₁ = s₂ :=
+  ⟨fun h => append_inj_left' h rfl, congrArg (· ++ _)⟩
+
+@[simp] theorem append_eq_nil : p ++ q = [] ↔ p = [] ∧ q = [] := by
+  cases p <;> simp
+
+theorem get_append : ∀ {l₁ l₂ : List α} (n : Nat) (h : n < l₁.length),
+    (l₁ ++ l₂).get ⟨n, length_append .. ▸ Nat.lt_add_right _ h⟩ = l₁.get ⟨n, h⟩
+| a :: l, _, 0, h => rfl
+| a :: l, _, n+1, h => by simp only [get, cons_append]; apply get_append
+
+/-! ### map -/
+
+@[simp] theorem map_nil {f : α → β} : map f [] = [] := rfl
+
+@[simp] theorem map_cons (f : α → β) a l : map f (a :: l) = f a :: map f l := rfl
+
+@[simp] theorem map_append (f : α → β) : ∀ l₁ l₂, map f (l₁ ++ l₂) = map f l₁ ++ map f l₂ := by
+  intro l₁; induction l₁ <;> intros <;> simp_all
+
+@[simp] theorem map_id (l : List α) : map id l = l := by induction l <;> simp_all
+
+@[simp] theorem map_id' (l : List α) : map (fun a => a) l = l := by induction l <;> simp_all
+
+@[simp] theorem mem_map {f : α → β} : ∀ {l : List α}, b ∈ l.map f ↔ ∃ a, a ∈ l ∧ f a = b
+  | [] => by simp
+  | _ :: l => by simp [mem_map (l := l), eq_comm (a := b)]
+
+theorem mem_map_of_mem (f : α → β) (h : a ∈ l) : f a ∈ map f l := mem_map.2 ⟨_, h, rfl⟩
+
+@[simp] theorem map_map (g : β → γ) (f : α → β) (l : List α) :
+  map g (map f l) = map (g ∘ f) l := by induction l <;> simp_all
+
+/-! ### bind -/
+
+@[simp] theorem nil_bind (f : α → List β) : List.bind [] f = [] := by simp [join, List.bind]
+
+@[simp] theorem cons_bind x xs (f : α → List β) :
+  List.bind (x :: xs) f = f x ++ List.bind xs f := by simp [join, List.bind]
+
+@[simp] theorem append_bind xs ys (f : α → List β) :
+  List.bind (xs ++ ys) f = List.bind xs f ++ List.bind ys f := by
+  induction xs; {rfl}; simp_all [cons_bind, append_assoc]
+
+@[simp] theorem bind_id (l : List (List α)) : List.bind l id = l.join := by simp [List.bind]
+
+/-! ### join -/
+
+@[simp] theorem join_nil : List.join ([] : List (List α)) = [] := rfl
+
+@[simp] theorem join_cons : (l :: ls).join = l ++ ls.join := rfl
+
+/-! ### bounded quantifiers over Lists -/
+
+theorem forall_mem_cons {p : α → Prop} {a : α} {l : List α} :
+    (∀ x, x ∈ a :: l → p x) ↔ p a ∧ ∀ x, x ∈ l → p x :=
+  ⟨fun H => ⟨H _ (.head ..), fun _ h => H _ (.tail _ h)⟩,
+   fun ⟨H₁, H₂⟩ _ => fun | .head .. => H₁ | .tail _ h => H₂ _ h⟩
+
+/-! ### reverse -/
+
+@[simp] theorem reverseAux_nil : reverseAux [] r = r := rfl
+@[simp] theorem reverseAux_cons : reverseAux (a::l) r = reverseAux l (a::r) := rfl
+
+theorem reverseAux_eq (as bs : List α) : reverseAux as bs = reverse as ++ bs :=
+  reverseAux_eq_append ..
+
+theorem reverse_map (f : α → β) (l : List α) : (l.map f).reverse = l.reverse.map f := by
+  induction l <;> simp [*]
+
+@[simp] theorem reverse_eq_nil_iff {xs : List α} : xs.reverse = [] ↔ xs = [] := by
+  match xs with
+  | [] => simp
+  | x :: xs => simp
+
+/-! ### nth element -/
+
+theorem get_of_mem : ∀ {a} {l : List α}, a ∈ l → ∃ n, get l n = a
+  | _, _ :: _, .head .. => ⟨⟨0, Nat.succ_pos _⟩, rfl⟩
+  | _, _ :: _, .tail _ m => let ⟨⟨n, h⟩, e⟩ := get_of_mem m; ⟨⟨n+1, Nat.succ_lt_succ h⟩, e⟩
+
+theorem get_mem : ∀ (l : List α) n h, get l ⟨n, h⟩ ∈ l
+  | _ :: _, 0, _ => .head ..
+  | _ :: l, _+1, _ => .tail _ (get_mem l ..)
+
+theorem mem_iff_get {a} {l : List α} : a ∈ l ↔ ∃ n, get l n = a :=
+  ⟨get_of_mem, fun ⟨_, e⟩ => e ▸ get_mem ..⟩
+
+theorem get?_len_le : ∀ {l : List α} {n}, length l ≤ n → l.get? n = none
+  | [], _, _ => rfl
+  | _ :: l, _+1, h => get?_len_le (l := l) <| Nat.le_of_succ_le_succ h
+
+theorem get?_eq_get : ∀ {l : List α} {n} (h : n < l.length), l.get? n = some (get l ⟨n, h⟩)
+  | _ :: _, 0, _ => rfl
+  | _ :: l, _+1, _ => get?_eq_get (l := l) _
+
+theorem get?_eq_some : l.get? n = some a ↔ ∃ h, get l ⟨n, h⟩ = a :=
+  ⟨fun e =>
+    have : n < length l := Nat.gt_of_not_le fun hn => by cases get?_len_le hn ▸ e
+    ⟨this, by rwa [get?_eq_get this, Option.some.injEq] at e⟩,
+  fun ⟨h, e⟩ => e ▸ get?_eq_get _⟩
+
+@[simp] theorem get?_eq_none : l.get? n = none ↔ length l ≤ n :=
+  ⟨fun e => Nat.ge_of_not_lt (fun h' => by cases e ▸ get?_eq_some.2 ⟨h', rfl⟩), get?_len_le⟩
+
+@[simp] theorem get?_map (f : α → β) : ∀ l n, (map f l).get? n = (l.get? n).map f
+  | [], _ => rfl
+  | _ :: _, 0 => rfl
+  | _ :: l, n+1 => get?_map f l n
+
+theorem get?_append {l₁ l₂ : List α} {n : Nat} (hn : n < l₁.length) :
+  (l₁ ++ l₂).get? n = l₁.get? n := by
+  have hn' : n < (l₁ ++ l₂).length := Nat.lt_of_lt_of_le hn <|
+    length_append .. ▸ Nat.le_add_right ..
+  rw [get?_eq_get hn, get?_eq_get hn', get_append]
+
+@[simp] theorem get?_concat_length : ∀ (l : List α) (a : α), (l ++ [a]).get? l.length = some a
+  | [], a => rfl
+  | b :: l, a => by rw [cons_append, length_cons]; simp only [get?, get?_concat_length]
+
+theorem getLast_eq_get : ∀ (l : List α) (h : l ≠ []),
+    getLast l h = l.get ⟨l.length - 1, by
+      match l with
+      | [] => contradiction
+      | a :: l => exact Nat.le_refl _⟩
+  | [a], h => rfl
+  | a :: b :: l, h => by
+    simp [getLast, get, Nat.succ_sub_succ, getLast_eq_get]
+
+@[simp] theorem getLast?_nil : @getLast? α [] = none := rfl
+
+theorem getLast?_eq_getLast : ∀ l h, @getLast? α l = some (getLast l h)
+  | [], h => nomatch h rfl
+  | _::_, _ => rfl
+
+theorem getLast?_eq_get? : ∀ (l : List α), getLast? l = l.get? (l.length - 1)
+  | [] => rfl
+  | a::l => by rw [getLast?_eq_getLast (a::l) nofun, getLast_eq_get, get?_eq_get]
+
+@[simp] theorem getLast?_concat (l : List α) : getLast? (l ++ [a]) = some a := by
+  simp [getLast?_eq_get?, Nat.succ_sub_succ]
+
+theorem getD_eq_get? : ∀ l n (a : α), getD l n a = (get? l n).getD a
+  | [], _, _ => rfl
+  | _a::_, 0, _ => rfl
+  | _::l, _+1, _ => getD_eq_get? (l := l) ..
+
+theorem get?_append_right : ∀ {l₁ l₂ : List α} {n : Nat}, l₁.length ≤ n →
+  (l₁ ++ l₂).get? n = l₂.get? (n - l₁.length)
+| [], _, n, _ => rfl
+| a :: l, _, n+1, h₁ => by
+  rw [cons_append]
+  simp [Nat.succ_sub_succ_eq_sub, get?_append_right (Nat.lt_succ.1 h₁)]
+
+theorem get?_reverse' : ∀ {l : List α} (i j), i + j + 1 = length l →
+    get? l.reverse i = get? l j
+  | [], _, _, _ => rfl
+  | a::l, i, 0, h => by simp [Nat.succ.injEq] at h; simp [h, get?_append_right, Nat.succ.injEq]
+  | a::l, i, j+1, h => by
+    have := Nat.succ.inj h; simp at this ⊢
+    rw [get?_append, get?_reverse' _ j this]
+    rw [length_reverse, ← this]; apply Nat.lt_add_of_pos_right (Nat.succ_pos _)
+
+theorem get?_reverse {l : List α} (i) (h : i < length l) :
+    get? l.reverse i = get? l (l.length - 1 - i) :=
+  get?_reverse' _ _ <| by
+    rw [Nat.add_sub_of_le (Nat.le_sub_one_of_lt h),
+      Nat.sub_add_cancel (Nat.lt_of_le_of_lt (Nat.zero_le _) h)]
+
+@[simp] theorem getD_nil : getD [] n d = d := rfl
+
+@[simp] theorem getD_cons_zero : getD (x :: xs) 0 d = x := rfl
+
+@[simp] theorem getD_cons_succ : getD (x :: xs) (n + 1) d = getD xs n d := rfl
+
+/-! ### take and drop -/
+
+@[simp] theorem take_append_drop : ∀ (n : Nat) (l : List α), take n l ++ drop n l = l
+  | 0, _ => rfl
+  | _+1, [] => rfl
+  | n+1, x :: xs => congrArg (cons x) <| take_append_drop n xs
+
+@[simp] theorem length_drop : ∀ (i : Nat) (l : List α), length (drop i l) = length l - i
+  | 0, _ => rfl
+  | succ i, [] => Eq.symm (Nat.zero_sub (succ i))
+  | succ i, x :: l => calc
+    length (drop (succ i) (x :: l)) = length l - i := length_drop i l
+    _ = succ (length l) - succ i := (Nat.succ_sub_succ_eq_sub (length l) i).symm
+
+theorem drop_length_le {l : List α} (h : l.length ≤ i) : drop i l = [] :=
+  length_eq_zero.1 (length_drop .. ▸ Nat.sub_eq_zero_of_le h)
+
+theorem take_length_le {l : List α} (h : l.length ≤ i) : take i l = l := by
+  have := take_append_drop i l
+  rw [drop_length_le h, append_nil] at this; exact this
+
+@[simp] theorem take_zero (l : List α) : l.take 0 = [] := rfl
+
+@[simp] theorem take_nil : ([] : List α).take i = [] := by cases i <;> rfl
+
+@[simp] theorem take_cons_succ : (a::as).take (i+1) = a :: as.take i := rfl
+
+@[simp] theorem drop_zero (l : List α) : l.drop 0 = l := rfl
+
+@[simp] theorem drop_succ_cons : (a :: l).drop (n + 1) = l.drop n := rfl
+
+@[simp] theorem drop_length (l : List α) : drop l.length l = [] := drop_length_le (Nat.le_refl _)
+
+@[simp] theorem take_length (l : List α) : take l.length l = l := take_length_le (Nat.le_refl _)
+
+theorem take_concat_get (l : List α) (i : Nat) (h : i < l.length) :
+    (l.take i).concat l[i] = l.take (i+1) :=
+  Eq.symm <| (append_left_inj _).1 <| (take_append_drop (i+1) l).trans <| by
+    rw [concat_eq_append, append_assoc, singleton_append, get_drop_eq_drop, take_append_drop]
+
+theorem reverse_concat (l : List α) (a : α) : (l.concat a).reverse = a :: l.reverse := by
+  rw [concat_eq_append, reverse_append]; rfl
+
+/-! ### takeWhile and dropWhile -/
+
+@[simp] theorem dropWhile_nil : ([] : List α).dropWhile p = [] := rfl
+
+theorem dropWhile_cons :
+    (x :: xs : List α).dropWhile p = if p x then xs.dropWhile p else x :: xs := by
+  split <;> simp_all [dropWhile]
+
+/-! ### foldlM and foldrM -/
+
+@[simp] theorem foldlM_reverse [Monad m] (l : List α) (f : β → α → m β) (b) :
+    l.reverse.foldlM f b = l.foldrM (fun x y => f y x) b := rfl
+
+@[simp] theorem foldlM_nil [Monad m] (f : β → α → m β) (b) : [].foldlM f b = pure b := rfl
+
+@[simp] theorem foldlM_cons [Monad m] (f : β → α → m β) (b) (a) (l : List α) :
+    (a :: l).foldlM f b = f b a >>= l.foldlM f := by
+  simp [List.foldlM]
+
+@[simp] theorem foldlM_append [Monad m] [LawfulMonad m] (f : β → α → m β) (b) (l l' : List α) :
+    (l ++ l').foldlM f b = l.foldlM f b >>= l'.foldlM f := by
+  induction l generalizing b <;> simp [*]
+
+@[simp] theorem foldrM_nil [Monad m] (f : α → β → m β) (b) : [].foldrM f b = pure b := rfl
+
+@[simp] theorem foldrM_cons [Monad m] [LawfulMonad m] (a : α) (l) (f : α → β → m β) (b) :
+    (a :: l).foldrM f b = l.foldrM f b >>= f a := by
+  simp only [foldrM]
+  induction l <;> simp_all
+
+@[simp] theorem foldrM_reverse [Monad m] (l : List α) (f : α → β → m β) (b) :
+    l.reverse.foldrM f b = l.foldlM (fun x y => f y x) b :=
+  (foldlM_reverse ..).symm.trans <| by simp
+
+theorem foldl_eq_foldlM (f : β → α → β) (b) (l : List α) :
+    l.foldl f b = l.foldlM (m := Id) f b := by
+  induction l generalizing b <;> simp [*, foldl]
+
+theorem foldr_eq_foldrM (f : α → β → β) (b) (l : List α) :
+    l.foldr f b = l.foldrM (m := Id) f b := by
+  induction l <;> simp [*, foldr]
+
+/-! ### foldl and foldr -/
+
+@[simp] theorem foldl_reverse (l : List α) (f : β → α → β) (b) :
+    l.reverse.foldl f b = l.foldr (fun x y => f y x) b := by simp [foldl_eq_foldlM, foldr_eq_foldrM]
+
+@[simp] theorem foldr_reverse (l : List α) (f : α → β → β) (b) :
+    l.reverse.foldr f b = l.foldl (fun x y => f y x) b :=
+  (foldl_reverse ..).symm.trans <| by simp
+
+@[simp] theorem foldrM_append [Monad m] [LawfulMonad m] (f : α → β → m β) (b) (l l' : List α) :
+    (l ++ l').foldrM f b = l'.foldrM f b >>= l.foldrM f := by
+  induction l <;> simp [*]
+
+@[simp] theorem foldl_append {β : Type _} (f : β → α → β) (b) (l l' : List α) :
+    (l ++ l').foldl f b = l'.foldl f (l.foldl f b) := by simp [foldl_eq_foldlM]
+
+@[simp] theorem foldr_append (f : α → β → β) (b) (l l' : List α) :
+    (l ++ l').foldr f b = l.foldr f (l'.foldr f b) := by simp [foldr_eq_foldrM]
+
+@[simp] theorem foldl_nil : [].foldl f b = b := rfl
+
+@[simp] theorem foldl_cons (l : List α) (b : β) : (a :: l).foldl f b = l.foldl f (f b a) := rfl
+
+@[simp] theorem foldr_nil : [].foldr f b = b := rfl
+
+@[simp] theorem foldr_cons (l : List α) : (a :: l).foldr f b = f a (l.foldr f b) := rfl
+
+@[simp] theorem foldr_self_append (l : List α) : l.foldr cons l' = l ++ l' := by
+  induction l <;> simp [*]
+
+theorem foldr_self (l : List α) : l.foldr cons [] = l := by simp
+
+/-! ### mapM -/
+
+/-- Alternate (non-tail-recursive) form of mapM for proofs. -/
+def mapM' [Monad m] (f : α → m β) : List α → m (List β)
+  | [] => pure []
+  | a :: l => return (← f a) :: (← l.mapM' f)
+
+@[simp] theorem mapM'_nil [Monad m] {f : α → m β} : mapM' f [] = pure [] := rfl
+@[simp] theorem mapM'_cons [Monad m] {f : α → m β} :
+    mapM' f (a :: l) = return ((← f a) :: (← l.mapM' f)) :=
+  rfl
+
+theorem mapM'_eq_mapM [Monad m] [LawfulMonad m] (f : α → m β) (l : List α) :
+    mapM' f l = mapM f l := by simp [go, mapM] where
+  go : ∀ l acc, mapM.loop f l acc = return acc.reverse ++ (← mapM' f l)
+    | [], acc => by simp [mapM.loop, mapM']
+    | a::l, acc => by simp [go l, mapM.loop, mapM']
+
+@[simp] theorem mapM_nil [Monad m] (f : α → m β) : [].mapM f = pure [] := rfl
+
+@[simp] theorem mapM_cons [Monad m] [LawfulMonad m] (f : α → m β) :
+    (a :: l).mapM f = (return (← f a) :: (← l.mapM f)) := by simp [← mapM'_eq_mapM, mapM']
+
+@[simp] theorem mapM_append [Monad m] [LawfulMonad m] (f : α → m β) {l₁ l₂ : List α} :
+    (l₁ ++ l₂).mapM f = (return (← l₁.mapM f) ++ (← l₂.mapM f)) := by induction l₁ <;> simp [*]
+
+/-! ### forM -/
+
+-- We use `List.forM` as the simp normal form, rather that `ForM.forM`.
+-- As such we need to replace `List.forM_nil` and `List.forM_cons` from Lean:
+
+@[simp] theorem forM_nil' [Monad m] : ([] : List α).forM f = (pure .unit : m PUnit) := rfl
+
+@[simp] theorem forM_cons' [Monad m] :
+    (a::as).forM f = (f a >>= fun _ => as.forM f : m PUnit) :=
+  List.forM_cons _ _ _
+
+/-! ### eraseIdx -/
+
+@[simp] theorem eraseIdx_nil : ([] : List α).eraseIdx i = [] := rfl
+@[simp] theorem eraseIdx_cons_zero : (a::as).eraseIdx 0 = as := rfl
+@[simp] theorem eraseIdx_cons_succ : (a::as).eraseIdx (i+1) = a :: as.eraseIdx i := rfl
+
+/-! ### find? -/
+
+@[simp] theorem find?_nil : ([] : List α).find? p = none := rfl
+theorem find?_cons : (a::as).find? p = match p a with | true => some a | false => as.find? p :=
+  rfl
+
+/-! ### filter -/
+
+@[simp] theorem filter_nil (p : α → Bool) : filter p [] = [] := rfl
+
+@[simp] theorem filter_cons_of_pos {p : α → Bool} {a : α} (l) (pa : p a) :
+    filter p (a :: l) = a :: filter p l := by rw [filter, pa]
+
+@[simp] theorem filter_cons_of_neg {p : α → Bool} {a : α} (l) (pa : ¬ p a) :
+    filter p (a :: l) = filter p l := by rw [filter, eq_false_of_ne_true pa]
+
+theorem filter_cons :
+    (x :: xs : List α).filter p = if p x then x :: (xs.filter p) else xs.filter p := by
+  split <;> simp [*]
+
+theorem mem_filter : x ∈ filter p as ↔ x ∈ as ∧ p x := by
+  induction as with
+  | nil => simp [filter]
+  | cons a as ih =>
+    by_cases h : p a
+    · simp_all [or_and_left]
+    · simp_all [or_and_right]
+
+theorem filter_eq_nil {l} : filter p l = [] ↔ ∀ a, a ∈ l → ¬p a := by
+  simp only [eq_nil_iff_forall_not_mem, mem_filter, not_and]
+
+/-! ### findSome? -/
+
+@[simp] theorem findSome?_nil : ([] : List α).findSome? f = none := rfl
+theorem findSome?_cons {f : α → Option β} :
+    (a::as).findSome? f = match f a with | some b => some b | none => as.findSome? f :=
+  rfl
+
+/-! ### replace -/
+
+@[simp] theorem replace_nil [BEq α] : ([] : List α).replace a b = [] := rfl
+theorem replace_cons [BEq α] {a : α} :
+    (a::as).replace b c = match a == b with | true => c::as | false => a :: replace as b c :=
+  rfl
+@[simp] theorem replace_cons_self [BEq α] [LawfulBEq α] {a : α} : (a::as).replace a b = b::as := by
+  simp [replace_cons]
+
+/-! ### elem -/
+
+@[simp] theorem elem_nil [BEq α] : ([] : List α).elem a = false := rfl
+theorem elem_cons [BEq α] {a : α} :
+    (a::as).elem b = match b == a with | true => true | false => as.elem b :=
+  rfl
+@[simp] theorem elem_cons_self [BEq α] [LawfulBEq α] {a : α} : (a::as).elem a = true := by
+  simp [elem_cons]
+
+/-! ### lookup -/
+
+@[simp] theorem lookup_nil [BEq α] : ([] : List (α × β)).lookup a = none := rfl
+theorem lookup_cons [BEq α] {k : α} :
+    ((k,b)::es).lookup a = match a == k with | true => some b | false => es.lookup a :=
+  rfl
+@[simp] theorem lookup_cons_self [BEq α] [LawfulBEq α] {k : α} : ((k,b)::es).lookup k = some b := by
+  simp [lookup_cons]
+
+/-! ### zipWith -/
+
+@[simp] theorem zipWith_nil_left {f : α → β → γ} : zipWith f [] l = [] := by
+  rfl
+
+@[simp] theorem zipWith_nil_right {f : α → β → γ} : zipWith f l [] = [] := by
+  simp [zipWith]
+
+@[simp] theorem zipWith_cons_cons {f : α → β → γ} :
+    zipWith f (a :: as) (b :: bs) = f a b :: zipWith f as bs := by
+  rfl
+
+theorem zipWith_get? {f : α → β → γ} :
+    (List.zipWith f as bs).get? i = match as.get? i, bs.get? i with
+      | some a, some b => some (f a b) | _, _ => none := by
+  induction as generalizing bs i with
+  | nil => cases bs with
+    | nil => simp
+    | cons b bs => simp
+  | cons a as aih => cases bs with
+    | nil => simp
+    | cons b bs => cases i <;> simp_all
+
+/-! ### zipWithAll -/
+
+theorem zipWithAll_get? {f : Option α → Option β → γ} :
+    (zipWithAll f as bs).get? i = match as.get? i, bs.get? i with
+      | none, none => .none | a?, b? => some (f a? b?) := by
+  induction as generalizing bs i with
+  | nil => induction bs generalizing i with
+    | nil => simp
+    | cons b bs bih => cases i <;> simp_all
+  | cons a as aih => cases bs with
+    | nil =>
+      specialize @aih []
+      cases i <;> simp_all
+    | cons b bs => cases i <;> simp_all
+
+/-! ### zip -/
+
+@[simp] theorem zip_nil_left : zip ([] : List α) (l : List β)  = [] := by
+  rfl
+
+@[simp] theorem zip_nil_right : zip (l : List α) ([] : List β)  = [] := by
+  simp [zip]
+
+@[simp] theorem zip_cons_cons : zip (a :: as) (b :: bs) = (a, b) :: zip as bs := by
+  rfl
+
+/-! ### unzip -/
+
+@[simp] theorem unzip_nil : ([] : List (α × β)).unzip = ([], []) := rfl
+@[simp] theorem unzip_cons {h : α × β} :
+    (h :: t).unzip = match unzip t with | (al, bl) => (h.1::al, h.2::bl) := rfl
+
+/-! ### all / any -/
+
+@[simp] theorem all_eq_true {l : List α} : l.all p ↔ ∀ x, x ∈ l →  p x := by induction l <;> simp [*]
+
+@[simp] theorem any_eq_true {l : List α} : l.any p ↔ ∃ x, x ∈ l ∧ p x := by induction l <;> simp [*]
+
+/-! ### enumFrom -/
+
+@[simp] theorem enumFrom_nil : ([] : List α).enumFrom i = [] := rfl
+@[simp] theorem enumFrom_cons : (a::as).enumFrom i = (i, a) :: as.enumFrom (i+1) := rfl
+
+/-! ### iota -/
+
+@[simp] theorem iota_zero : iota 0 = [] := rfl
+@[simp] theorem iota_succ : iota (i+1) = (i+1) :: iota i := rfl
+
+/-! ### intersperse -/
+
+@[simp] theorem intersperse_nil (sep : α) : ([] : List α).intersperse sep = [] := rfl
+@[simp] theorem intersperse_single (sep : α) : [x].intersperse sep = [x] := rfl
+@[simp] theorem intersperse_cons₂ (sep : α) :
+    (x::y::zs).intersperse sep = x::sep::((y::zs).intersperse sep) := rfl
+
+/-! ### isPrefixOf -/
+
+@[simp] theorem isPrefixOf_nil_left [BEq α] : isPrefixOf ([] : List α) l = true := by
+  simp [isPrefixOf]
+@[simp] theorem isPrefixOf_cons_nil [BEq α] : isPrefixOf (a::as) ([] : List α) = false := rfl
+theorem isPrefixOf_cons₂ [BEq α] {a : α} :
+    isPrefixOf (a::as) (b::bs) = (a == b && isPrefixOf as bs) := rfl
+@[simp] theorem isPrefixOf_cons₂_self [BEq α] [LawfulBEq α] {a : α} :
+    isPrefixOf (a::as) (a::bs) = isPrefixOf as bs := by simp [isPrefixOf_cons₂]
+
+/-! ### isEqv -/
+
+@[simp] theorem isEqv_nil_nil : isEqv ([] : List α) [] eqv = true := rfl
+@[simp] theorem isEqv_nil_cons : isEqv ([] : List α) (a::as) eqv = false := rfl
+@[simp] theorem isEqv_cons_nil : isEqv (a::as : List α) [] eqv = false := rfl
+theorem isEqv_cons₂ : isEqv (a::as) (b::bs) eqv = (eqv a b && isEqv as bs eqv) := rfl
+
+/-! ### dropLast -/
+
+@[simp] theorem dropLast_nil : ([] : List α).dropLast = [] := rfl
+@[simp] theorem dropLast_single : [x].dropLast = [] := rfl
+@[simp] theorem dropLast_cons₂ :
+    (x::y::zs).dropLast = x :: (y::zs).dropLast := rfl
+
+-- We may want to replace these `simp` attributes with explicit equational lemmas,
+-- as we already have for all the non-monadic functions.
+attribute [simp] mapA forA filterAuxM firstM anyM allM findM? findSomeM?
+
+-- Previously `range.loop`, `mapM.loop`, `filterMapM.loop`, `forIn.loop`, `forIn'.loop`
+-- had attribute `@[simp]`.
+-- We don't currently provide simp lemmas,
+-- as this is an internal implementation and they don't seem to be needed.
+
+/-! ### minimum? -/
+
+@[simp] theorem minimum?_nil [Min α] : ([] : List α).minimum? = none := rfl
+
+-- We don't put `@[simp]` on `minimum?_cons`,
+-- because the definition in terms of `foldl` is not useful for proofs.
+theorem minimum?_cons [Min α] {xs : List α} : (x :: xs).minimum? = foldl min x xs := rfl
+
+@[simp] theorem minimum?_eq_none_iff {xs : List α} [Min α] : xs.minimum? = none ↔ xs = [] := by
+  cases xs <;> simp [minimum?]
+
+theorem minimum?_mem [Min α] (min_eq_or : ∀ a b : α, min a b = a ∨ min a b = b) :
+    {xs : List α} → xs.minimum? = some a → a ∈ xs := by
+  intro xs
+  match xs with
+  | nil => simp
+  | x :: xs =>
+    simp only [minimum?_cons, Option.some.injEq, List.mem_cons]
+    intro eq
+    induction xs generalizing x with
+    | nil =>
+      simp at eq
+      simp [eq]
+    | cons y xs ind =>
+      simp at eq
+      have p := ind _ eq
+      cases p with
+      | inl p =>
+        cases min_eq_or x y with | _ q => simp [p, q]
+      | inr p => simp [p, mem_cons]
+
+theorem le_minimum?_iff [Min α] [LE α]
+    (le_min_iff : ∀ a b c : α, a ≤ min b c ↔ a ≤ b ∧ a ≤ c) :
+    {xs : List α} → xs.minimum? = some a → ∀ x, x ≤ a ↔ ∀ b, b ∈ xs → x ≤ b
+  | nil => by simp
+  | cons x xs => by
+    rw [minimum?]
+    intro eq y
+    simp only [Option.some.injEq] at eq
+    induction xs generalizing x with
+    | nil =>
+      simp at eq
+      simp [eq]
+    | cons z xs ih =>
+      simp at eq
+      simp [ih _ eq, le_min_iff, and_assoc]
+
+-- This could be refactored by designing appropriate typeclasses to replace `le_refl`, `min_eq_or`,
+-- and `le_min_iff`.
+theorem minimum?_eq_some_iff [Min α] [LE α] [anti : Antisymm ((· : α) ≤ ·)]
+    (le_refl : ∀ a : α, a ≤ a)
+    (min_eq_or : ∀ a b : α, min a b = a ∨ min a b = b)
+    (le_min_iff : ∀ a b c : α, a ≤ min b c ↔ a ≤ b ∧ a ≤ c) {xs : List α} :
+    xs.minimum? = some a ↔ a ∈ xs ∧ ∀ b, b ∈ xs → a ≤ b := by
+  refine ⟨fun h => ⟨minimum?_mem min_eq_or h, (le_minimum?_iff le_min_iff h _).1 (le_refl _)⟩, ?_⟩
+  intro ⟨h₁, h₂⟩
+  cases xs with
+  | nil => simp at h₁
+  | cons x xs =>
+    exact congrArg some <| anti.1
+      ((le_minimum?_iff le_min_iff (xs := x::xs) rfl _).1 (le_refl _) _ h₁)
+      (h₂ _ (minimum?_mem min_eq_or (xs := x::xs) rfl))
+
+@[simp] theorem get_cons_succ {as : List α} {h : i + 1 < (a :: as).length} :
+  (a :: as).get ⟨i+1, h⟩ = as.get ⟨i, Nat.lt_of_succ_lt_succ h⟩ := rfl
+
+@[simp] theorem get_cons_succ' {as : List α} {i : Fin as.length} :
+  (a :: as).get i.succ = as.get i := rfl
+
+@[simp] theorem set_nil (n : Nat) (a : α) : [].set n a = [] := rfl
+
+@[simp] theorem set_zero (x : α) (xs : List α) (a : α) :
+  (x :: xs).set 0 a = a :: xs := rfl
+
+@[simp] theorem set_succ (x : α) (xs : List α) (n : Nat) (a : α) :
+  (x :: xs).set n.succ a = x :: xs.set n a := rfl
+
+@[simp] theorem get_set_eq (l : List α) (i : Nat) (a : α) (h : i < (l.set i a).length) :
+    (l.set i a).get ⟨i, h⟩ = a :=
+  match l, i with
+  | [], _ => by
+    simp at h
+    contradiction
+  | _ :: _, 0 => by
+    simp
+  | _ :: l, i + 1 => by
+    simp [get_set_eq l]
+
+@[simp] theorem get_set_ne (l : List α) {i j : Nat} (h : i ≠ j) (a : α)
+    (hj : j < (l.set i a).length) :
+    (l.set i a).get ⟨j, hj⟩ = l.get ⟨j, by simp at hj; exact hj⟩ :=
+  match l, i, j with
+  | [], _, _ => by
+    simp
+  | _ :: _, 0, 0 => by
+    contradiction
+  | _ :: _, 0, _ + 1 => by
+    simp
+  | _ :: _, _ + 1, 0 => by
+    simp
+  | _ :: l, i + 1, j + 1 => by
+    have g : i ≠ j := h ∘ congrArg (· + 1)
+    simp [get_set_ne l g]
+
+end List

src/Init/Data/Nat.lean

@@ -6,10 +6,17 @@ Authors: Leonardo de Moura
 prelude
 import Init.Data.Nat.Basic
 import Init.Data.Nat.Div
+import Init.Data.Nat.Dvd
 import Init.Data.Nat.Gcd
+import Init.Data.Nat.MinMax
 import Init.Data.Nat.Bitwise
 import Init.Data.Nat.Control
 import Init.Data.Nat.Log2
 import Init.Data.Nat.Power2
 import Init.Data.Nat.Linear
 import Init.Data.Nat.SOM
+import Init.Data.Nat.Lemmas
+import Init.Data.Nat.Mod
+import Init.Data.Nat.Lcm
+import Init.Data.Nat.Compare
+import Init.Data.Nat.Simproc

src/Init/Data/Nat/Basic.lean

@@ -10,6 +10,29 @@ universe u
 
 namespace Nat
 
+/-- Compiled version of `Nat.rec` so that we can define `Nat.recAux` to be defeq to `Nat.rec`.
+This is working around the fact that the compiler does not currently support recursors. -/
+private def recCompiled {motive : Nat → Sort u} (zero : motive zero) (succ : (n : Nat) → motive n → motive (Nat.succ n)) : (t : Nat) → motive t
+  | .zero => zero
+  | .succ n => succ n (recCompiled zero succ n)
+
+@[csimp]
+private theorem rec_eq_recCompiled : @Nat.rec = @Nat.recCompiled :=
+  funext fun _ => funext fun _ => funext fun succ => funext fun t =>
+    Nat.recOn t rfl (fun n ih => congrArg (succ n) ih)
+
+/-- Recursor identical to `Nat.rec` but uses notations `0` for `Nat.zero` and `· + 1` for `Nat.succ`.
+Used as the default `Nat` eliminator by the `induction` tactic. -/
+@[elab_as_elim, induction_eliminator]
+protected abbrev recAux {motive : Nat → Sort u} (zero : motive 0) (succ : (n : Nat) → motive n → motive (n + 1)) (t : Nat) : motive t :=
+  Nat.rec zero succ t
+
+/-- Recursor identical to `Nat.casesOn` but uses notations `0` for `Nat.zero` and `· + 1` for `Nat.succ`.
+Used as the default `Nat` eliminator by the `cases` tactic. -/
+@[elab_as_elim, cases_eliminator]
+protected abbrev casesAuxOn {motive : Nat → Sort u} (t : Nat) (zero : motive 0) (succ : (n : Nat) → motive (n + 1)) : motive t :=
+  Nat.casesOn t zero succ
+
 /--
 `Nat.fold` evaluates `f` on the numbers up to `n` exclusive, in increasing order:
 * `Nat.fold f 3 init = init |> f 0 |> f 1 |> f 2`
@@ -125,9 +148,12 @@ theorem add_succ (n m : Nat) : n + succ m = succ (n + m) :=
 theorem add_one (n : Nat) : n + 1 = succ n :=
   rfl
 
-theorem succ_eq_add_one (n : Nat) : succ n = n + 1 :=
+@[simp] theorem succ_eq_add_one (n : Nat) : succ n = n + 1 :=
   rfl
 
+@[simp] theorem add_one_ne_zero (n : Nat) : n + 1 ≠ 0 := nofun
+@[simp] theorem zero_ne_add_one (n : Nat) : 0 ≠ n + 1 := nofun
+
 protected theorem add_comm : ∀ (n m : Nat), n + m = m + n
   | n, 0   => Eq.symm (Nat.zero_add n)
   | n, m+1 => by
@@ -147,13 +173,20 @@ protected theorem add_right_comm (n m k : Nat) : (n + m) + k = (n + k) + m := by
 
 protected theorem add_left_cancel {n m k : Nat} : n + m = n + k → m = k := by
   induction n with
-  | zero => simp; intros; assumption
-  | succ n ih => simp [succ_add]; intro h; apply ih h
+  | zero => simp
+  | succ n ih => simp [succ_add, succ.injEq]; intro h; apply ih h
 
 protected theorem add_right_cancel {n m k : Nat} (h : n + m = k + m) : n = k := by
   rw [Nat.add_comm n m, Nat.add_comm k m] at h
   apply Nat.add_left_cancel h
 
+theorem eq_zero_of_add_eq_zero : ∀ {n m}, n + m = 0 → n = 0 ∧ m = 0
+  | 0, 0, _ => ⟨rfl, rfl⟩
+  | _+1, 0, h => Nat.noConfusion h
+
+protected theorem eq_zero_of_add_eq_zero_left (h : n + m = 0) : m = 0 :=
+  (Nat.eq_zero_of_add_eq_zero h).2
+
 /-! # Nat.mul theorems -/
 
 @[simp] protected theorem mul_zero (n : Nat) : n * 0 = 0 :=
@@ -182,7 +215,7 @@ protected theorem mul_comm : ∀ (n m : Nat), n * m = m * n
   Nat.mul_comm n 1 ▸ Nat.mul_one n
 
 protected theorem left_distrib (n m k : Nat) : n * (m + k) = n * m + n * k := by
-  induction n generalizing m k with
+  induction n with
   | zero      => repeat rw [Nat.zero_mul]
   | succ n ih => simp [succ_mul, ih]; rw [Nat.add_assoc, Nat.add_assoc (n*m)]; apply congrArg; apply Nat.add_left_comm
 
@@ -202,25 +235,25 @@ protected theorem mul_assoc : ∀ (n m k : Nat), (n * m) * k = n * (m * k)
 protected theorem mul_left_comm (n m k : Nat) : n * (m * k) = m * (n * k) := by
   rw [← Nat.mul_assoc, Nat.mul_comm n m, Nat.mul_assoc]
 
+protected theorem mul_two (n) : n * 2 = n + n := by rw [Nat.mul_succ, Nat.mul_one]
+protected theorem two_mul (n) : 2 * n = n + n := by rw [Nat.succ_mul, Nat.one_mul]
+
 /-! # Inequalities -/
 
 attribute [simp] Nat.le_refl
 
-theorem succ_lt_succ {n m : Nat} : n < m → succ n < succ m :=
-  succ_le_succ
+theorem succ_lt_succ {n m : Nat} : n < m → succ n < succ m := succ_le_succ
 
-theorem lt_succ_of_le {n m : Nat} : n ≤ m → n < succ m :=
-  succ_le_succ
+theorem lt_succ_of_le {n m : Nat} : n ≤ m → n < succ m := succ_le_succ
 
-@[simp] protected theorem sub_zero (n : Nat) : n - 0 = n :=
-  rfl
+@[simp] protected theorem sub_zero (n : Nat) : n - 0 = n := rfl
 
 theorem succ_sub_succ_eq_sub (n m : Nat) : succ n - succ m = n - m := by
   induction m with
   | zero      => exact rfl
   | succ m ih => apply congrArg pred ih
 
-theorem pred_le : ∀ (n : Nat), pred n ≤ n
+@[simp] theorem pred_le : ∀ (n : Nat), pred n ≤ n
   | zero   => Nat.le.refl
   | succ _ => le_succ _
 
@@ -241,8 +274,7 @@ theorem sub_lt : ∀ {n m : Nat}, 0 < n → 0 < m → n - m < n
       show n - m < succ n from
       lt_succ_of_le (sub_le n m)
 
-theorem sub_succ (n m : Nat) : n - succ m = pred (n - m) :=
-  rfl
+theorem sub_succ (n m : Nat) : n - succ m = pred (n - m) := rfl
 
 theorem succ_sub_succ (n m : Nat) : succ n - succ m = n - m :=
   succ_sub_succ_eq_sub n m
@@ -254,7 +286,7 @@ theorem succ_sub_succ (n m : Nat) : succ n - succ m = n - m :=
 theorem sub_add_eq (a b c : Nat) : a - (b + c) = a - b - c := by
   induction c with
   | zero => simp
-  | succ c ih => simp [Nat.add_succ, Nat.sub_succ, ih]
+  | succ c ih => simp only [Nat.add_succ, Nat.sub_succ, ih]
 
 protected theorem lt_of_lt_of_le {n m k : Nat} : n < m → m ≤ k → n < k :=
   Nat.le_trans
@@ -277,41 +309,33 @@ instance : Trans (. ≤ . : Nat → Nat → Prop) (. < . : Nat → Nat → Prop)
 protected theorem le_of_eq {n m : Nat} (p : n = m) : n ≤ m :=
   p ▸ Nat.le_refl n
 
-theorem le_of_succ_le {n m : Nat} (h : succ n ≤ m) : n ≤ m :=
-  Nat.le_trans (le_succ n) h
-
-protected theorem le_of_lt {n m : Nat} (h : n < m) : n ≤ m :=
-  le_of_succ_le h
-
 theorem lt.step {n m : Nat} : n < m → n < succ m := le_step
 
+theorem le_of_succ_le {n m : Nat} (h : succ n ≤ m) : n ≤ m := Nat.le_trans (le_succ n) h
+theorem lt_of_succ_lt      {n m : Nat} : succ n < m → n < m := le_of_succ_le
+protected theorem le_of_lt {n m : Nat} : n < m → n ≤ m := le_of_succ_le
+
+theorem lt_of_succ_lt_succ {n m : Nat} : succ n < succ m → n < m := le_of_succ_le_succ
+
+theorem lt_of_succ_le {n m : Nat} (h : succ n ≤ m) : n < m := h
+theorem succ_le_of_lt {n m : Nat} (h : n < m) : succ n ≤ m := h
+
 theorem eq_zero_or_pos : ∀ (n : Nat), n = 0 ∨ n > 0
   | 0   => Or.inl rfl
   | _+1 => Or.inr (succ_pos _)
 
+protected theorem pos_of_ne_zero {n : Nat} : n ≠ 0 → 0 < n := (eq_zero_or_pos n).resolve_left
+
 theorem lt.base (n : Nat) : n < succ n := Nat.le_refl (succ n)
 
-theorem lt_succ_self (n : Nat) : n < succ n := lt.base n
+@[simp] theorem lt_succ_self (n : Nat) : n < succ n := lt.base n
 
 protected theorem le_total (m n : Nat) : m ≤ n ∨ n ≤ m :=
   match Nat.lt_or_ge m n with
   | Or.inl h => Or.inl (Nat.le_of_lt h)
   | Or.inr h => Or.inr h
 
-theorem eq_zero_of_le_zero {n : Nat} (h : n ≤ 0) : n = 0 :=
-  Nat.le_antisymm h (zero_le _)
-
-theorem lt_of_succ_lt {n m : Nat} : succ n < m → n < m :=
-  le_of_succ_le
-
-theorem lt_of_succ_lt_succ {n m : Nat} : succ n < succ m → n < m :=
-  le_of_succ_le_succ
-
-theorem lt_of_succ_le {n m : Nat} (h : succ n ≤ m) : n < m :=
-  h
-
-theorem succ_le_of_lt {n m : Nat} (h : n < m) : succ n ≤ m :=
-  h
+theorem eq_zero_of_le_zero {n : Nat} (h : n ≤ 0) : n = 0 := Nat.le_antisymm h (zero_le _)
 
 theorem zero_lt_of_lt : {a b : Nat} → a < b → 0 < b
   | 0,   _, h => h
@@ -326,8 +350,7 @@ theorem zero_lt_of_ne_zero {a : Nat} (h : a ≠ 0) : 0 < a := by
 
 attribute [simp] Nat.lt_irrefl
 
-theorem ne_of_lt {a b : Nat} (h : a < b) : a ≠ b :=
-  fun he => absurd (he ▸ h) (Nat.lt_irrefl a)
+theorem ne_of_lt {a b : Nat} (h : a < b) : a ≠ b := fun he => absurd (he ▸ h) (Nat.lt_irrefl a)
 
 theorem le_or_eq_of_le_succ {m n : Nat} (h : m ≤ succ n) : m ≤ n ∨ m = succ n :=
   Decidable.byCases
@@ -344,6 +367,12 @@ theorem le_add_right : ∀ (n k : Nat), n ≤ n + k
 theorem le_add_left (n m : Nat): n ≤ m + n :=
   Nat.add_comm n m ▸ le_add_right n m
 
+protected theorem lt_add_left (c : Nat) (h : a < b) : a < c + b :=
+  Nat.lt_of_lt_of_le h (Nat.le_add_left ..)
+
+protected theorem lt_add_right (c : Nat) (h : a < b) : a < b + c :=
+  Nat.lt_of_lt_of_le h (Nat.le_add_right ..)
+
 theorem le.dest : ∀ {n m : Nat}, n ≤ m → Exists (fun k => n + k = m)
   | zero,   zero,   _ => ⟨0, rfl⟩
   | zero,   succ n, _ => ⟨succ n, Nat.add_comm 0 (succ n) ▸ rfl⟩
@@ -363,16 +392,51 @@ protected theorem not_le_of_gt {n m : Nat} (h : n > m) : ¬ n ≤ m := fun h₁
   | Or.inr h₂ =>
     have Heq : n = m := Nat.le_antisymm h₁ h₂
     absurd (@Eq.subst _ _ _ _ Heq h) (Nat.lt_irrefl m)
+protected theorem not_le_of_lt : ∀{a b : Nat}, a < b → ¬(b ≤ a) := Nat.not_le_of_gt
+protected theorem not_lt_of_ge : ∀{a b : Nat}, b ≥ a → ¬(b < a) := flip Nat.not_le_of_gt
+protected theorem not_lt_of_le : ∀{a b : Nat}, a ≤ b → ¬(b < a) := flip Nat.not_le_of_gt
+protected theorem lt_le_asymm : ∀{a b : Nat}, a < b → ¬(b ≤ a) := Nat.not_le_of_gt
+protected theorem le_lt_asymm : ∀{a b : Nat}, a ≤ b → ¬(b < a) := flip Nat.not_le_of_gt
 
-theorem gt_of_not_le {n m : Nat} (h : ¬ n ≤ m) : n > m :=
-  match Nat.lt_or_ge m n with
-  | Or.inl h₁ => h₁
-  | Or.inr h₁ => absurd h₁ h
+theorem gt_of_not_le {n m : Nat} (h : ¬ n ≤ m) : n > m := (Nat.lt_or_ge m n).resolve_right h
+protected theorem lt_of_not_ge : ∀{a b : Nat}, ¬(b ≥ a) → b < a := Nat.gt_of_not_le
+protected theorem lt_of_not_le : ∀{a b : Nat}, ¬(a ≤ b) → b < a := Nat.gt_of_not_le
 
-theorem ge_of_not_lt {n m : Nat} (h : ¬ n < m) : n ≥ m :=
-  match Nat.lt_or_ge n m with
-  | Or.inl h₁ => absurd h₁ h
-  | Or.inr h₁ => h₁
+theorem ge_of_not_lt {n m : Nat} (h : ¬ n < m) : n ≥ m := (Nat.lt_or_ge n m).resolve_left h
+protected theorem le_of_not_gt : ∀{a b : Nat}, ¬(b > a) → b ≤ a := Nat.ge_of_not_lt
+protected theorem le_of_not_lt : ∀{a b : Nat}, ¬(a < b) → b ≤ a := Nat.ge_of_not_lt
+
+theorem ne_of_gt {a b : Nat} (h : b < a) : a ≠ b := (ne_of_lt h).symm
+protected theorem ne_of_lt' : ∀{a b : Nat}, a < b → b ≠ a := ne_of_gt
+
+@[simp] protected theorem not_le {a b : Nat} : ¬ a ≤ b ↔ b < a :=
+  Iff.intro Nat.gt_of_not_le Nat.not_le_of_gt
+@[simp] protected theorem not_lt {a b : Nat} : ¬ a < b ↔ b ≤ a :=
+  Iff.intro Nat.ge_of_not_lt (flip Nat.not_le_of_gt)
+
+protected theorem le_of_not_le {a b : Nat} (h : ¬ b ≤ a) : a ≤ b := Nat.le_of_lt (Nat.not_le.1 h)
+protected theorem le_of_not_ge : ∀{a b : Nat}, ¬(a ≥ b) → a ≤ b:= @Nat.le_of_not_le
+
+protected theorem lt_trichotomy (a b : Nat) : a < b ∨ a = b ∨ b < a :=
+  match Nat.lt_or_ge a b with
+  | .inl h => .inl h
+  | .inr h =>
+    match Nat.eq_or_lt_of_le h with
+    | .inl h => .inr (.inl h.symm)
+    | .inr h => .inr (.inr h)
+
+protected theorem lt_or_gt_of_ne {a b : Nat} (ne : a ≠ b) : a < b ∨ a > b :=
+  match Nat.lt_trichotomy a b with
+  | .inl h => .inl h
+  | .inr (.inl e) => False.elim (ne e)
+  | .inr (.inr h) => .inr h
+
+protected theorem lt_or_lt_of_ne : ∀{a b : Nat}, a ≠ b → a < b ∨ b < a := Nat.lt_or_gt_of_ne
+
+protected theorem le_antisymm_iff {a b : Nat} : a = b ↔ a ≤ b ∧ b ≤ a :=
+  Iff.intro (fun p => And.intro (Nat.le_of_eq p) (Nat.le_of_eq p.symm))
+            (fun ⟨hle, hge⟩ => Nat.le_antisymm hle hge)
+protected theorem eq_iff_le_and_ge : ∀{a b : Nat}, a = b ↔ a ≤ b ∧ b ≤ a := @Nat.le_antisymm_iff
 
 instance : Antisymm ( . ≤ . : Nat → Nat → Prop) where
   antisymm h₁ h₂ := Nat.le_antisymm h₁ h₂
@@ -398,9 +462,14 @@ protected theorem add_lt_add_left {n m : Nat} (h : n < m) (k : Nat) : k + n < k
 protected theorem add_lt_add_right {n m : Nat} (h : n < m) (k : Nat) : n + k < m + k :=
   Nat.add_comm k m ▸ Nat.add_comm k n ▸ Nat.add_lt_add_left h k
 
+protected theorem lt_add_of_pos_right (h : 0 < k) : n < n + k :=
+  Nat.add_lt_add_left h n
+
 protected theorem zero_lt_one : 0 < (1:Nat) :=
   zero_lt_succ 0
 
+protected theorem pos_iff_ne_zero : 0 < n ↔ n ≠ 0 := ⟨ne_of_gt, Nat.pos_of_ne_zero⟩
+
 theorem add_le_add {a b c d : Nat} (h₁ : a ≤ b) (h₂ : c ≤ d) : a + c ≤ b + d :=
   Nat.le_trans (Nat.add_le_add_right h₁ c) (Nat.add_le_add_left h₂ b)
 
@@ -418,6 +487,140 @@ protected theorem le_of_add_le_add_right {a b c : Nat} : a + b ≤ c + b → a
   rw [Nat.add_comm _ b, Nat.add_comm _ b]
   apply Nat.le_of_add_le_add_left
 
+protected theorem add_le_add_iff_right {n : Nat} : m + n ≤ k + n ↔ m ≤ k :=
+  ⟨Nat.le_of_add_le_add_right, fun h => Nat.add_le_add_right h _⟩
+
+/-! ### le/lt -/
+
+protected theorem lt_asymm {a b : Nat} (h : a < b) : ¬ b < a := Nat.not_lt.2 (Nat.le_of_lt h)
+/-- Alias for `Nat.lt_asymm`. -/
+protected abbrev not_lt_of_gt := @Nat.lt_asymm
+/-- Alias for `Nat.lt_asymm`. -/
+protected abbrev not_lt_of_lt := @Nat.lt_asymm
+
+protected theorem lt_iff_le_not_le {m n : Nat} : m < n ↔ m ≤ n ∧ ¬ n ≤ m :=
+  ⟨fun h => ⟨Nat.le_of_lt h, Nat.not_le_of_gt h⟩, fun ⟨_, h⟩ => Nat.lt_of_not_ge h⟩
+/-- Alias for `Nat.lt_iff_le_not_le`. -/
+protected abbrev lt_iff_le_and_not_ge := @Nat.lt_iff_le_not_le
+
+protected theorem lt_iff_le_and_ne {m n : Nat} : m < n ↔ m ≤ n ∧ m ≠ n :=
+  ⟨fun h => ⟨Nat.le_of_lt h, Nat.ne_of_lt h⟩, fun h => Nat.lt_of_le_of_ne h.1 h.2⟩
+
+protected theorem ne_iff_lt_or_gt {a b : Nat} : a ≠ b ↔ a < b ∨ b < a :=
+  ⟨Nat.lt_or_gt_of_ne, fun | .inl h => Nat.ne_of_lt h | .inr h => Nat.ne_of_gt h⟩
+/-- Alias for `Nat.ne_iff_lt_or_gt`. -/
+protected abbrev lt_or_gt := @Nat.ne_iff_lt_or_gt
+
+/-- Alias for `Nat.le_total`. -/
+protected abbrev le_or_ge := @Nat.le_total
+/-- Alias for `Nat.le_total`. -/
+protected abbrev le_or_le := @Nat.le_total
+
+protected theorem eq_or_lt_of_not_lt {a b : Nat} (hnlt : ¬ a < b) : a = b ∨ b < a :=
+  (Nat.lt_trichotomy ..).resolve_left hnlt
+
+protected theorem lt_or_eq_of_le {n m : Nat} (h : n ≤ m) : n < m ∨ n = m :=
+  (Nat.lt_or_ge ..).imp_right (Nat.le_antisymm h)
+
+protected theorem le_iff_lt_or_eq {n m : Nat} : n ≤ m ↔ n < m ∨ n = m :=
+  ⟨Nat.lt_or_eq_of_le, fun | .inl h => Nat.le_of_lt h | .inr rfl => Nat.le_refl _⟩
+
+protected theorem lt_succ_iff : m < succ n ↔ m ≤ n := ⟨le_of_lt_succ, lt_succ_of_le⟩
+
+protected theorem lt_succ_iff_lt_or_eq : m < succ n ↔ m < n ∨ m = n :=
+  Nat.lt_succ_iff.trans Nat.le_iff_lt_or_eq
+
+protected theorem eq_of_lt_succ_of_not_lt (hmn : m < n + 1) (h : ¬ m < n) : m = n :=
+  (Nat.lt_succ_iff_lt_or_eq.1 hmn).resolve_left h
+
+protected theorem eq_of_le_of_lt_succ (h₁ : n ≤ m) (h₂ : m < n + 1) : m = n :=
+  Nat.le_antisymm (le_of_succ_le_succ h₂) h₁
+
+
+/-! ## zero/one/two -/
+
+theorem le_zero : i ≤ 0 ↔ i = 0 := ⟨Nat.eq_zero_of_le_zero, fun | rfl => Nat.le_refl _⟩
+
+/-- Alias for `Nat.zero_lt_one`. -/
+protected abbrev one_pos := @Nat.zero_lt_one
+
+protected theorem two_pos : 0 < 2 := Nat.zero_lt_succ _
+
+protected theorem ne_zero_iff_zero_lt : n ≠ 0 ↔ 0 < n := Nat.pos_iff_ne_zero.symm
+
+protected theorem zero_lt_two : 0 < 2 := Nat.zero_lt_succ _
+
+protected theorem one_lt_two : 1 < 2 := Nat.succ_lt_succ Nat.zero_lt_one
+
+protected theorem eq_zero_of_not_pos (h : ¬0 < n) : n = 0 :=
+  Nat.eq_zero_of_le_zero (Nat.not_lt.1 h)
+
+/-! ## succ/pred -/
+
+attribute [simp] zero_lt_succ
+
+theorem succ_ne_self (n) : succ n ≠ n := Nat.ne_of_gt (lt_succ_self n)
+
+theorem succ_le : succ n ≤ m ↔ n < m := .rfl
+
+theorem lt_succ : m < succ n ↔ m ≤ n := ⟨le_of_lt_succ, lt_succ_of_le⟩
+
+theorem lt_succ_of_lt (h : a < b) : a < succ b := le_succ_of_le h
+
+theorem succ_pred_eq_of_ne_zero : ∀ {n}, n ≠ 0 → succ (pred n) = n
+  | _+1, _ => rfl
+
+theorem eq_zero_or_eq_succ_pred : ∀ n, n = 0 ∨ n = succ (pred n)
+  | 0 => .inl rfl
+  | _+1 => .inr rfl
+
+theorem succ_inj' : succ a = succ b ↔ a = b := (Nat.succ.injEq a b).to_iff
+
+theorem succ_le_succ_iff : succ a ≤ succ b ↔ a ≤ b := ⟨le_of_succ_le_succ, succ_le_succ⟩
+
+theorem succ_lt_succ_iff : succ a < succ b ↔ a < b := ⟨lt_of_succ_lt_succ, succ_lt_succ⟩
+
+theorem pred_inj : ∀ {a b}, 0 < a → 0 < b → pred a = pred b → a = b
+  | _+1, _+1, _, _ => congrArg _
+
+theorem pred_ne_self : ∀ {a}, a ≠ 0 → pred a ≠ a
+  | _+1, _ => (succ_ne_self _).symm
+
+theorem pred_lt_self : ∀ {a}, 0 < a → pred a < a
+  | _+1, _ => lt_succ_self _
+
+theorem pred_lt_pred : ∀ {n m}, n ≠ 0 → n < m → pred n < pred m
+  | _+1, _+1, _, h => lt_of_succ_lt_succ h
+
+theorem pred_le_iff_le_succ : ∀ {n m}, pred n ≤ m ↔ n ≤ succ m
+  | 0, _ => ⟨fun _ => Nat.zero_le _, fun _ => Nat.zero_le _⟩
+  | _+1, _ => Nat.succ_le_succ_iff.symm
+
+theorem le_succ_of_pred_le : pred n ≤ m → n ≤ succ m := pred_le_iff_le_succ.1
+
+theorem pred_le_of_le_succ : n ≤ succ m → pred n ≤ m := pred_le_iff_le_succ.2
+
+theorem lt_pred_iff_succ_lt : ∀ {n m}, n < pred m ↔ succ n < m
+  | _, 0 => ⟨nofun, nofun⟩
+  | _, _+1 => Nat.succ_lt_succ_iff.symm
+
+theorem succ_lt_of_lt_pred : n < pred m → succ n < m := lt_pred_iff_succ_lt.1
+
+theorem lt_pred_of_succ_lt : succ n < m → n < pred m := lt_pred_iff_succ_lt.2
+
+theorem le_pred_iff_lt : ∀ {n m}, 0 < m → (n ≤ pred m ↔ n < m)
+  | 0, _+1, _ => ⟨fun _ => Nat.zero_lt_succ _, fun _ => Nat.zero_le _⟩
+  | _+1, _+1, _ => Nat.lt_pred_iff_succ_lt
+
+theorem le_pred_of_lt (h : n < m) : n ≤ pred m := (le_pred_iff_lt (Nat.zero_lt_of_lt h)).2 h
+
+theorem le_sub_one_of_lt : a < b → a ≤ b - 1 := Nat.le_pred_of_lt
+
+theorem lt_of_le_pred (h : 0 < m) : n ≤ pred m → n < m := (le_pred_iff_lt h).1
+
+theorem exists_eq_succ_of_ne_zero : ∀ {n}, n ≠ 0 → Exists fun k => n = succ k
+  | _+1, _ => ⟨_, rfl⟩
+
 /-! # Basic theorems for comparing numerals -/
 
 theorem ctor_eq_zero : Nat.zero = 0 :=
@@ -429,7 +632,7 @@ protected theorem one_ne_zero : 1 ≠ (0 : Nat) :=
 protected theorem zero_ne_one : 0 ≠ (1 : Nat) :=
   fun h => Nat.noConfusion h
 
-theorem succ_ne_zero (n : Nat) : succ n ≠ 0 :=
+@[simp] theorem succ_ne_zero (n : Nat) : succ n ≠ 0 :=
   fun h => Nat.noConfusion h
 
 /-! # mul + order -/
@@ -470,10 +673,10 @@ theorem eq_of_mul_eq_mul_right {n m k : Nat} (hm : 0 < m) (h : n * m = k * m) :
 
 /-! # power -/
 
-theorem pow_succ (n m : Nat) : n^(succ m) = n^m * n :=
+protected theorem pow_succ (n m : Nat) : n^(succ m) = n^m * n :=
   rfl
 
-theorem pow_zero (n : Nat) : n^0 = 1 := rfl
+protected theorem pow_zero (n : Nat) : n^0 = 1 := rfl
 
 theorem pow_le_pow_of_le_left {n m : Nat} (h : n ≤ m) : ∀ (i : Nat), n^i ≤ m^i
   | 0      => Nat.le_refl _
@@ -527,7 +730,25 @@ theorem not_eq_zero_of_lt (h : b < a) : a ≠ 0 := by
 theorem pred_lt' {n m : Nat} (h : m < n) : pred n < n :=
   pred_lt (not_eq_zero_of_lt h)
 
-/-! # sub/pred theorems -/
+/-! # pred theorems -/
+
+@[simp] protected theorem pred_zero : pred 0 = 0 := rfl
+@[simp] protected theorem pred_succ (n : Nat) : pred n.succ = n := rfl
+
+theorem succ_pred {a : Nat} (h : a ≠ 0) : a.pred.succ = a := by
+  induction a with
+  | zero => contradiction
+  | succ => rfl
+
+theorem succ_pred_eq_of_pos : ∀ {n}, 0 < n → succ (pred n) = n
+  | _+1, _ => rfl
+
+theorem sub_one_add_one_eq_of_pos : ∀ {n}, 0 < n → (n - 1) + 1 = n
+  | _+1, _ => rfl
+
+@[simp] theorem pred_eq_sub_one : pred n = n - 1 := rfl
+
+/-! # sub theorems -/
 
 theorem add_sub_self_left (a b : Nat) : (a + b) - a = b := by
   induction a with
@@ -549,7 +770,7 @@ theorem zero_lt_sub_of_lt (h : i < a) : 0 < a - i := by
   | zero => contradiction
   | succ a ih =>
     match Nat.eq_or_lt_of_le h with
-    | Or.inl h => injection h with h; subst h; rw [←Nat.add_one, Nat.add_sub_self_left]; decide
+    | Or.inl h => injection h with h; subst h; rw [Nat.add_sub_self_left]; decide
     | Or.inr h =>
       have : 0 < a - i := ih (Nat.lt_of_succ_lt_succ h)
       exact Nat.lt_of_lt_of_le this (Nat.sub_le_succ_sub _ _)
@@ -561,14 +782,9 @@ theorem sub_succ_lt_self (a i : Nat) (h : i < a) : a - (i + 1) < a - i := by
   apply Nat.zero_lt_sub_of_lt
   assumption
 
-theorem succ_pred {a : Nat} (h : a ≠ 0) : a.pred.succ = a := by
-  induction a with
-  | zero => contradiction
-  | succ => rfl
-
 theorem sub_ne_zero_of_lt : {a b : Nat} → a < b → b - a ≠ 0
   | 0, 0, h      => absurd h (Nat.lt_irrefl 0)
-  | 0, succ b, _ => by simp
+  | 0, succ b, _ => by simp only [Nat.sub_zero, ne_eq, not_false_eq_true]
   | succ a, 0, h => absurd h (Nat.not_lt_zero a.succ)
   | succ a, succ b, h => by rw [Nat.succ_sub_succ]; exact sub_ne_zero_of_lt (Nat.lt_of_succ_lt_succ h)
 
@@ -580,18 +796,18 @@ theorem add_sub_of_le {a b : Nat} (h : a ≤ b) : a + (b - a) = b := by
     have : a ≤ b := Nat.le_of_succ_le h
     rw [sub_succ, Nat.succ_add, ← Nat.add_succ, Nat.succ_pred hne, ih this]
 
-protected theorem sub_add_cancel {n m : Nat} (h : m ≤ n) : n - m + m = n := by
+@[simp] protected theorem sub_add_cancel {n m : Nat} (h : m ≤ n) : n - m + m = n := by
   rw [Nat.add_comm, Nat.add_sub_of_le h]
 
 protected theorem add_sub_add_right (n k m : Nat) : (n + k) - (m + k) = n - m := by
   induction k with
   | zero => simp
-  | succ k ih => simp [add_succ, add_succ, succ_sub_succ, ih]
+  | succ k ih => simp [← Nat.add_assoc, succ_sub_succ_eq_sub, ih]
 
 protected theorem add_sub_add_left (k n m : Nat) : (k + n) - (k + m) = n - m := by
   rw [Nat.add_comm k n, Nat.add_comm k m, Nat.add_sub_add_right]
 
-protected theorem add_sub_cancel (n m : Nat) : n + m - m = n :=
+@[simp] protected theorem add_sub_cancel (n m : Nat) : n + m - m = n :=
   suffices n + m - (0 + m) = n by rw [Nat.zero_add] at this; assumption
   by rw [Nat.add_sub_add_right, Nat.sub_zero]
 
@@ -680,12 +896,6 @@ theorem lt_sub_of_add_lt {a b c : Nat} (h : a + b < c) : a < c - b :=
   have : a.succ + b ≤ c := by simp [Nat.succ_add]; exact h
   le_sub_of_add_le this
 
-@[simp] protected theorem pred_zero : pred 0 = 0 :=
-  rfl
-
-@[simp] protected theorem pred_succ (n : Nat) : pred n.succ = n :=
-  rfl
-
 theorem sub.elim {motive : Nat → Prop}
     (x y : Nat)
     (h₁ : y ≤ x → (k : Nat) → x = y + k → motive k)
@@ -695,18 +905,75 @@ theorem sub.elim {motive : Nat → Prop}
   | inl hlt => rw [Nat.sub_eq_zero_of_le (Nat.le_of_lt hlt)]; exact h₂ hlt
   | inr hle => exact h₁ hle (x - y) (Nat.add_sub_of_le hle).symm
 
+theorem succ_sub {m n : Nat} (h : n ≤ m) : succ m - n = succ (m - n) := by
+  let ⟨k, hk⟩ := Nat.le.dest h
+  rw [← hk, Nat.add_sub_cancel_left, ← add_succ, Nat.add_sub_cancel_left]
+
+protected theorem sub_pos_of_lt (h : m < n) : 0 < n - m :=
+  Nat.pos_iff_ne_zero.2 (Nat.sub_ne_zero_of_lt h)
+
+protected theorem sub_sub (n m k : Nat) : n - m - k = n - (m + k) := by
+  induction k with
+  | zero => simp
+  | succ k ih => rw [Nat.add_succ, Nat.sub_succ, Nat.add_succ, Nat.sub_succ, ih]
+
+protected theorem sub_le_sub_left (h : n ≤ m) (k : Nat) : k - m ≤ k - n :=
+  match m, le.dest h with
+  | _, ⟨a, rfl⟩ => by rw [← Nat.sub_sub]; apply sub_le
+
+protected theorem sub_le_sub_right {n m : Nat} (h : n ≤ m) : ∀ k, n - k ≤ m - k
+  | 0   => h
+  | z+1 => pred_le_pred (Nat.sub_le_sub_right h z)
+
+protected theorem lt_of_sub_ne_zero (h : n - m ≠ 0) : m < n :=
+  Nat.not_le.1 (mt Nat.sub_eq_zero_of_le h)
+
+protected theorem sub_ne_zero_iff_lt : n - m ≠ 0 ↔ m < n :=
+  ⟨Nat.lt_of_sub_ne_zero, Nat.sub_ne_zero_of_lt⟩
+
+protected theorem lt_of_sub_pos (h : 0 < n - m) : m < n :=
+  Nat.lt_of_sub_ne_zero (Nat.pos_iff_ne_zero.1 h)
+
+protected theorem lt_of_sub_eq_succ (h : m - n = succ l) : n < m :=
+  Nat.lt_of_sub_pos (h ▸ Nat.zero_lt_succ _)
+
+protected theorem sub_lt_left_of_lt_add {n k m : Nat} (H : n ≤ k) (h : k < n + m) : k - n < m := by
+  have := Nat.sub_le_sub_right (succ_le_of_lt h) n
+  rwa [Nat.add_sub_cancel_left, Nat.succ_sub H] at this
+
+protected theorem sub_lt_right_of_lt_add {n k m : Nat} (H : n ≤ k) (h : k < m + n) : k - n < m :=
+  Nat.sub_lt_left_of_lt_add H (Nat.add_comm .. ▸ h)
+
+protected theorem le_of_sub_eq_zero : ∀ {n m}, n - m = 0 → n ≤ m
+  | 0, _, _ => Nat.zero_le ..
+  | _+1, _+1, h => Nat.succ_le_succ <| Nat.le_of_sub_eq_zero (Nat.succ_sub_succ .. ▸ h)
+
+protected theorem le_of_sub_le_sub_right : ∀ {n m k : Nat}, k ≤ m → n - k ≤ m - k → n ≤ m
+  | 0, _, _, _, _ => Nat.zero_le ..
+  | _+1, _, 0, _, h₁ => h₁
+  | _+1, _+1, _+1, h₀, h₁ => by
+    simp only [Nat.succ_sub_succ] at h₁
+    exact succ_le_succ <| Nat.le_of_sub_le_sub_right (le_of_succ_le_succ h₀) h₁
+
+protected theorem sub_le_sub_iff_right {n : Nat} (h : k ≤ m) : n - k ≤ m - k ↔ n ≤ m :=
+  ⟨Nat.le_of_sub_le_sub_right h, fun h => Nat.sub_le_sub_right h _⟩
+
+protected theorem sub_eq_iff_eq_add {c : Nat} (h : b ≤ a) : a - b = c ↔ a = c + b :=
+  ⟨fun | rfl => by rw [Nat.sub_add_cancel h], fun heq => by rw [heq, Nat.add_sub_cancel]⟩
+
+protected theorem sub_eq_iff_eq_add' {c : Nat} (h : b ≤ a) : a - b = c ↔ a = b + c := by
+  rw [Nat.add_comm, Nat.sub_eq_iff_eq_add h]
+
 theorem mul_pred_left (n m : Nat) : pred n * m = n * m - m := by
   cases n with
   | zero   => simp
   | succ n => rw [Nat.pred_succ, succ_mul, Nat.add_sub_cancel]
 
+/-! ## Mul sub distrib -/
+
 theorem mul_pred_right (n m : Nat) : n * pred m = n * m - n := by
   rw [Nat.mul_comm, mul_pred_left, Nat.mul_comm]
 
-protected theorem sub_sub (n m k : Nat) : n - m - k = n - (m + k) := by
-  induction k with
-  | zero => simp
-  | succ k ih => rw [Nat.add_succ, Nat.sub_succ, Nat.sub_succ, ih]
 
 protected theorem mul_sub_right_distrib (n m k : Nat) : (n - m) * k = n * k - m * k := by
   induction m with
@@ -719,14 +986,12 @@ protected theorem mul_sub_left_distrib (n m k : Nat) : n * (m - k) = n * m - n *
 /-! # Helper normalization theorems -/
 
 theorem not_le_eq (a b : Nat) : (¬ (a ≤ b)) = (b + 1 ≤ a) :=
-  propext <| Iff.intro (fun h => Nat.gt_of_not_le h) (fun h => Nat.not_le_of_gt h)
-
+  Eq.propIntro Nat.gt_of_not_le Nat.not_le_of_gt
 theorem not_ge_eq (a b : Nat) : (¬ (a ≥ b)) = (a + 1 ≤ b) :=
   not_le_eq b a
 
 theorem not_lt_eq (a b : Nat) : (¬ (a < b)) = (b ≤ a) :=
-  propext <| Iff.intro (fun h => have h := Nat.succ_le_of_lt (Nat.gt_of_not_le h); Nat.le_of_succ_le_succ h) (fun h => Nat.not_le_of_gt (Nat.succ_le_succ h))
-
+  Eq.propIntro Nat.le_of_not_lt Nat.not_lt_of_le
 theorem not_gt_eq (a b : Nat) : (¬ (a > b)) = (a ≤ b) :=
   not_lt_eq b a
 

src/Init/Data/Nat/Bitwise.lean

@@ -1,54 +1,8 @@
 /-
-Copyright (c) 2019 Microsoft Corporation. All rights reserved.
+Copyright (c) 2024 Lean FRO, LLC. All rights reserved.
 Released under Apache 2.0 license as described in the file LICENSE.
-Authors: Leonardo de Moura
+Authors: Scott Morrison
 -/
 prelude
-import Init.Data.Nat.Basic
-import Init.Data.Nat.Div
-import Init.Coe
-
-namespace Nat
-
-theorem bitwise_rec_lemma {n : Nat} (hNe : n ≠ 0) : n / 2 < n :=
-  Nat.div_lt_self (Nat.zero_lt_of_ne_zero hNe) (Nat.lt_succ_self _)
-
-def bitwise (f : Bool → Bool → Bool) (n m : Nat) : Nat :=
-  if n = 0 then
-    if f false true then m else 0
-  else if m = 0 then
-    if f true false then n else 0
-  else
-    let n' := n / 2
-    let m' := m / 2
-    let b₁ := n % 2 = 1
-    let b₂ := m % 2 = 1
-    let r  := bitwise f n' m'
-    if f b₁ b₂ then
-      r+r+1
-    else
-      r+r
-decreasing_by apply bitwise_rec_lemma; assumption
-
-@[extern "lean_nat_land"]
-def land : @& Nat → @& Nat → Nat := bitwise and
-@[extern "lean_nat_lor"]
-def lor  : @& Nat → @& Nat → Nat := bitwise or
-@[extern "lean_nat_lxor"]
-def xor  : @& Nat → @& Nat → Nat := bitwise bne
-@[extern "lean_nat_shiftl"]
-def shiftLeft : @& Nat → @& Nat → Nat
-  | n, 0 => n
-  | n, succ m => shiftLeft (2*n) m
-@[extern "lean_nat_shiftr"]
-def shiftRight : @& Nat → @& Nat → Nat
-  | n, 0 => n
-  | n, succ m => shiftRight n m / 2
-
-instance : AndOp Nat := ⟨Nat.land⟩
-instance : OrOp Nat := ⟨Nat.lor⟩
-instance : Xor Nat := ⟨Nat.xor⟩
-instance : ShiftLeft Nat := ⟨Nat.shiftLeft⟩
-instance : ShiftRight Nat := ⟨Nat.shiftRight⟩
-
-end Nat
+import Init.Data.Nat.Bitwise.Basic
+import Init.Data.Nat.Bitwise.Lemmas

src/Init/Data/Nat/Bitwise/Basic.lean

@@ -0,0 +1,83 @@
+/-
+Copyright (c) 2019 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Leonardo de Moura
+-/
+prelude
+import Init.Data.Nat.Basic
+import Init.Data.Nat.Div
+import Init.Coe
+
+namespace Nat
+
+theorem bitwise_rec_lemma {n : Nat} (hNe : n ≠ 0) : n / 2 < n :=
+  Nat.div_lt_self (Nat.zero_lt_of_ne_zero hNe) (Nat.lt_succ_self _)
+
+def bitwise (f : Bool → Bool → Bool) (n m : Nat) : Nat :=
+  if n = 0 then
+    if f false true then m else 0
+  else if m = 0 then
+    if f true false then n else 0
+  else
+    let n' := n / 2
+    let m' := m / 2
+    let b₁ := n % 2 = 1
+    let b₂ := m % 2 = 1
+    let r  := bitwise f n' m'
+    if f b₁ b₂ then
+      r+r+1
+    else
+      r+r
+decreasing_by apply bitwise_rec_lemma; assumption
+
+@[extern "lean_nat_land"]
+def land : @& Nat → @& Nat → Nat := bitwise and
+@[extern "lean_nat_lor"]
+def lor  : @& Nat → @& Nat → Nat := bitwise or
+@[extern "lean_nat_lxor"]
+def xor  : @& Nat → @& Nat → Nat := bitwise bne
+@[extern "lean_nat_shiftl"]
+def shiftLeft : @& Nat → @& Nat → Nat
+  | n, 0 => n
+  | n, succ m => shiftLeft (2*n) m
+@[extern "lean_nat_shiftr"]
+def shiftRight : @& Nat → @& Nat → Nat
+  | n, 0 => n
+  | n, succ m => shiftRight n m / 2
+
+instance : AndOp Nat := ⟨Nat.land⟩
+instance : OrOp Nat := ⟨Nat.lor⟩
+instance : Xor Nat := ⟨Nat.xor⟩
+instance : ShiftLeft Nat := ⟨Nat.shiftLeft⟩
+instance : ShiftRight Nat := ⟨Nat.shiftRight⟩
+
+theorem shiftLeft_eq (a b : Nat) : a <<< b = a * 2 ^ b :=
+  match b with
+  | 0 => (Nat.mul_one _).symm
+  | b+1 => (shiftLeft_eq _ b).trans <| by
+    simp [Nat.pow_succ, Nat.mul_assoc, Nat.mul_left_comm, Nat.mul_comm]
+
+@[simp] theorem shiftRight_zero : n >>> 0 = n := rfl
+
+theorem shiftRight_succ (m n) : m >>> (n + 1) = (m >>> n) / 2 := rfl
+
+theorem shiftRight_add (m n : Nat) : ∀ k, m >>> (n + k) = (m >>> n) >>> k
+  | 0 => rfl
+  | k + 1 => by simp [← Nat.add_assoc, shiftRight_add _ _ k, shiftRight_succ]
+
+theorem shiftRight_eq_div_pow (m : Nat) : ∀ n, m >>> n = m / 2 ^ n
+  | 0 => (Nat.div_one _).symm
+  | k + 1 => by
+    rw [shiftRight_add, shiftRight_eq_div_pow m k]
+    simp [Nat.div_div_eq_div_mul, ← Nat.pow_succ, shiftRight_succ]
+
+/-!
+### testBit
+We define an operation for testing individual bits in the binary representation
+of a number.
+-/
+
+/-- `testBit m n` returns whether the `(n+1)` least significant bit is `1` or `0`-/
+def testBit (m n : Nat) : Bool := (m >>> n) &&& 1 != 0
+
+end Nat

src/Init/Data/Nat/Bitwise/Lemmas.lean

@@ -0,0 +1,489 @@
+/-
+Copyright (c) 2024 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Joe Hendrix
+-/
+
+prelude
+import Init.Data.Bool
+import Init.Data.Int.Pow
+import Init.Data.Nat.Bitwise.Basic
+import Init.Data.Nat.Lemmas
+import Init.Data.Nat.Simproc
+import Init.TacticsExtra
+import Init.Omega
+
+/-
+This module defines properties of the bitwise operations on Natural numbers.
+
+It is primarily intended to support the bitvector library.
+-/
+
+namespace Nat
+
+@[local simp]
+private theorem one_div_two : 1/2 = 0 := by trivial
+
+private theorem two_pow_succ_sub_succ_div_two : (2 ^ (n+1) - (x + 1)) / 2 = 2^n - (x/2 + 1) := by
+  omega
+
+private theorem two_pow_succ_sub_one_div_two : (2 ^ (n+1) - 1) / 2 = 2^n - 1 :=
+  two_pow_succ_sub_succ_div_two
+
+private theorem two_mul_sub_one {n : Nat} (n_pos : n > 0) : (2*n - 1) % 2 = 1 := by
+  omega
+
+/-! ### Preliminaries -/
+
+/--
+An induction principal that works on divison by two.
+-/
+noncomputable def div2Induction {motive : Nat → Sort u}
+    (n : Nat) (ind : ∀(n : Nat), (n > 0 → motive (n/2)) → motive n) : motive n := by
+  induction n using Nat.strongInductionOn with
+  | ind n hyp =>
+    apply ind
+    intro n_pos
+    if n_eq : n = 0 then
+      simp [n_eq] at n_pos
+    else
+      apply hyp
+      exact Nat.div_lt_self n_pos (Nat.le_refl _)
+
+@[simp] theorem zero_and (x : Nat) : 0 &&& x = 0 := by rfl
+
+@[simp] theorem and_zero (x : Nat) : x &&& 0 = 0 := by
+  simp only [HAnd.hAnd, AndOp.and, land]
+  unfold bitwise
+  simp
+
+@[simp] theorem and_one_is_mod (x : Nat) : x &&& 1 = x % 2 := by
+  if xz : x = 0 then
+    simp [xz, zero_and]
+  else
+    have andz := and_zero (x/2)
+    simp only [HAnd.hAnd, AndOp.and, land] at andz
+    simp only [HAnd.hAnd, AndOp.and, land]
+    unfold bitwise
+    cases mod_two_eq_zero_or_one x with | _ p =>
+      simp [xz, p, andz, one_div_two, mod_eq_of_lt]
+
+/-! ### testBit -/
+
+@[simp] theorem zero_testBit (i : Nat) : testBit 0 i = false := by
+  simp only [testBit, zero_shiftRight, zero_and, bne_self_eq_false]
+
+@[simp] theorem testBit_zero (x : Nat) : testBit x 0 = decide (x % 2 = 1) := by
+  cases mod_two_eq_zero_or_one x with | _ p => simp [testBit, p]
+
+@[simp] theorem testBit_succ (x i : Nat) : testBit x (succ i) = testBit (x/2) i := by
+  unfold testBit
+  simp [shiftRight_succ_inside]
+
+theorem testBit_to_div_mod {x : Nat} : testBit x i = decide (x / 2^i % 2 = 1) := by
+  induction i generalizing x with
+  | zero =>
+    unfold testBit
+    cases mod_two_eq_zero_or_one x with | _ xz => simp [xz]
+  | succ i hyp =>
+    simp [hyp, Nat.div_div_eq_div_mul, Nat.pow_succ']
+
+theorem toNat_testBit (x i : Nat) :
+    (x.testBit i).toNat = x / 2 ^ i % 2 := by
+  rw [Nat.testBit_to_div_mod]
+  rcases Nat.mod_two_eq_zero_or_one (x / 2^i) <;> simp_all
+
+theorem ne_zero_implies_bit_true {x : Nat} (xnz : x ≠ 0) : ∃ i, testBit x i := by
+  induction x using div2Induction with
+  | ind x hyp =>
+    have x_pos : x > 0 := Nat.pos_of_ne_zero xnz
+    match mod_two_eq_zero_or_one x with
+    | Or.inl mod2_eq =>
+      rw [←div_add_mod x 2] at xnz
+      simp only [mod2_eq, ne_eq, Nat.mul_eq_zero, Nat.add_zero, false_or] at xnz
+      have ⟨d, dif⟩   := hyp x_pos xnz
+      apply Exists.intro (d+1)
+      simp_all
+    | Or.inr mod2_eq =>
+      apply Exists.intro 0
+      simp_all
+
+theorem ne_implies_bit_diff {x y : Nat} (p : x ≠ y) : ∃ i, testBit x i ≠ testBit y i := by
+  induction y using Nat.div2Induction generalizing x with
+  | ind y hyp =>
+    cases Nat.eq_zero_or_pos y with
+    | inl yz =>
+      simp only [yz, Nat.zero_testBit, Bool.eq_false_iff]
+      simp only [yz] at p
+      have ⟨i,ip⟩  := ne_zero_implies_bit_true p
+      apply Exists.intro i
+      simp [ip]
+    | inr ypos =>
+      if lsb_diff : x % 2 = y % 2 then
+        rw [←Nat.div_add_mod x 2, ←Nat.div_add_mod y 2] at p
+        simp only [ne_eq, lsb_diff, Nat.add_right_cancel_iff,
+          Nat.zero_lt_succ, Nat.mul_left_cancel_iff] at p
+        have ⟨i, ieq⟩  := hyp ypos p
+        apply Exists.intro (i+1)
+        simpa
+      else
+        apply Exists.intro 0
+        simp only [testBit_zero]
+        revert lsb_diff
+        cases mod_two_eq_zero_or_one x with | _ p =>
+          cases mod_two_eq_zero_or_one y with | _ q =>
+            simp [p,q]
+
+/--
+`eq_of_testBit_eq` allows proving two natural numbers are equal
+if their bits are all equal.
+-/
+theorem eq_of_testBit_eq {x y : Nat} (pred : ∀i, testBit x i = testBit y i) : x = y := by
+  if h : x = y then
+    exact h
+  else
+    let ⟨i,eq⟩ := ne_implies_bit_diff h
+    have p := pred i
+    contradiction
+
+theorem ge_two_pow_implies_high_bit_true {x : Nat} (p : x ≥ 2^n) : ∃ i, i ≥ n ∧ testBit x i := by
+  induction x using div2Induction generalizing n with
+  | ind x hyp =>
+    have x_pos : x > 0 := Nat.lt_of_lt_of_le (Nat.two_pow_pos n) p
+    have x_ne_zero : x ≠ 0 := Nat.ne_of_gt x_pos
+    match n with
+    | zero =>
+      let ⟨j, jp⟩ := ne_zero_implies_bit_true x_ne_zero
+      exact Exists.intro j (And.intro (Nat.zero_le _) jp)
+    | succ n =>
+      have x_ge_n : x / 2 ≥ 2 ^ n := by
+          simpa [le_div_iff_mul_le, ← Nat.pow_succ'] using p
+      have ⟨j, jp⟩ := @hyp x_pos n x_ge_n
+      apply Exists.intro (j+1)
+      apply And.intro
+      case left =>
+        exact (Nat.succ_le_succ jp.left)
+      case right =>
+        simpa using jp.right
+
+theorem testBit_implies_ge {x : Nat} (p : testBit x i = true) : x ≥ 2^i := by
+  simp only [testBit_to_div_mod] at p
+  apply Decidable.by_contra
+  intro not_ge
+  have x_lt : x < 2^i := Nat.lt_of_not_le not_ge
+  simp [div_eq_of_lt x_lt] at p
+
+theorem testBit_lt_two_pow {x i : Nat} (lt : x < 2^i) : x.testBit i = false := by
+  match p : x.testBit i with
+  | false => trivial
+  | true =>
+    exfalso
+    exact Nat.not_le_of_gt lt (testBit_implies_ge p)
+
+theorem lt_pow_two_of_testBit (x : Nat) (p : ∀i, i ≥ n → testBit x i = false) : x < 2^n := by
+  apply Decidable.by_contra
+  intro not_lt
+  have x_ge_n := Nat.ge_of_not_lt not_lt
+  have ⟨i, ⟨i_ge_n, test_true⟩⟩ := ge_two_pow_implies_high_bit_true x_ge_n
+  have test_false := p _ i_ge_n
+  simp only [test_true] at test_false
+
+/-! ### testBit -/
+
+private theorem succ_mod_two : succ x % 2 = 1 - x % 2 := by
+  induction x with
+  | zero =>
+    trivial
+  | succ x hyp =>
+    have p : 2 ≤ x + 2 := Nat.le_add_left _ _
+    simp [Nat.mod_eq (x+2) 2, p, hyp]
+    cases Nat.mod_two_eq_zero_or_one x with | _ p => simp [p]
+
+private theorem testBit_succ_zero : testBit (x + 1) 0 = not (testBit x 0) := by
+  simp [testBit_to_div_mod, succ_mod_two]
+  cases Nat.mod_two_eq_zero_or_one x with | _ p =>
+    simp [p]
+
+theorem testBit_two_pow_add_eq (x i : Nat) : testBit (2^i + x) i = not (testBit x i) := by
+  simp [testBit_to_div_mod, add_div_left, Nat.two_pow_pos, succ_mod_two]
+  cases mod_two_eq_zero_or_one (x / 2 ^ i) with
+  | _ p => simp [p]
+
+theorem testBit_mul_two_pow_add_eq (a b i : Nat) :
+    testBit (2^i*a + b) i = Bool.xor (a%2 = 1) (testBit b i) := by
+  match a with
+  | 0 => simp
+  | a+1 =>
+    simp [Nat.mul_succ, Nat.add_assoc,
+          testBit_mul_two_pow_add_eq a,
+          testBit_two_pow_add_eq,
+          Nat.succ_mod_two]
+    cases mod_two_eq_zero_or_one a with
+    | _ p => simp [p]
+
+theorem testBit_two_pow_add_gt {i j : Nat} (j_lt_i : j < i) (x : Nat) :
+    testBit (2^i + x) j = testBit x j := by
+  have i_def : i = j + (i-j) := (Nat.add_sub_cancel' (Nat.le_of_lt j_lt_i)).symm
+  rw [i_def]
+  simp only [testBit_to_div_mod, Nat.pow_add,
+        Nat.add_comm x, Nat.mul_add_div (Nat.two_pow_pos _)]
+  match i_sub_j_eq : i - j with
+  | 0 =>
+    exfalso
+    rw [Nat.sub_eq_zero_iff_le] at i_sub_j_eq
+    exact Nat.not_le_of_gt j_lt_i i_sub_j_eq
+  | d+1 =>
+    simp [Nat.pow_succ, Nat.mul_comm _ 2,  Nat.mul_add_mod]
+
+@[simp] theorem testBit_mod_two_pow (x j i : Nat) :
+    testBit (x % 2^j) i = (decide (i < j) && testBit x i) := by
+  induction x using Nat.strongInductionOn generalizing j i with
+  | ind x hyp =>
+    rw [mod_eq]
+    rcases Nat.lt_or_ge x (2^j) with x_lt_j | x_ge_j
+    · have not_j_le_x := Nat.not_le_of_gt x_lt_j
+      simp [not_j_le_x]
+      rcases Nat.lt_or_ge i j with i_lt_j | i_ge_j
+      · simp [i_lt_j]
+      · have x_lt : x < 2^i :=
+            calc x < 2^j := x_lt_j
+                _ ≤ 2^i := Nat.pow_le_pow_of_le_right Nat.zero_lt_two i_ge_j
+        simp [Nat.testBit_lt_two_pow x_lt]
+    · generalize y_eq : x - 2^j = y
+      have x_eq : x = y + 2^j := Nat.eq_add_of_sub_eq x_ge_j y_eq
+      simp only [Nat.two_pow_pos, x_eq, Nat.le_add_left, true_and, ite_true]
+      have y_lt_x : y < x := by
+            simp [x_eq]
+            exact Nat.lt_add_of_pos_right (Nat.two_pow_pos j)
+      simp only [hyp y y_lt_x]
+      if i_lt_j : i < j then
+        rw [ Nat.add_comm _ (2^_), testBit_two_pow_add_gt i_lt_j]
+      else
+        simp [i_lt_j]
+
+theorem testBit_one_zero : testBit 1 0 = true := by trivial
+
+theorem not_decide_mod_two_eq_one (x : Nat)
+    : (!decide (x % 2 = 1)) = decide (x % 2 = 0) := by
+  cases Nat.mod_two_eq_zero_or_one x <;> (rename_i p; simp [p])
+
+theorem testBit_two_pow_sub_succ (h₂ : x < 2 ^ n) (i : Nat) :
+    testBit (2^n - (x + 1)) i = (decide (i < n) && ! testBit x i) := by
+  induction i generalizing n x with
+  | zero =>
+    match n with
+    | 0 => simp [succ_sub_succ_eq_sub]
+    | n+1 =>
+      simp [not_decide_mod_two_eq_one]
+      omega
+  | succ i ih =>
+    simp only [testBit_succ]
+    match n with
+    | 0 =>
+      simp [decide_eq_false, succ_sub_succ_eq_sub]
+    | n+1 =>
+      rw [Nat.two_pow_succ_sub_succ_div_two, ih]
+      · simp [Nat.succ_lt_succ_iff]
+      · omega
+
+@[simp] theorem testBit_two_pow_sub_one (n i : Nat) : testBit (2^n-1) i = decide (i < n) := by
+  rw [testBit_two_pow_sub_succ]
+  · simp
+  · exact Nat.two_pow_pos _
+
+theorem testBit_bool_to_nat (b : Bool) (i : Nat) :
+    testBit (Bool.toNat b) i = (decide (i = 0) && b) := by
+  cases b <;> cases i <;>
+  simp [testBit_to_div_mod, Nat.pow_succ, Nat.mul_comm _ 2,
+        ←Nat.div_div_eq_div_mul _ 2, one_div_two,
+        Nat.mod_eq_of_lt]
+
+/-! ### bitwise -/
+
+theorem testBit_bitwise
+  (false_false_axiom : f false false = false) (x y i : Nat)
+: (bitwise f x y).testBit i = f (x.testBit i) (y.testBit i) := by
+  induction i using Nat.strongInductionOn generalizing x y with
+  | ind i hyp =>
+    unfold bitwise
+    if x_zero : x = 0 then
+      cases p : f false true <;>
+        cases yi : testBit y i <;>
+          simp [x_zero, p, yi, false_false_axiom]
+    else if y_zero : y = 0 then
+      simp [x_zero, y_zero]
+      cases p : f true false <;>
+        cases xi : testBit x i <;>
+          simp [p, xi, false_false_axiom]
+    else
+      simp only [x_zero, y_zero, ←Nat.two_mul]
+      cases i with
+      | zero =>
+        cases p : f (decide (x % 2 = 1)) (decide (y % 2 = 1)) <;>
+          simp [p, Nat.mul_add_mod, mod_eq_of_lt]
+      | succ i =>
+        have hyp_i := hyp i (Nat.le_refl (i+1))
+        cases p : f (decide (x % 2 = 1)) (decide (y % 2 = 1)) <;>
+          simp [p, one_div_two, hyp_i, Nat.mul_add_div]
+
+/-! ### bitwise -/
+
+@[local simp]
+private theorem eq_0_of_lt_one (x : Nat) : x < 1 ↔ x = 0 :=
+  Iff.intro
+    (fun p =>
+      match x with
+      | 0 => Eq.refl 0
+      | _+1 => False.elim (not_lt_zero _ (Nat.lt_of_succ_lt_succ p)))
+    (fun p => by simp [p])
+
+private theorem eq_0_of_lt (x : Nat) : x < 2^ 0 ↔ x = 0 := eq_0_of_lt_one x
+
+@[local simp]
+private theorem zero_lt_pow (n : Nat) : 0 < 2^n := by
+  induction n
+  case zero => simp [eq_0_of_lt]
+  case succ n hyp => simpa [Nat.pow_succ]
+
+private theorem div_two_le_of_lt_two {m n : Nat} (p : m < 2 ^ succ n) : m / 2 < 2^n := by
+  simp [div_lt_iff_lt_mul Nat.zero_lt_two]
+  exact p
+
+/-- This provides a bound on bitwise operations. -/
+theorem bitwise_lt_two_pow (left : x < 2^n) (right : y < 2^n) : (Nat.bitwise f x y) < 2^n := by
+  induction n generalizing x y with
+  | zero =>
+    simp only [eq_0_of_lt] at left right
+    unfold bitwise
+    simp [left, right]
+  | succ n hyp =>
+    unfold bitwise
+    if x_zero : x = 0 then
+      simp only [x_zero, if_pos]
+      by_cases p : f false true = true <;> simp [p, right]
+    else if y_zero : y = 0 then
+      simp only [x_zero, y_zero, if_neg, if_pos]
+      by_cases p : f true false = true <;> simp [p, left]
+    else
+      simp only [x_zero, y_zero, if_neg]
+      have hyp1 := hyp (div_two_le_of_lt_two left) (div_two_le_of_lt_two right)
+      by_cases p : f (decide (x % 2 = 1)) (decide (y % 2 = 1)) = true <;>
+        simp [p, Nat.pow_succ, mul_succ, Nat.add_assoc]
+      case pos =>
+        apply lt_of_succ_le
+        simp only [← Nat.succ_add]
+        apply Nat.add_le_add <;> exact hyp1
+      case neg =>
+        apply Nat.add_lt_add <;> exact hyp1
+
+/-! ### and -/
+
+@[simp] theorem testBit_and (x y i : Nat) : (x &&& y).testBit i = (x.testBit i && y.testBit i) := by
+  simp [HAnd.hAnd, AndOp.and, land, testBit_bitwise ]
+
+theorem and_lt_two_pow (x : Nat) {y n : Nat} (right : y < 2^n) : (x &&& y) < 2^n := by
+  apply lt_pow_two_of_testBit
+  intro i i_ge_n
+  have yf : testBit y i = false := by
+          apply Nat.testBit_lt_two_pow
+          apply Nat.lt_of_lt_of_le right
+          exact pow_le_pow_of_le_right Nat.zero_lt_two i_ge_n
+  simp [testBit_and, yf]
+
+@[simp] theorem and_pow_two_is_mod (x n : Nat) : x &&& (2^n-1) = x % 2^n := by
+  apply eq_of_testBit_eq
+  intro i
+  simp only [testBit_and, testBit_mod_two_pow]
+  cases testBit x i <;> simp
+
+theorem and_pow_two_identity {x : Nat} (lt : x < 2^n) : x &&& 2^n-1 = x := by
+  rw [and_pow_two_is_mod]
+  apply Nat.mod_eq_of_lt lt
+
+/-! ### lor -/
+
+@[simp] theorem or_zero (x : Nat) : 0 ||| x = x := by
+  simp only [HOr.hOr, OrOp.or, lor]
+  unfold bitwise
+  simp [@eq_comm _ 0]
+
+@[simp] theorem zero_or (x : Nat) : x ||| 0 = x := by
+  simp only [HOr.hOr, OrOp.or, lor]
+  unfold bitwise
+  simp [@eq_comm _ 0]
+
+@[simp] theorem testBit_or (x y i : Nat) : (x ||| y).testBit i = (x.testBit i || y.testBit i) := by
+  simp [HOr.hOr, OrOp.or, lor, testBit_bitwise ]
+
+theorem or_lt_two_pow {x y n : Nat} (left : x < 2^n) (right : y < 2^n) : x ||| y < 2^n :=
+  bitwise_lt_two_pow left right
+
+/-! ### xor -/
+
+@[simp] theorem testBit_xor (x y i : Nat) :
+    (x ^^^ y).testBit i = Bool.xor (x.testBit i) (y.testBit i) := by
+  simp [HXor.hXor, Xor.xor, xor, testBit_bitwise ]
+
+theorem xor_lt_two_pow {x y n : Nat} (left : x < 2^n) (right : y < 2^n) : x ^^^ y < 2^n :=
+  bitwise_lt_two_pow left right
+
+/-! ### Arithmetic -/
+
+theorem testBit_mul_pow_two_add (a : Nat) {b i : Nat} (b_lt : b < 2^i) (j : Nat) :
+    testBit (2 ^ i * a + b) j =
+      if j < i then
+        testBit b j
+      else
+        testBit a (j - i) := by
+  cases Nat.lt_or_ge j i with
+  | inl j_lt =>
+    simp only [j_lt]
+    have i_def : i = j + succ (pred (i-j)) := by
+      rw [succ_pred_eq_of_pos] <;> omega
+    rw [i_def]
+    simp only [testBit_to_div_mod, Nat.pow_add, Nat.mul_assoc]
+    simp only [Nat.mul_add_div (Nat.two_pow_pos _), Nat.mul_add_mod]
+    simp [Nat.pow_succ, Nat.mul_comm _ 2, Nat.mul_assoc, Nat.mul_add_mod]
+  | inr j_ge =>
+    have j_def : j = i + (j-i) := (Nat.add_sub_cancel' j_ge).symm
+    simp only [
+        testBit_to_div_mod,
+        Nat.not_lt_of_le,
+        j_ge,
+        ite_false]
+    simp [congrArg (2^·) j_def, Nat.pow_add,
+          ←Nat.div_div_eq_div_mul,
+          Nat.mul_add_div,
+          Nat.div_eq_of_lt b_lt,
+          Nat.two_pow_pos i]
+
+theorem testBit_mul_pow_two :
+    testBit (2 ^ i * a) j = (decide (j ≥ i) && testBit a (j-i)) := by
+  have gen := testBit_mul_pow_two_add a (Nat.two_pow_pos i) j
+  simp at gen
+  rw [gen]
+  cases Nat.lt_or_ge j i with
+  | _ p => simp [p, Nat.not_le_of_lt, Nat.not_lt_of_le]
+
+theorem mul_add_lt_is_or {b : Nat} (b_lt : b < 2^i) (a : Nat) : 2^i * a + b = 2^i * a ||| b := by
+  apply eq_of_testBit_eq
+  intro j
+  simp only [testBit_mul_pow_two_add _ b_lt,
+        testBit_or, testBit_mul_pow_two]
+  if j_lt : j < i then
+    simp [Nat.not_le_of_lt, j_lt]
+  else
+    have i_le : i ≤ j := Nat.le_of_not_lt j_lt
+    have b_lt_j :=
+            calc b < 2 ^ i := b_lt
+                 _ ≤ 2 ^ j := Nat.pow_le_pow_of_le_right Nat.zero_lt_two i_le
+    simp [i_le, j_lt, testBit_lt_two_pow, b_lt_j]
+
+/-! ### shiftLeft and shiftRight -/
+
+@[simp] theorem testBit_shiftLeft (x : Nat) : testBit (x <<< i) j =
+    (decide (j ≥ i) && testBit x (j-i)) := by
+  simp [shiftLeft_eq, Nat.mul_comm _ (2^_), testBit_mul_pow_two]
+
+@[simp] theorem testBit_shiftRight (x : Nat) : testBit (x >>> i) j = testBit x (i+j) := by
+  simp [testBit, ←shiftRight_add]

src/Init/Data/Nat/Compare.lean

@@ -0,0 +1,57 @@
+/-
+Copyright (c) 2016 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Leonardo de Moura, Jeremy Avigad, Mario Carneiro
+-/
+prelude
+import Init.Classical
+import Init.Data.Ord
+
+/-! # Basic lemmas about comparing natural numbers
+
+This file introduce some basic lemmas about compare as applied to natural
+numbers.
+-/
+namespace Nat
+
+theorem compare_def_lt (a b : Nat) :
+    compare a b = if a < b then .lt else if b < a then .gt else .eq := by
+  simp only [compare, compareOfLessAndEq]
+  split
+  · rfl
+  · next h =>
+    match Nat.lt_or_eq_of_le (Nat.not_lt.1 h) with
+    | .inl h => simp [h, Nat.ne_of_gt h]
+    | .inr rfl => simp
+
+theorem compare_def_le (a b : Nat) :
+    compare a b = if a ≤ b then if b ≤ a then .eq else .lt else .gt := by
+  rw [compare_def_lt]
+  split
+  · next hlt => simp [Nat.le_of_lt hlt, Nat.not_le.2 hlt]
+  · next hge =>
+    split
+    · next hgt => simp [Nat.le_of_lt hgt, Nat.not_le.2 hgt]
+    · next hle => simp [Nat.not_lt.1 hge, Nat.not_lt.1 hle]
+
+protected theorem compare_swap (a b : Nat) : (compare a b).swap = compare b a := by
+  simp only [compare_def_le]; (repeat' split) <;> try rfl
+  next h1 h2 => cases h1 (Nat.le_of_not_le h2)
+
+protected theorem compare_eq_eq {a b : Nat} : compare a b = .eq ↔ a = b := by
+  rw [compare_def_lt]; (repeat' split) <;> simp [Nat.ne_of_lt, Nat.ne_of_gt, *]
+  next hlt hgt => exact Nat.le_antisymm (Nat.not_lt.1 hgt) (Nat.not_lt.1 hlt)
+
+protected theorem compare_eq_lt {a b : Nat} : compare a b = .lt ↔ a < b := by
+  rw [compare_def_lt]; (repeat' split) <;> simp [*]
+
+protected theorem compare_eq_gt {a b : Nat} : compare a b = .gt ↔ b < a := by
+  rw [compare_def_lt]; (repeat' split) <;> simp [Nat.le_of_lt, *]
+
+protected theorem compare_ne_gt {a b : Nat} : compare a b ≠ .gt ↔ a ≤ b := by
+  rw [compare_def_le]; (repeat' split) <;> simp [*]
+
+protected theorem compare_ne_lt {a b : Nat} : compare a b ≠ .lt ↔ b ≤ a := by
+  rw [compare_def_le]; (repeat' split) <;> simp [Nat.le_of_not_le, *]
+
+end Nat

src/Init/Data/Nat/Div.lean

@@ -7,8 +7,16 @@ prelude
 import Init.WF
 import Init.WFTactics
 import Init.Data.Nat.Basic
+
 namespace Nat
 
+/--
+Divisibility of natural numbers. `a ∣ b` (typed as `\|`) says that
+there is some `c` such that `b = a * c`.
+-/
+instance : Dvd Nat where
+  dvd a b := Exists (fun c => b = a * c)
+
 theorem div_rec_lemma {x y : Nat} : 0 < y ∧ y ≤ x → x - y < x :=
   fun ⟨ypos, ylex⟩ => sub_lt (Nat.lt_of_lt_of_le ypos ylex) ypos
 
@@ -20,14 +28,14 @@ protected def div (x y : @& Nat) : Nat :=
     0
 decreasing_by apply div_rec_lemma; assumption
 
-instance : Div Nat := ⟨Nat.div⟩
+instance instDiv : Div Nat := ⟨Nat.div⟩
 
 theorem div_eq (x y : Nat) : x / y = if 0 < y ∧ y ≤ x then (x - y) / y + 1 else 0 := by
   show Nat.div x y = _
   rw [Nat.div]
   rfl
 
-theorem div.inductionOn.{u}
+def div.inductionOn.{u}
       {motive : Nat → Nat → Sort u}
       (x y : Nat)
       (ind  : ∀ x y, 0 < y ∧ y ≤ x → motive (x - y) y → motive x y)
@@ -82,7 +90,7 @@ protected def mod : @& Nat → @& Nat → Nat
   | 0, _ => 0
   | x@(_ + 1), y => Nat.modCore x y
 
-instance : Mod Nat := ⟨Nat.mod⟩
+instance instMod : Mod Nat := ⟨Nat.mod⟩
 
 protected theorem modCore_eq_mod (x y : Nat) : Nat.modCore x y = x % y := by
   cases x with
@@ -94,7 +102,7 @@ protected theorem modCore_eq_mod (x y : Nat) : Nat.modCore x y = x % y := by
 theorem mod_eq (x y : Nat) : x % y = if 0 < y ∧ y ≤ x then (x - y) % y else x := by
   rw [←Nat.modCore_eq_mod, ←Nat.modCore_eq_mod, Nat.modCore]
 
-theorem mod.inductionOn.{u}
+def mod.inductionOn.{u}
       {motive : Nat → Nat → Sort u}
       (x y  : Nat)
       (ind  : ∀ x y, 0 < y ∧ y ≤ x → motive (x - y) y → motive x y)
@@ -174,4 +182,202 @@ theorem div_add_mod (m n : Nat) : n * (m / n) + m % n = m := by
     rw [Nat.left_distrib, Nat.mul_one, Nat.add_assoc, Nat.add_left_comm, ih, Nat.add_comm, Nat.sub_add_cancel h.2]
 decreasing_by apply div_rec_lemma; assumption
 
+theorem div_eq_sub_div (h₁ : 0 < b) (h₂ : b ≤ a) : a / b = (a - b) / b + 1 := by
+ rw [div_eq a, if_pos]; constructor <;> assumption
+
+
+theorem mod_add_div (m k : Nat) : m % k + k * (m / k) = m := by
+  induction m, k using mod.inductionOn with rw [div_eq, mod_eq]
+  | base x y h => simp [h]
+  | ind x y h IH => simp [h]; rw [Nat.mul_succ, ← Nat.add_assoc, IH, Nat.sub_add_cancel h.2]
+
+@[simp] protected theorem div_one (n : Nat) : n / 1 = n := by
+  have := mod_add_div n 1
+  rwa [mod_one, Nat.zero_add, Nat.one_mul] at this
+
+@[simp] protected theorem div_zero (n : Nat) : n / 0 = 0 := by
+  rw [div_eq]; simp [Nat.lt_irrefl]
+
+@[simp] protected theorem zero_div (b : Nat) : 0 / b = 0 :=
+  (div_eq 0 b).trans <| if_neg <| And.rec Nat.not_le_of_gt
+
+theorem le_div_iff_mul_le (k0 : 0 < k) : x ≤ y / k ↔ x * k ≤ y := by
+  induction y, k using mod.inductionOn generalizing x with
+    (rw [div_eq]; simp [h]; cases x with | zero => simp [zero_le] | succ x => ?_)
+  | base y k h =>
+    simp only [add_one, succ_mul, false_iff, Nat.not_le]
+    refine Nat.lt_of_lt_of_le ?_ (Nat.le_add_left ..)
+    exact Nat.not_le.1 fun h' => h ⟨k0, h'⟩
+  | ind y k h IH =>
+    rw [Nat.add_le_add_iff_right, IH k0, succ_mul,
+        ← Nat.add_sub_cancel (x*k) k, Nat.sub_le_sub_iff_right h.2, Nat.add_sub_cancel]
+
+protected theorem div_div_eq_div_mul (m n k : Nat) : m / n / k = m / (n * k) := by
+  cases eq_zero_or_pos k with
+  | inl k0 => rw [k0, Nat.mul_zero, Nat.div_zero, Nat.div_zero] | inr kpos => ?_
+  cases eq_zero_or_pos n with
+  | inl n0 => rw [n0, Nat.zero_mul, Nat.div_zero, Nat.zero_div] | inr npos => ?_
+
+  apply Nat.le_antisymm
+
+  apply (le_div_iff_mul_le (Nat.mul_pos npos kpos)).2
+  rw [Nat.mul_comm n k, ← Nat.mul_assoc]
+  apply (le_div_iff_mul_le npos).1
+  apply (le_div_iff_mul_le kpos).1
+  (apply Nat.le_refl)
+
+  apply (le_div_iff_mul_le kpos).2
+  apply (le_div_iff_mul_le npos).2
+  rw [Nat.mul_assoc, Nat.mul_comm n k]
+  apply (le_div_iff_mul_le (Nat.mul_pos kpos npos)).1
+  apply Nat.le_refl
+
+theorem div_mul_le_self : ∀ (m n : Nat), m / n * n ≤ m
+  | m, 0   => by simp
+  | m, n+1 => (le_div_iff_mul_le (Nat.succ_pos _)).1 (Nat.le_refl _)
+
+theorem div_lt_iff_lt_mul (Hk : 0 < k) : x / k < y ↔ x < y * k := by
+  rw [← Nat.not_le, ← Nat.not_le]; exact not_congr (le_div_iff_mul_le Hk)
+
+@[simp] theorem add_div_right (x : Nat) {z : Nat} (H : 0 < z) : (x + z) / z = succ (x / z) := by
+  rw [div_eq_sub_div H (Nat.le_add_left _ _), Nat.add_sub_cancel]
+
+@[simp] theorem add_div_left (x : Nat) {z : Nat} (H : 0 < z) : (z + x) / z = succ (x / z) := by
+  rw [Nat.add_comm, add_div_right x H]
+
+theorem add_mul_div_left (x z : Nat) {y : Nat} (H : 0 < y) : (x + y * z) / y = x / y + z := by
+  induction z with
+  | zero => rw [Nat.mul_zero, Nat.add_zero, Nat.add_zero]
+  | succ z ih => rw [mul_succ, ← Nat.add_assoc, add_div_right _ H, ih]; rfl
+
+theorem add_mul_div_right (x y : Nat) {z : Nat} (H : 0 < z) : (x + y * z) / z = x / z + y := by
+  rw [Nat.mul_comm, add_mul_div_left _ _ H]
+
+@[simp] theorem add_mod_right (x z : Nat) : (x + z) % z = x % z := by
+  rw [mod_eq_sub_mod (Nat.le_add_left ..), Nat.add_sub_cancel]
+
+@[simp] theorem add_mod_left (x z : Nat) : (x + z) % x = z % x := by
+  rw [Nat.add_comm, add_mod_right]
+
+@[simp] theorem add_mul_mod_self_left (x y z : Nat) : (x + y * z) % y = x % y := by
+  match z with
+  | 0 => rw [Nat.mul_zero, Nat.add_zero]
+  | succ z => rw [mul_succ, ← Nat.add_assoc, add_mod_right, add_mul_mod_self_left (z := z)]
+
+@[simp] theorem add_mul_mod_self_right (x y z : Nat) : (x + y * z) % z = x % z := by
+  rw [Nat.mul_comm, add_mul_mod_self_left]
+
+@[simp] theorem mul_mod_right (m n : Nat) : (m * n) % m = 0 := by
+  rw [← Nat.zero_add (m * n), add_mul_mod_self_left, zero_mod]
+
+@[simp] theorem mul_mod_left (m n : Nat) : (m * n) % n = 0 := by
+  rw [Nat.mul_comm, mul_mod_right]
+
+protected theorem div_eq_of_lt_le (lo : k * n ≤ m) (hi : m < succ k * n) : m / n = k :=
+have npos : 0 < n := (eq_zero_or_pos _).resolve_left fun hn => by
+  rw [hn, Nat.mul_zero] at hi lo; exact absurd lo (Nat.not_le_of_gt hi)
+Nat.le_antisymm
+  (le_of_lt_succ ((Nat.div_lt_iff_lt_mul npos).2 hi))
+  ((Nat.le_div_iff_mul_le npos).2 lo)
+
+theorem sub_mul_div (x n p : Nat) (h₁ : n*p ≤ x) : (x - n*p) / n = x / n - p := by
+  match eq_zero_or_pos n with
+  | .inl h₀ => rw [h₀, Nat.div_zero, Nat.div_zero, Nat.zero_sub]
+  | .inr h₀ => induction p with
+    | zero => rw [Nat.mul_zero, Nat.sub_zero, Nat.sub_zero]
+    | succ p IH =>
+      have h₂ : n * p ≤ x := Nat.le_trans (Nat.mul_le_mul_left _ (le_succ _)) h₁
+      have h₃ : x - n * p ≥ n := by
+        apply Nat.le_of_add_le_add_right
+        rw [Nat.sub_add_cancel h₂, Nat.add_comm]
+        rw [mul_succ] at h₁
+        exact h₁
+      rw [sub_succ, ← IH h₂, div_eq_sub_div h₀ h₃]
+      simp [Nat.pred_succ, mul_succ, Nat.sub_sub]
+
+theorem mul_sub_div (x n p : Nat) (h₁ : x < n*p) : (n * p - succ x) / n = p - succ (x / n) := by
+  have npos : 0 < n := (eq_zero_or_pos _).resolve_left fun n0 => by
+    rw [n0, Nat.zero_mul] at h₁; exact not_lt_zero _ h₁
+  apply Nat.div_eq_of_lt_le
+  focus
+    rw [Nat.mul_sub_right_distrib, Nat.mul_comm]
+    exact Nat.sub_le_sub_left ((div_lt_iff_lt_mul npos).1 (lt_succ_self _)) _
+  focus
+    show succ (pred (n * p - x)) ≤ (succ (pred (p - x / n))) * n
+    rw [succ_pred_eq_of_pos (Nat.sub_pos_of_lt h₁),
+      fun h => succ_pred_eq_of_pos (Nat.sub_pos_of_lt h)] -- TODO: why is the function needed?
+    focus
+      rw [Nat.mul_sub_right_distrib, Nat.mul_comm]
+      exact Nat.sub_le_sub_left (div_mul_le_self ..) _
+    focus
+      rwa [div_lt_iff_lt_mul npos, Nat.mul_comm]
+
+theorem mul_mod_mul_left (z x y : Nat) : (z * x) % (z * y) = z * (x % y) :=
+  if y0 : y = 0 then by
+    rw [y0, Nat.mul_zero, mod_zero, mod_zero]
+  else if z0 : z = 0 then by
+    rw [z0, Nat.zero_mul, Nat.zero_mul, Nat.zero_mul, mod_zero]
+  else by
+    induction x using Nat.strongInductionOn with
+    | _ n IH =>
+      have y0 : y > 0 := Nat.pos_of_ne_zero y0
+      have z0 : z > 0 := Nat.pos_of_ne_zero z0
+      cases Nat.lt_or_ge n y with
+      | inl yn => rw [mod_eq_of_lt yn, mod_eq_of_lt (Nat.mul_lt_mul_of_pos_left yn z0)]
+      | inr yn =>
+        rw [mod_eq_sub_mod yn, mod_eq_sub_mod (Nat.mul_le_mul_left z yn),
+          ← Nat.mul_sub_left_distrib]
+        exact IH _ (sub_lt (Nat.lt_of_lt_of_le y0 yn) y0)
+
+theorem div_eq_of_lt (h₀ : a < b) : a / b = 0 := by
+  rw [div_eq a, if_neg]
+  intro h₁
+  apply Nat.not_le_of_gt h₀ h₁.right
+
+protected theorem mul_div_cancel (m : Nat) {n : Nat} (H : 0 < n) : m * n / n = m := by
+  let t := add_mul_div_right 0 m H
+  rwa [Nat.zero_add, Nat.zero_div, Nat.zero_add] at t
+
+protected theorem mul_div_cancel_left (m : Nat) {n : Nat} (H : 0 < n) : n * m / n = m := by
+  rw [Nat.mul_comm, Nat.mul_div_cancel _ H]
+
+protected theorem div_le_of_le_mul {m n : Nat} : ∀ {k}, m ≤ k * n → m / k ≤ n
+  | 0, _ => by simp [Nat.div_zero, n.zero_le]
+  | succ k, h => by
+    suffices succ k * (m / succ k) ≤ succ k * n from
+      Nat.le_of_mul_le_mul_left this (zero_lt_succ _)
+    have h1 : succ k * (m / succ k) ≤ m % succ k + succ k * (m / succ k) := Nat.le_add_left _ _
+    have h2 : m % succ k + succ k * (m / succ k) = m := by rw [mod_add_div]
+    have h3 : m ≤ succ k * n := h
+    rw [← h2] at h3
+    exact Nat.le_trans h1 h3
+
+@[simp] theorem mul_div_right (n : Nat) {m : Nat} (H : 0 < m) : m * n / m = n := by
+  induction n <;> simp_all [mul_succ]
+
+@[simp] theorem mul_div_left (m : Nat) {n : Nat} (H : 0 < n) : m * n / n = m := by
+  rw [Nat.mul_comm, mul_div_right _ H]
+
+protected theorem div_self (H : 0 < n) : n / n = 1 := by
+  let t := add_div_right 0 H
+  rwa [Nat.zero_add, Nat.zero_div] at t
+
+protected theorem div_eq_of_eq_mul_left (H1 : 0 < n) (H2 : m = k * n) : m / n = k :=
+by rw [H2, Nat.mul_div_cancel _ H1]
+
+protected theorem div_eq_of_eq_mul_right (H1 : 0 < n) (H2 : m = n * k) : m / n = k :=
+by rw [H2, Nat.mul_div_cancel_left _ H1]
+
+protected theorem mul_div_mul_left {m : Nat} (n k : Nat) (H : 0 < m) :
+    m * n / (m * k) = n / k := by rw [← Nat.div_div_eq_div_mul, Nat.mul_div_cancel_left _ H]
+
+protected theorem mul_div_mul_right {m : Nat} (n k : Nat) (H : 0 < m) :
+    n * m / (k * m) = n / k := by rw [Nat.mul_comm, Nat.mul_comm k, Nat.mul_div_mul_left _ _ H]
+
+theorem mul_div_le (m n : Nat) : n * (m / n) ≤ m := by
+  match n, Nat.eq_zero_or_pos n with
+  | _, Or.inl rfl => rw [Nat.zero_mul]; exact m.zero_le
+  | n, Or.inr h => rw [Nat.mul_comm, ← Nat.le_div_iff_mul_le h]; exact Nat.le_refl _
+
+
 end Nat

src/Init/Data/Nat/Dvd.lean

@@ -0,0 +1,132 @@
+/-
+Copyright (c) 2016 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Leonardo de Moura, Jeremy Avigad, Mario Carneiro
+-/
+prelude
+import Init.Data.Nat.Div
+import Init.Meta
+
+namespace Nat
+
+protected theorem dvd_refl (a : Nat) : a ∣ a := ⟨1, by simp⟩
+
+protected theorem dvd_zero (a : Nat) : a ∣ 0 := ⟨0, by simp⟩
+
+protected theorem dvd_mul_left (a b : Nat) : a ∣ b * a := ⟨b, Nat.mul_comm b a⟩
+protected theorem dvd_mul_right (a b : Nat) : a ∣ a * b := ⟨b, rfl⟩
+
+protected theorem dvd_trans {a b c : Nat} (h₁ : a ∣ b) (h₂ : b ∣ c) : a ∣ c :=
+  match h₁, h₂ with
+  | ⟨d, (h₃ : b = a * d)⟩, ⟨e, (h₄ : c = b * e)⟩ =>
+    ⟨d * e, show c = a * (d * e) by simp[h₃,h₄, Nat.mul_assoc]⟩
+
+protected theorem eq_zero_of_zero_dvd {a : Nat} (h : 0 ∣ a) : a = 0 :=
+  let ⟨c, H'⟩ := h; H'.trans c.zero_mul
+
+@[simp] protected theorem zero_dvd {n : Nat} : 0 ∣ n ↔ n = 0 :=
+  ⟨Nat.eq_zero_of_zero_dvd, fun h => h.symm ▸ Nat.dvd_zero 0⟩
+
+protected theorem dvd_add {a b c : Nat} (h₁ : a ∣ b) (h₂ : a ∣ c) : a ∣ b + c :=
+  let ⟨d, hd⟩ := h₁; let ⟨e, he⟩ := h₂; ⟨d + e, by simp [Nat.left_distrib, hd, he]⟩
+
+protected theorem dvd_add_iff_right {k m n : Nat} (h : k ∣ m) : k ∣ n ↔ k ∣ m + n :=
+  ⟨Nat.dvd_add h,
+    match m, h with
+    | _, ⟨d, rfl⟩ => fun ⟨e, he⟩ =>
+      ⟨e - d, by rw [Nat.mul_sub_left_distrib, ← he, Nat.add_sub_cancel_left]⟩⟩
+
+protected theorem dvd_add_iff_left {k m n : Nat} (h : k ∣ n) : k ∣ m ↔ k ∣ m + n := by
+  rw [Nat.add_comm]; exact Nat.dvd_add_iff_right h
+
+theorem dvd_mod_iff {k m n : Nat} (h: k ∣ n) : k ∣ m % n ↔ k ∣ m :=
+  have := Nat.dvd_add_iff_left <| Nat.dvd_trans h <| Nat.dvd_mul_right n (m / n)
+  by rwa [mod_add_div] at this
+
+theorem le_of_dvd {m n : Nat} (h : 0 < n) : m ∣ n → m ≤ n
+  | ⟨k, e⟩ => by
+    revert h
+    rw [e]
+    match k with
+    | 0 => intro hn; simp at hn
+    | pk+1 =>
+      intro
+      have := Nat.mul_le_mul_left m (succ_pos pk)
+      rwa [Nat.mul_one] at this
+
+protected theorem dvd_antisymm : ∀ {m n : Nat}, m ∣ n → n ∣ m → m = n
+  | _, 0, _, h₂ => Nat.eq_zero_of_zero_dvd h₂
+  | 0, _, h₁, _ => (Nat.eq_zero_of_zero_dvd h₁).symm
+  | _+1, _+1, h₁, h₂ => Nat.le_antisymm (le_of_dvd (succ_pos _) h₁) (le_of_dvd (succ_pos _) h₂)
+
+theorem pos_of_dvd_of_pos {m n : Nat} (H1 : m ∣ n) (H2 : 0 < n) : 0 < m :=
+  Nat.pos_of_ne_zero fun m0 => Nat.ne_of_gt H2 <| Nat.eq_zero_of_zero_dvd (m0 ▸ H1)
+
+@[simp] protected theorem one_dvd (n : Nat) : 1 ∣ n := ⟨n, n.one_mul.symm⟩
+
+theorem eq_one_of_dvd_one {n : Nat} (H : n ∣ 1) : n = 1 := Nat.dvd_antisymm H n.one_dvd
+
+theorem mod_eq_zero_of_dvd {m n : Nat} (H : m ∣ n) : n % m = 0 := by
+  let ⟨z, H⟩ := H; rw [H, mul_mod_right]
+
+theorem dvd_of_mod_eq_zero {m n : Nat} (H : n % m = 0) : m ∣ n := by
+  exists n / m
+  have := (mod_add_div n m).symm
+  rwa [H, Nat.zero_add] at this
+
+theorem dvd_iff_mod_eq_zero (m n : Nat) : m ∣ n ↔ n % m = 0 :=
+  ⟨mod_eq_zero_of_dvd, dvd_of_mod_eq_zero⟩
+
+instance decidable_dvd : @DecidableRel Nat (·∣·) :=
+  fun _ _ => decidable_of_decidable_of_iff (dvd_iff_mod_eq_zero _ _).symm
+
+theorem emod_pos_of_not_dvd {a b : Nat} (h : ¬ a ∣ b) : 0 < b % a := by
+  rw [dvd_iff_mod_eq_zero] at h
+  exact Nat.pos_of_ne_zero h
+
+protected theorem mul_div_cancel' {n m : Nat} (H : n ∣ m) : n * (m / n) = m := by
+  have := mod_add_div m n
+  rwa [mod_eq_zero_of_dvd H, Nat.zero_add] at this
+
+protected theorem div_mul_cancel {n m : Nat} (H : n ∣ m) : m / n * n = m := by
+  rw [Nat.mul_comm, Nat.mul_div_cancel' H]
+
+@[simp] theorem mod_mod_of_dvd (a : Nat) (h : c ∣ b) : a % b % c = a % c := by
+  rw (config := {occs := .pos [2]}) [← mod_add_div a b]
+  have ⟨x, h⟩ := h
+  subst h
+  rw [Nat.mul_assoc, add_mul_mod_self_left]
+
+protected theorem dvd_of_mul_dvd_mul_left
+    (kpos : 0 < k) (H : k * m ∣ k * n) : m ∣ n := by
+  let ⟨l, H⟩ := H
+  rw [Nat.mul_assoc] at H
+  exact ⟨_, Nat.eq_of_mul_eq_mul_left kpos H⟩
+
+protected theorem dvd_of_mul_dvd_mul_right (kpos : 0 < k) (H : m * k ∣ n * k) : m ∣ n := by
+  rw [Nat.mul_comm m k, Nat.mul_comm n k] at H; exact Nat.dvd_of_mul_dvd_mul_left kpos H
+
+theorem dvd_sub {k m n : Nat} (H : n ≤ m) (h₁ : k ∣ m) (h₂ : k ∣ n) : k ∣ m - n :=
+  (Nat.dvd_add_iff_left h₂).2 <| by rwa [Nat.sub_add_cancel H]
+
+protected theorem mul_dvd_mul {a b c d : Nat} : a ∣ b → c ∣ d → a * c ∣ b * d
+  | ⟨e, he⟩, ⟨f, hf⟩ =>
+    ⟨e * f, by simp [he, hf, Nat.mul_assoc, Nat.mul_left_comm, Nat.mul_comm]⟩
+
+protected theorem mul_dvd_mul_left (a : Nat) (h : b ∣ c) : a * b ∣ a * c :=
+  Nat.mul_dvd_mul (Nat.dvd_refl a) h
+
+protected theorem mul_dvd_mul_right (h: a ∣ b) (c : Nat) : a * c ∣ b * c :=
+  Nat.mul_dvd_mul h (Nat.dvd_refl c)
+
+@[simp] theorem dvd_one {n : Nat} : n ∣ 1 ↔ n = 1 :=
+  ⟨eq_one_of_dvd_one, fun h => h.symm ▸ Nat.dvd_refl _⟩
+
+protected theorem mul_div_assoc (m : Nat) (H : k ∣ n) : m * n / k = m * (n / k) := by
+  match Nat.eq_zero_or_pos k with
+  | .inl h0 => rw [h0, Nat.div_zero, Nat.div_zero, Nat.mul_zero]
+  | .inr hpos =>
+    have h1 : m * n / k = m * (n / k * k) / k := by rw [Nat.div_mul_cancel H]
+    rw [h1, ← Nat.mul_assoc, Nat.mul_div_cancel _ hpos]
+
+end Nat

src/Init/Data/Nat/Gcd.lean

@@ -1,21 +1,41 @@
 /-
 Copyright (c) 2021 Microsoft Corporation. All rights reserved.
 Released under Apache 2.0 license as described in the file LICENSE.
-Authors: Leonardo de Moura
+Authors: Jeremy Avigad, Leonardo de Moura, Mario Carneiro
 -/
 prelude
-import Init.Data.Nat.Div
+import Init.Data.Nat.Dvd
+import Init.NotationExtra
+import Init.RCases
 
 namespace Nat
 
+/--
+Computes the greatest common divisor of two natural numbers.
+
+This reference implementation via the Euclidean algorithm
+is overridden in both the kernel and the compiler to efficiently
+evaluate using the "bignum" representation (see `Nat`).
+The definition provided here is the logical model
+(and it is soundness-critical that they coincide).
+
+The GCD of two natural numbers is the largest natural number
+that divides both arguments.
+In particular, the GCD of a number and `0` is the number itself:
+```
+example : Nat.gcd 10 15 = 5 := rfl
+example : Nat.gcd 0 5 = 5 := rfl
+example : Nat.gcd 7 0 = 7 := rfl
+```
+-/
 @[extern "lean_nat_gcd"]
 def gcd (m n : @& Nat) : Nat :=
   if m = 0 then
     n
   else
     gcd (n % m) m
-termination_by m
-decreasing_by simp_wf; apply mod_lt _ (zero_lt_of_ne_zero _); assumption
+  termination_by m
+  decreasing_by simp_wf; apply mod_lt _ (zero_lt_of_ne_zero _); assumption
 
 @[simp] theorem gcd_zero_left (y : Nat) : gcd 0 y = y :=
   rfl
@@ -38,4 +58,197 @@ theorem gcd_succ (x y : Nat) : gcd (succ x) y = gcd (y % succ x) (succ x) :=
 @[simp] theorem gcd_self (n : Nat) : gcd n n = n := by
   cases n <;> simp [gcd_succ]
 
+theorem gcd_rec (m n : Nat) : gcd m n = gcd (n % m) m :=
+  match m with
+  | 0 => by have := (mod_zero n).symm; rwa [gcd_zero_right]
+  | _ + 1 => by simp [gcd_succ]
+
+@[elab_as_elim] theorem gcd.induction {P : Nat → Nat → Prop} (m n : Nat)
+    (H0 : ∀n, P 0 n) (H1 : ∀ m n, 0 < m → P (n % m) m → P m n) : P m n :=
+  Nat.strongInductionOn (motive := fun m => ∀ n, P m n) m
+    (fun
+    | 0, _ => H0
+    | _+1, IH => fun _ => H1 _ _ (succ_pos _) (IH _ (mod_lt _ (succ_pos _)) _) )
+    n
+
+theorem gcd_dvd (m n : Nat) : (gcd m n ∣ m) ∧ (gcd m n ∣ n) := by
+  induction m, n using gcd.induction with
+  | H0 n => rw [gcd_zero_left]; exact ⟨Nat.dvd_zero n, Nat.dvd_refl n⟩
+  | H1 m n _ IH => rw [← gcd_rec] at IH; exact ⟨IH.2, (dvd_mod_iff IH.2).1 IH.1⟩
+
+theorem gcd_dvd_left (m n : Nat) : gcd m n ∣ m := (gcd_dvd m n).left
+
+theorem gcd_dvd_right (m n : Nat) : gcd m n ∣ n := (gcd_dvd m n).right
+
+theorem gcd_le_left (n) (h : 0 < m) : gcd m n ≤ m := le_of_dvd h <| gcd_dvd_left m n
+
+theorem gcd_le_right (n) (h : 0 < n) : gcd m n ≤ n := le_of_dvd h <| gcd_dvd_right m n
+
+theorem dvd_gcd : k ∣ m → k ∣ n → k ∣ gcd m n := by
+  induction m, n using gcd.induction with intro km kn
+  | H0 n => rw [gcd_zero_left]; exact kn
+  | H1 n m _ IH => rw [gcd_rec]; exact IH ((dvd_mod_iff km).2 kn) km
+
+theorem dvd_gcd_iff : k ∣ gcd m n ↔ k ∣ m ∧ k ∣ n :=
+  ⟨fun h => let ⟨h₁, h₂⟩ := gcd_dvd m n; ⟨Nat.dvd_trans h h₁, Nat.dvd_trans h h₂⟩,
+   fun ⟨h₁, h₂⟩ => dvd_gcd h₁ h₂⟩
+
+theorem gcd_comm (m n : Nat) : gcd m n = gcd n m :=
+  Nat.dvd_antisymm
+    (dvd_gcd (gcd_dvd_right m n) (gcd_dvd_left m n))
+    (dvd_gcd (gcd_dvd_right n m) (gcd_dvd_left n m))
+
+theorem gcd_eq_left_iff_dvd : m ∣ n ↔ gcd m n = m :=
+  ⟨fun h => by rw [gcd_rec, mod_eq_zero_of_dvd h, gcd_zero_left],
+   fun h => h ▸ gcd_dvd_right m n⟩
+
+theorem gcd_eq_right_iff_dvd : m ∣ n ↔ gcd n m = m := by
+  rw [gcd_comm]; exact gcd_eq_left_iff_dvd
+
+theorem gcd_assoc (m n k : Nat) : gcd (gcd m n) k = gcd m (gcd n k) :=
+  Nat.dvd_antisymm
+    (dvd_gcd
+      (Nat.dvd_trans (gcd_dvd_left (gcd m n) k) (gcd_dvd_left m n))
+      (dvd_gcd (Nat.dvd_trans (gcd_dvd_left (gcd m n) k) (gcd_dvd_right m n))
+        (gcd_dvd_right (gcd m n) k)))
+    (dvd_gcd
+      (dvd_gcd (gcd_dvd_left m (gcd n k))
+        (Nat.dvd_trans (gcd_dvd_right m (gcd n k)) (gcd_dvd_left n k)))
+      (Nat.dvd_trans (gcd_dvd_right m (gcd n k)) (gcd_dvd_right n k)))
+
+@[simp] theorem gcd_one_right (n : Nat) : gcd n 1 = 1 := (gcd_comm n 1).trans (gcd_one_left n)
+
+theorem gcd_mul_left (m n k : Nat) : gcd (m * n) (m * k) = m * gcd n k := by
+  induction n, k using gcd.induction with
+  | H0 k => simp
+  | H1 n k _ IH => rwa [← mul_mod_mul_left, ← gcd_rec, ← gcd_rec] at IH
+
+theorem gcd_mul_right (m n k : Nat) : gcd (m * n) (k * n) = gcd m k * n := by
+  rw [Nat.mul_comm m n, Nat.mul_comm k n, Nat.mul_comm (gcd m k) n, gcd_mul_left]
+
+theorem gcd_pos_of_pos_left {m : Nat} (n : Nat) (mpos : 0 < m) : 0 < gcd m n :=
+  pos_of_dvd_of_pos (gcd_dvd_left m n) mpos
+
+theorem gcd_pos_of_pos_right (m : Nat) {n : Nat} (npos : 0 < n) : 0 < gcd m n :=
+  pos_of_dvd_of_pos (gcd_dvd_right m n) npos
+
+theorem div_gcd_pos_of_pos_left (b : Nat) (h : 0 < a) : 0 < a / a.gcd b :=
+  (Nat.le_div_iff_mul_le <| Nat.gcd_pos_of_pos_left _ h).2 (Nat.one_mul _ ▸ Nat.gcd_le_left _ h)
+
+theorem div_gcd_pos_of_pos_right (a : Nat) (h : 0 < b) : 0 < b / a.gcd b :=
+  (Nat.le_div_iff_mul_le <| Nat.gcd_pos_of_pos_right _ h).2 (Nat.one_mul _ ▸ Nat.gcd_le_right _ h)
+
+theorem eq_zero_of_gcd_eq_zero_left {m n : Nat} (H : gcd m n = 0) : m = 0 :=
+  match eq_zero_or_pos m with
+  | .inl H0 => H0
+  | .inr H1 => absurd (Eq.symm H) (ne_of_lt (gcd_pos_of_pos_left _ H1))
+
+theorem eq_zero_of_gcd_eq_zero_right {m n : Nat} (H : gcd m n = 0) : n = 0 := by
+  rw [gcd_comm] at H
+  exact eq_zero_of_gcd_eq_zero_left H
+
+theorem gcd_ne_zero_left : m ≠ 0 → gcd m n ≠ 0 := mt eq_zero_of_gcd_eq_zero_left
+
+theorem gcd_ne_zero_right : n ≠ 0 → gcd m n ≠ 0 := mt eq_zero_of_gcd_eq_zero_right
+
+theorem gcd_div {m n k : Nat} (H1 : k ∣ m) (H2 : k ∣ n) :
+    gcd (m / k) (n / k) = gcd m n / k :=
+  match eq_zero_or_pos k with
+  | .inl H0 => by simp [H0]
+  | .inr H3 => by
+    apply Nat.eq_of_mul_eq_mul_right H3
+    rw [Nat.div_mul_cancel (dvd_gcd H1 H2), ← gcd_mul_right,
+        Nat.div_mul_cancel H1, Nat.div_mul_cancel H2]
+
+theorem gcd_dvd_gcd_of_dvd_left {m k : Nat} (n : Nat) (H : m ∣ k) : gcd m n ∣ gcd k n :=
+  dvd_gcd (Nat.dvd_trans (gcd_dvd_left m n) H) (gcd_dvd_right m n)
+
+theorem gcd_dvd_gcd_of_dvd_right {m k : Nat} (n : Nat) (H : m ∣ k) : gcd n m ∣ gcd n k :=
+  dvd_gcd (gcd_dvd_left n m) (Nat.dvd_trans (gcd_dvd_right n m) H)
+
+theorem gcd_dvd_gcd_mul_left (m n k : Nat) : gcd m n ∣ gcd (k * m) n :=
+  gcd_dvd_gcd_of_dvd_left _ (Nat.dvd_mul_left _ _)
+
+theorem gcd_dvd_gcd_mul_right (m n k : Nat) : gcd m n ∣ gcd (m * k) n :=
+  gcd_dvd_gcd_of_dvd_left _ (Nat.dvd_mul_right _ _)
+
+theorem gcd_dvd_gcd_mul_left_right (m n k : Nat) : gcd m n ∣ gcd m (k * n) :=
+  gcd_dvd_gcd_of_dvd_right _ (Nat.dvd_mul_left _ _)
+
+theorem gcd_dvd_gcd_mul_right_right (m n k : Nat) : gcd m n ∣ gcd m (n * k) :=
+  gcd_dvd_gcd_of_dvd_right _ (Nat.dvd_mul_right _ _)
+
+theorem gcd_eq_left {m n : Nat} (H : m ∣ n) : gcd m n = m :=
+  Nat.dvd_antisymm (gcd_dvd_left _ _) (dvd_gcd (Nat.dvd_refl _) H)
+
+theorem gcd_eq_right {m n : Nat} (H : n ∣ m) : gcd m n = n := by
+  rw [gcd_comm, gcd_eq_left H]
+
+@[simp] theorem gcd_mul_left_left (m n : Nat) : gcd (m * n) n = n :=
+  Nat.dvd_antisymm (gcd_dvd_right _ _) (dvd_gcd (Nat.dvd_mul_left _ _) (Nat.dvd_refl _))
+
+@[simp] theorem gcd_mul_left_right (m n : Nat) : gcd n (m * n) = n := by
+  rw [gcd_comm, gcd_mul_left_left]
+
+@[simp] theorem gcd_mul_right_left (m n : Nat) : gcd (n * m) n = n := by
+  rw [Nat.mul_comm, gcd_mul_left_left]
+
+@[simp] theorem gcd_mul_right_right (m n : Nat) : gcd n (n * m) = n := by
+  rw [gcd_comm, gcd_mul_right_left]
+
+@[simp] theorem gcd_gcd_self_right_left (m n : Nat) : gcd m (gcd m n) = gcd m n :=
+  Nat.dvd_antisymm (gcd_dvd_right _ _) (dvd_gcd (gcd_dvd_left _ _) (Nat.dvd_refl _))
+
+@[simp] theorem gcd_gcd_self_right_right (m n : Nat) : gcd m (gcd n m) = gcd n m := by
+  rw [gcd_comm n m, gcd_gcd_self_right_left]
+
+@[simp] theorem gcd_gcd_self_left_right (m n : Nat) : gcd (gcd n m) m = gcd n m := by
+  rw [gcd_comm, gcd_gcd_self_right_right]
+
+@[simp] theorem gcd_gcd_self_left_left (m n : Nat) : gcd (gcd m n) m = gcd m n := by
+  rw [gcd_comm m n, gcd_gcd_self_left_right]
+
+theorem gcd_add_mul_self (m n k : Nat) : gcd m (n + k * m) = gcd m n := by
+  simp [gcd_rec m (n + k * m), gcd_rec m n]
+
+theorem gcd_eq_zero_iff {i j : Nat} : gcd i j = 0 ↔ i = 0 ∧ j = 0 :=
+  ⟨fun h => ⟨eq_zero_of_gcd_eq_zero_left h, eq_zero_of_gcd_eq_zero_right h⟩,
+   fun h => by simp [h]⟩
+
+/-- Characterization of the value of `Nat.gcd`. -/
+theorem gcd_eq_iff (a b : Nat) :
+    gcd a b = g ↔ g ∣ a ∧ g ∣ b ∧ (∀ c, c ∣ a → c ∣ b → c ∣ g) := by
+  constructor
+  · rintro rfl
+    exact ⟨gcd_dvd_left _ _, gcd_dvd_right _ _, fun _ => Nat.dvd_gcd⟩
+  · rintro ⟨ha, hb, hc⟩
+    apply Nat.dvd_antisymm
+    · apply hc
+      · exact gcd_dvd_left a b
+      · exact gcd_dvd_right a b
+    · exact Nat.dvd_gcd ha hb
+
+/-- Represent a divisor of `m * n` as a product of a divisor of `m` and a divisor of `n`. -/
+def prod_dvd_and_dvd_of_dvd_prod {k m n : Nat} (H : k ∣ m * n) :
+    {d : {m' // m' ∣ m} × {n' // n' ∣ n} // k = d.1.val * d.2.val} :=
+  if h0 : gcd k m = 0 then
+    ⟨⟨⟨0, eq_zero_of_gcd_eq_zero_right h0 ▸ Nat.dvd_refl 0⟩,
+      ⟨n, Nat.dvd_refl n⟩⟩,
+      eq_zero_of_gcd_eq_zero_left h0 ▸ (Nat.zero_mul n).symm⟩
+  else by
+    have hd : gcd k m * (k / gcd k m) = k := Nat.mul_div_cancel' (gcd_dvd_left k m)
+    refine ⟨⟨⟨gcd k m, gcd_dvd_right k m⟩, ⟨k / gcd k m, ?_⟩⟩, hd.symm⟩
+    apply Nat.dvd_of_mul_dvd_mul_left (Nat.pos_of_ne_zero h0)
+    rw [hd, ← gcd_mul_right]
+    exact Nat.dvd_gcd (Nat.dvd_mul_right _ _) H
+
+theorem gcd_mul_dvd_mul_gcd (k m n : Nat) : gcd k (m * n) ∣ gcd k m * gcd k n := by
+  let ⟨⟨⟨m', hm'⟩, ⟨n', hn'⟩⟩, (h : gcd k (m * n) = m' * n')⟩ :=
+    prod_dvd_and_dvd_of_dvd_prod <| gcd_dvd_right k (m * n)
+  rw [h]
+  have h' : m' * n' ∣ k := h ▸ gcd_dvd_left ..
+  exact Nat.mul_dvd_mul
+    (dvd_gcd (Nat.dvd_trans (Nat.dvd_mul_right m' n') h') hm')
+    (dvd_gcd (Nat.dvd_trans (Nat.dvd_mul_left n' m') h') hn')
+
 end Nat

src/Init/Data/Nat/Lcm.lean

@@ -0,0 +1,66 @@
+/-
+Copyright (c) 2014 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Jeremy Avigad, Leonardo de Moura, Mario Carneiro
+-/
+prelude
+import Init.Data.Nat.Gcd
+import Init.Data.Nat.Lemmas
+
+namespace Nat
+
+/-- The least common multiple of `m` and `n`, defined using `gcd`. -/
+def lcm (m n : Nat) : Nat := m * n / gcd m n
+
+theorem lcm_comm (m n : Nat) : lcm m n = lcm n m := by
+  rw [lcm, lcm, Nat.mul_comm n m, gcd_comm n m]
+
+@[simp] theorem lcm_zero_left (m : Nat) : lcm 0 m = 0 := by simp [lcm]
+
+@[simp] theorem lcm_zero_right (m : Nat) : lcm m 0 = 0 := by simp [lcm]
+
+@[simp] theorem lcm_one_left (m : Nat) : lcm 1 m = m := by simp [lcm]
+
+@[simp] theorem lcm_one_right (m : Nat) : lcm m 1 = m := by simp [lcm]
+
+@[simp] theorem lcm_self (m : Nat) : lcm m m = m := by
+  match eq_zero_or_pos m with
+  | .inl h => rw [h, lcm_zero_left]
+  | .inr h => simp [lcm, Nat.mul_div_cancel _ h]
+
+theorem dvd_lcm_left (m n : Nat) : m ∣ lcm m n :=
+  ⟨n / gcd m n, by rw [← Nat.mul_div_assoc m (Nat.gcd_dvd_right m n)]; rfl⟩
+
+theorem dvd_lcm_right (m n : Nat) : n ∣ lcm m n := lcm_comm n m ▸ dvd_lcm_left n m
+
+theorem gcd_mul_lcm (m n : Nat) : gcd m n * lcm m n = m * n := by
+  rw [lcm, Nat.mul_div_cancel' (Nat.dvd_trans (gcd_dvd_left m n) (Nat.dvd_mul_right m n))]
+
+theorem lcm_dvd {m n k : Nat} (H1 : m ∣ k) (H2 : n ∣ k) : lcm m n ∣ k := by
+  match eq_zero_or_pos k with
+  | .inl h => rw [h]; exact Nat.dvd_zero _
+  | .inr kpos =>
+    apply Nat.dvd_of_mul_dvd_mul_left (gcd_pos_of_pos_left n (pos_of_dvd_of_pos H1 kpos))
+    rw [gcd_mul_lcm, ← gcd_mul_right, Nat.mul_comm n k]
+    exact dvd_gcd (Nat.mul_dvd_mul_left _ H2) (Nat.mul_dvd_mul_right H1 _)
+
+theorem lcm_assoc (m n k : Nat) : lcm (lcm m n) k = lcm m (lcm n k) :=
+Nat.dvd_antisymm
+  (lcm_dvd
+    (lcm_dvd (dvd_lcm_left m (lcm n k))
+      (Nat.dvd_trans (dvd_lcm_left n k) (dvd_lcm_right m (lcm n k))))
+    (Nat.dvd_trans (dvd_lcm_right n k) (dvd_lcm_right m (lcm n k))))
+  (lcm_dvd
+    (Nat.dvd_trans (dvd_lcm_left m n) (dvd_lcm_left (lcm m n) k))
+    (lcm_dvd (Nat.dvd_trans (dvd_lcm_right m n) (dvd_lcm_left (lcm m n) k))
+      (dvd_lcm_right (lcm m n) k)))
+
+theorem lcm_ne_zero (hm : m ≠ 0) (hn : n ≠ 0) : lcm m n ≠ 0 := by
+  intro h
+  have h1 := gcd_mul_lcm m n
+  rw [h, Nat.mul_zero] at h1
+  match mul_eq_zero.1 h1.symm with
+  | .inl hm1 => exact hm hm1
+  | .inr hn1 => exact hn hn1
+
+end Nat

src/Init/Data/Nat/Lemmas.lean

@@ -0,0 +1,832 @@
+/-
+Copyright (c) 2016 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Leonardo de Moura, Jeremy Avigad, Mario Carneiro
+-/
+prelude
+import Init.Data.Nat.MinMax
+import Init.Data.Nat.Log2
+import Init.Data.Nat.Power2
+import Init.Omega
+
+/-! # Basic lemmas about natural numbers
+
+The primary purpose of the lemmas in this file is to assist with reasoning
+about sizes of objects, array indices and such.
+
+This file was upstreamed from Std,
+and later these lemmas should be organised into other files more systematically.
+-/
+
+namespace Nat
+/-! ## add -/
+
+protected theorem add_add_add_comm (a b c d : Nat) : (a + b) + (c + d) = (a + c) + (b + d) := by
+  rw [Nat.add_assoc, Nat.add_assoc, Nat.add_left_comm b]
+
+theorem one_add (n) : 1 + n = succ n := Nat.add_comm ..
+
+theorem succ_eq_one_add (n) : succ n = 1 + n := (one_add _).symm
+
+theorem succ_add_eq_add_succ (a b) : succ a + b = a + succ b := Nat.succ_add ..
+
+protected theorem eq_zero_of_add_eq_zero_right (h : n + m = 0) : n = 0 :=
+  (Nat.eq_zero_of_add_eq_zero h).1
+
+protected theorem add_eq_zero_iff : n + m = 0 ↔ n = 0 ∧ m = 0 :=
+  ⟨Nat.eq_zero_of_add_eq_zero, fun ⟨h₁, h₂⟩ => h₂.symm ▸ h₁⟩
+
+protected theorem add_left_cancel_iff {n : Nat} : n + m = n + k ↔ m = k :=
+  ⟨Nat.add_left_cancel, fun | rfl => rfl⟩
+
+protected theorem add_right_cancel_iff {n : Nat} : m + n = k + n ↔ m = k :=
+  ⟨Nat.add_right_cancel, fun | rfl => rfl⟩
+
+protected theorem add_le_add_iff_left {n : Nat} : n + m ≤ n + k ↔ m ≤ k :=
+  ⟨Nat.le_of_add_le_add_left, fun h => Nat.add_le_add_left h _⟩
+
+protected theorem lt_of_add_lt_add_right : ∀ {n : Nat}, k + n < m + n → k < m
+  | 0, h => h
+  | _+1, h => Nat.lt_of_add_lt_add_right (Nat.lt_of_succ_lt_succ h)
+
+protected theorem lt_of_add_lt_add_left {n : Nat} : n + k < n + m → k < m := by
+  rw [Nat.add_comm n, Nat.add_comm n]; exact Nat.lt_of_add_lt_add_right
+
+protected theorem add_lt_add_iff_left {k n m : Nat} : k + n < k + m ↔ n < m :=
+  ⟨Nat.lt_of_add_lt_add_left, fun h => Nat.add_lt_add_left h _⟩
+
+protected theorem add_lt_add_iff_right {k n m : Nat} : n + k < m + k ↔ n < m :=
+  ⟨Nat.lt_of_add_lt_add_right, fun h => Nat.add_lt_add_right h _⟩
+
+protected theorem add_lt_add_of_le_of_lt {a b c d : Nat} (hle : a ≤ b) (hlt : c < d) :
+    a + c < b + d :=
+  Nat.lt_of_le_of_lt (Nat.add_le_add_right hle _) (Nat.add_lt_add_left hlt _)
+
+protected theorem add_lt_add_of_lt_of_le {a b c d : Nat} (hlt : a < b) (hle : c ≤ d) :
+    a + c < b + d :=
+  Nat.lt_of_le_of_lt (Nat.add_le_add_left hle _) (Nat.add_lt_add_right hlt _)
+
+protected theorem lt_add_of_pos_left : 0 < k → n < k + n := by
+  rw [Nat.add_comm]; exact Nat.lt_add_of_pos_right
+
+protected theorem pos_of_lt_add_right (h : n < n + k) : 0 < k :=
+  Nat.lt_of_add_lt_add_left h
+
+protected theorem pos_of_lt_add_left : n < k + n → 0 < k := by
+  rw [Nat.add_comm]; exact Nat.pos_of_lt_add_right
+
+protected theorem lt_add_right_iff_pos : n < n + k ↔ 0 < k :=
+  ⟨Nat.pos_of_lt_add_right, Nat.lt_add_of_pos_right⟩
+
+protected theorem lt_add_left_iff_pos : n < k + n ↔ 0 < k :=
+  ⟨Nat.pos_of_lt_add_left, Nat.lt_add_of_pos_left⟩
+
+protected theorem add_pos_left (h : 0 < m) (n) : 0 < m + n :=
+  Nat.lt_of_lt_of_le h (Nat.le_add_right ..)
+
+protected theorem add_pos_right (m) (h : 0 < n) : 0 < m + n :=
+  Nat.lt_of_lt_of_le h (Nat.le_add_left ..)
+
+protected theorem add_self_ne_one : ∀ n, n + n ≠ 1
+  | n+1, h => by rw [Nat.succ_add, Nat.succ.injEq] at h; contradiction
+
+/-! ## sub -/
+
+protected theorem sub_one (n) : n - 1 = pred n := rfl
+
+protected theorem one_sub : ∀ n, 1 - n = if n = 0 then 1 else 0
+  | 0 => rfl
+  | _+1 => by rw [if_neg (Nat.succ_ne_zero _), Nat.succ_sub_succ, Nat.zero_sub]
+
+theorem succ_sub_sub_succ (n m k) : succ n - m - succ k = n - m - k := by
+  rw [Nat.sub_sub, Nat.sub_sub, add_succ, succ_sub_succ]
+
+protected theorem sub_right_comm (m n k : Nat) : m - n - k = m - k - n := by
+  rw [Nat.sub_sub, Nat.sub_sub, Nat.add_comm]
+
+protected theorem add_sub_cancel_right (n m : Nat) : (n + m) - m = n := Nat.add_sub_cancel ..
+
+@[simp] protected theorem add_sub_cancel' {n m : Nat} (h : m ≤ n) : m + (n - m) = n := by
+  rw [Nat.add_comm, Nat.sub_add_cancel h]
+
+theorem succ_sub_one (n) : succ n - 1 = n := rfl
+
+protected theorem add_one_sub_one (n : Nat) : (n + 1) - 1 = n := rfl
+
+protected theorem one_add_sub_one (n : Nat) : (1 + n) - 1 = n := Nat.add_sub_cancel_left 1 _
+
+protected theorem sub_sub_self {n m : Nat} (h : m ≤ n) : n - (n - m) = m :=
+  (Nat.sub_eq_iff_eq_add (Nat.sub_le ..)).2 (Nat.add_sub_of_le h).symm
+
+protected theorem sub_add_comm {n m k : Nat} (h : k ≤ n) : n + m - k = n - k + m := by
+  rw [Nat.sub_eq_iff_eq_add (Nat.le_trans h (Nat.le_add_right ..))]
+  rwa [Nat.add_right_comm, Nat.sub_add_cancel]
+
+protected theorem sub_eq_zero_iff_le : n - m = 0 ↔ n ≤ m :=
+  ⟨Nat.le_of_sub_eq_zero, Nat.sub_eq_zero_of_le⟩
+
+protected theorem sub_pos_iff_lt : 0 < n - m ↔ m < n :=
+  ⟨Nat.lt_of_sub_pos, Nat.sub_pos_of_lt⟩
+
+protected theorem sub_le_iff_le_add {a b c : Nat} : a - b ≤ c ↔ a ≤ c + b :=
+  ⟨Nat.le_add_of_sub_le, sub_le_of_le_add⟩
+
+protected theorem sub_le_iff_le_add' {a b c : Nat} : a - b ≤ c ↔ a ≤ b + c := by
+  rw [Nat.add_comm, Nat.sub_le_iff_le_add]
+
+protected theorem le_sub_iff_add_le {n : Nat} (h : k ≤ m) : n ≤ m - k ↔ n + k ≤ m :=
+  ⟨Nat.add_le_of_le_sub h, Nat.le_sub_of_add_le⟩
+
+@[deprecated Nat.le_sub_iff_add_le]
+protected theorem add_le_to_le_sub (n : Nat) (h : m ≤ k) : n + m ≤ k ↔ n ≤ k - m :=
+  (Nat.le_sub_iff_add_le h).symm
+
+protected theorem add_le_of_le_sub' {n k m : Nat} (h : m ≤ k) : n ≤ k - m → m + n ≤ k :=
+  Nat.add_comm .. ▸ Nat.add_le_of_le_sub h
+
+@[deprecated Nat.add_le_of_le_sub']
+protected theorem add_le_of_le_sub_left {n k m : Nat} (h : m ≤ k) : n ≤ k - m → m + n ≤ k :=
+  Nat.add_le_of_le_sub' h
+
+protected theorem le_sub_of_add_le' {n k m : Nat} : m + n ≤ k → n ≤ k - m :=
+  Nat.add_comm .. ▸ Nat.le_sub_of_add_le
+
+protected theorem le_sub_iff_add_le' {n : Nat} (h : k ≤ m) : n ≤ m - k ↔ k + n ≤ m :=
+  ⟨Nat.add_le_of_le_sub' h, Nat.le_sub_of_add_le'⟩
+
+protected theorem le_of_sub_le_sub_left : ∀ {n k m : Nat}, n ≤ k → k - m ≤ k - n → n ≤ m
+  | 0, _, _, _, _ => Nat.zero_le ..
+  | _+1, _, 0, h₀, h₁ =>
+    absurd (Nat.sub_lt (Nat.zero_lt_of_lt h₀) (Nat.zero_lt_succ _)) (Nat.not_lt.2 h₁)
+  | _+1, _+1, _+1, h₀, h₁ => by
+    simp only [Nat.succ_sub_succ] at h₁
+    exact succ_le_succ <| Nat.le_of_sub_le_sub_left (Nat.le_of_succ_le_succ h₀) h₁
+
+protected theorem sub_le_sub_iff_left {n m k : Nat} (h : n ≤ k) : k - m ≤ k - n ↔ n ≤ m :=
+  ⟨Nat.le_of_sub_le_sub_left h, fun h => Nat.sub_le_sub_left h _⟩
+
+protected theorem sub_lt_of_pos_le (h₀ : 0 < a) (h₁ : a ≤ b) : b - a < b :=
+  Nat.sub_lt (Nat.lt_of_lt_of_le h₀ h₁) h₀
+protected abbrev sub_lt_self := @Nat.sub_lt_of_pos_le
+
+theorem add_lt_of_lt_sub' {a b c : Nat} : b < c - a → a + b < c := by
+  rw [Nat.add_comm]; exact Nat.add_lt_of_lt_sub
+
+protected theorem sub_add_lt_sub (h₁ : m + k ≤ n) (h₂ : 0 < k) : n - (m + k) < n - m := by
+  rw [← Nat.sub_sub]; exact Nat.sub_lt_of_pos_le h₂ (Nat.le_sub_of_add_le' h₁)
+
+theorem sub_one_lt_of_le (h₀ : 0 < a) (h₁ : a ≤ b) : a - 1 < b :=
+  Nat.lt_of_lt_of_le (Nat.pred_lt' h₀) h₁
+
+theorem sub_lt_succ (a b) : a - b < succ a := lt_succ_of_le (sub_le a b)
+
+theorem sub_one_sub_lt (h : i < n) : n - 1 - i < n := by
+  rw [Nat.sub_right_comm]; exact Nat.sub_one_lt_of_le (Nat.sub_pos_of_lt h) (Nat.sub_le ..)
+
+protected theorem exists_eq_add_of_le (h : m ≤ n) : ∃ k : Nat, n = m + k :=
+  ⟨n - m, (add_sub_of_le h).symm⟩
+
+protected theorem exists_eq_add_of_le' (h : m ≤ n) : ∃ k : Nat, n = k + m :=
+  ⟨n - m, (Nat.sub_add_cancel h).symm⟩
+
+protected theorem exists_eq_add_of_lt (h : m < n) : ∃ k : Nat, n = m + k + 1 :=
+  ⟨n - (m + 1), by rw [Nat.add_right_comm, add_sub_of_le h]⟩
+
+/-! ### min/max -/
+
+theorem succ_min_succ (x y) : min (succ x) (succ y) = succ (min x y) := by
+  cases Nat.le_total x y with
+  | inl h => rw [Nat.min_eq_left h, Nat.min_eq_left (Nat.succ_le_succ h)]
+  | inr h => rw [Nat.min_eq_right h, Nat.min_eq_right (Nat.succ_le_succ h)]
+
+@[simp] protected theorem min_self (a : Nat) : min a a = a := Nat.min_eq_left (Nat.le_refl _)
+
+@[simp] protected theorem zero_min (a) : min 0 a = 0 := Nat.min_eq_left (Nat.zero_le _)
+
+@[simp] protected theorem min_zero (a) : min a 0 = 0 := Nat.min_eq_right (Nat.zero_le _)
+
+protected theorem min_assoc : ∀ (a b c : Nat), min (min a b) c = min a (min b c)
+  | 0, _, _ => by rw [Nat.zero_min, Nat.zero_min, Nat.zero_min]
+  | _, 0, _ => by rw [Nat.zero_min, Nat.min_zero, Nat.zero_min]
+  | _, _, 0 => by rw [Nat.min_zero, Nat.min_zero, Nat.min_zero]
+  | _+1, _+1, _+1 => by simp only [Nat.succ_min_succ]; exact congrArg succ <| Nat.min_assoc ..
+
+protected theorem sub_sub_eq_min : ∀ (a b : Nat), a - (a - b) = min a b
+  | 0, _ => by rw [Nat.zero_sub, Nat.zero_min]
+  | _, 0 => by rw [Nat.sub_zero, Nat.sub_self, Nat.min_zero]
+  | _+1, _+1 => by
+    rw [Nat.succ_sub_succ, Nat.succ_min_succ, Nat.succ_sub (Nat.sub_le ..)]
+    exact congrArg succ <| Nat.sub_sub_eq_min ..
+
+protected theorem sub_eq_sub_min (n m : Nat) : n - m = n - min n m := by
+  cases Nat.le_total n m with
+  | inl h => rw [Nat.min_eq_left h, Nat.sub_eq_zero_of_le h, Nat.sub_self]
+  | inr h => rw [Nat.min_eq_right h]
+
+@[simp] protected theorem sub_add_min_cancel (n m : Nat) : n - m + min n m = n := by
+  rw [Nat.sub_eq_sub_min, Nat.sub_add_cancel (Nat.min_le_left ..)]
+
+protected theorem max_eq_right {a b : Nat} (h : a ≤ b) : max a b = b := if_pos h
+
+protected theorem max_eq_left {a b : Nat} (h : b ≤ a) : max a b = a := by
+  rw [Nat.max_comm]; exact Nat.max_eq_right h
+
+protected theorem succ_max_succ (x y) : max (succ x) (succ y) = succ (max x y) := by
+  cases Nat.le_total x y with
+  | inl h => rw [Nat.max_eq_right h, Nat.max_eq_right (Nat.succ_le_succ h)]
+  | inr h => rw [Nat.max_eq_left h, Nat.max_eq_left (Nat.succ_le_succ h)]
+
+protected theorem max_le_of_le_of_le {a b c : Nat} : a ≤ c → b ≤ c → max a b ≤ c := by
+  intros; cases Nat.le_total a b with
+  | inl h => rw [Nat.max_eq_right h]; assumption
+  | inr h => rw [Nat.max_eq_left h]; assumption
+
+protected theorem max_le {a b c : Nat} : max a b ≤ c ↔ a ≤ c ∧ b ≤ c :=
+  ⟨fun h => ⟨Nat.le_trans (Nat.le_max_left ..) h, Nat.le_trans (Nat.le_max_right ..) h⟩,
+   fun ⟨h₁, h₂⟩ => Nat.max_le_of_le_of_le h₁ h₂⟩
+
+protected theorem max_lt {a b c : Nat} : max a b < c ↔ a < c ∧ b < c := by
+  rw [← Nat.succ_le, ← Nat.succ_max_succ a b]; exact Nat.max_le
+
+@[simp] protected theorem max_self (a : Nat) : max a a = a := Nat.max_eq_right (Nat.le_refl _)
+
+@[simp] protected theorem zero_max (a) : max 0 a = a := Nat.max_eq_right (Nat.zero_le _)
+
+@[simp] protected theorem max_zero (a) : max a 0 = a := Nat.max_eq_left (Nat.zero_le _)
+
+protected theorem max_assoc : ∀ (a b c : Nat), max (max a b) c = max a (max b c)
+  | 0, _, _ => by rw [Nat.zero_max, Nat.zero_max]
+  | _, 0, _ => by rw [Nat.zero_max, Nat.max_zero]
+  | _, _, 0 => by rw [Nat.max_zero, Nat.max_zero]
+  | _+1, _+1, _+1 => by simp only [Nat.succ_max_succ]; exact congrArg succ <| Nat.max_assoc ..
+
+protected theorem sub_add_eq_max (a b : Nat) : a - b + b = max a b := by
+  match Nat.le_total a b with
+  | .inl hl => rw [Nat.max_eq_right hl, Nat.sub_eq_zero_iff_le.mpr hl, Nat.zero_add]
+  | .inr hr => rw [Nat.max_eq_left hr, Nat.sub_add_cancel hr]
+
+protected theorem sub_eq_max_sub (n m : Nat) : n - m = max n m - m := by
+  cases Nat.le_total m n with
+  | inl h => rw [Nat.max_eq_left h]
+  | inr h => rw [Nat.max_eq_right h, Nat.sub_eq_zero_of_le h, Nat.sub_self]
+
+protected theorem max_min_distrib_left : ∀ (a b c : Nat), max a (min b c) = min (max a b) (max a c)
+  | 0, _, _ => by simp only [Nat.zero_max]
+  | _, 0, _ => by
+    rw [Nat.zero_min, Nat.max_zero]
+    exact Nat.min_eq_left (Nat.le_max_left ..) |>.symm
+  | _, _, 0 => by
+    rw [Nat.min_zero, Nat.max_zero]
+    exact Nat.min_eq_right (Nat.le_max_left ..) |>.symm
+  | _+1, _+1, _+1 => by
+    simp only [Nat.succ_max_succ, Nat.succ_min_succ]
+    exact congrArg succ <| Nat.max_min_distrib_left ..
+
+protected theorem min_max_distrib_left : ∀ (a b c : Nat), min a (max b c) = max (min a b) (min a c)
+  | 0, _, _ => by simp only [Nat.zero_min, Nat.max_self]
+  | _, 0, _ => by simp only [Nat.min_zero, Nat.zero_max]
+  | _, _, 0 => by simp only [Nat.min_zero, Nat.max_zero]
+  | _+1, _+1, _+1 => by
+    simp only [Nat.succ_max_succ, Nat.succ_min_succ]
+    exact congrArg succ <| Nat.min_max_distrib_left ..
+
+protected theorem max_min_distrib_right (a b c : Nat) :
+    max (min a b) c = min (max a c) (max b c) := by
+  repeat rw [Nat.max_comm _ c]
+  exact Nat.max_min_distrib_left ..
+
+protected theorem min_max_distrib_right (a b c : Nat) :
+    min (max a b) c = max (min a c) (min b c) := by
+  repeat rw [Nat.min_comm _ c]
+  exact Nat.min_max_distrib_left ..
+
+protected theorem add_max_add_right : ∀ (a b c : Nat), max (a + c) (b + c) = max a b + c
+  | _, _, 0 => rfl
+  | _, _, _+1 => Eq.trans (Nat.succ_max_succ ..) <| congrArg _ (Nat.add_max_add_right ..)
+
+protected theorem add_min_add_right : ∀ (a b c : Nat), min (a + c) (b + c) = min a b + c
+  | _, _, 0 => rfl
+  | _, _, _+1 => Eq.trans (Nat.succ_min_succ ..) <| congrArg _ (Nat.add_min_add_right ..)
+
+protected theorem add_max_add_left (a b c : Nat) : max (a + b) (a + c) = a + max b c := by
+  repeat rw [Nat.add_comm a]
+  exact Nat.add_max_add_right ..
+
+protected theorem add_min_add_left (a b c : Nat) : min (a + b) (a + c) = a + min b c := by
+  repeat rw [Nat.add_comm a]
+  exact Nat.add_min_add_right ..
+
+protected theorem pred_min_pred : ∀ (x y), min (pred x) (pred y) = pred (min x y)
+  | 0, _ => by simp only [Nat.pred_zero, Nat.zero_min]
+  | _, 0 => by simp only [Nat.pred_zero, Nat.min_zero]
+  | _+1, _+1 => by simp only [Nat.pred_succ, Nat.succ_min_succ]
+
+protected theorem pred_max_pred : ∀ (x y), max (pred x) (pred y) = pred (max x y)
+  | 0, _ => by simp only [Nat.pred_zero, Nat.zero_max]
+  | _, 0 => by simp only [Nat.pred_zero, Nat.max_zero]
+  | _+1, _+1 => by simp only [Nat.pred_succ, Nat.succ_max_succ]
+
+protected theorem sub_min_sub_right : ∀ (a b c : Nat), min (a - c) (b - c) = min a b - c
+  | _, _, 0 => rfl
+  | _, _, _+1 => Eq.trans (Nat.pred_min_pred ..) <| congrArg _ (Nat.sub_min_sub_right ..)
+
+protected theorem sub_max_sub_right : ∀ (a b c : Nat), max (a - c) (b - c) = max a b - c
+  | _, _, 0 => rfl
+  | _, _, _+1 => Eq.trans (Nat.pred_max_pred ..) <| congrArg _ (Nat.sub_max_sub_right ..)
+
+protected theorem sub_min_sub_left (a b c : Nat) : min (a - b) (a - c) = a - max b c := by
+  omega
+
+protected theorem sub_max_sub_left (a b c : Nat) : max (a - b) (a - c) = a - min b c := by
+  omega
+
+protected theorem mul_max_mul_right (a b c : Nat) : max (a * c) (b * c) = max a b * c := by
+  induction a generalizing b with
+  | zero => simp
+  | succ i ind =>
+    cases b <;> simp [succ_eq_add_one, Nat.succ_mul, Nat.add_max_add_right, ind]
+
+protected theorem mul_min_mul_right (a b c : Nat) : min (a * c) (b * c) = min a b * c := by
+  induction a generalizing b with
+  | zero => simp
+  | succ i ind =>
+    cases b <;> simp [succ_eq_add_one, Nat.succ_mul, Nat.add_min_add_right, ind]
+
+protected theorem mul_max_mul_left (a b c : Nat) : max (a * b) (a * c) = a * max b c := by
+  repeat rw [Nat.mul_comm a]
+  exact Nat.mul_max_mul_right ..
+
+protected theorem mul_min_mul_left (a b c : Nat) : min (a * b) (a * c) = a * min b c := by
+  repeat rw [Nat.mul_comm a]
+  exact Nat.mul_min_mul_right ..
+
+-- protected theorem sub_min_sub_left (a b c : Nat) : min (a - b) (a - c) = a - max b c := by
+--   induction b, c using Nat.recDiagAux with
+--   | zero_left => rw [Nat.sub_zero, Nat.zero_max]; exact Nat.min_eq_right (Nat.sub_le ..)
+--   | zero_right => rw [Nat.sub_zero, Nat.max_zero]; exact Nat.min_eq_left (Nat.sub_le ..)
+--   | succ_succ _ _ ih => simp only [Nat.sub_succ, Nat.succ_max_succ, Nat.pred_min_pred, ih]
+
+-- protected theorem sub_max_sub_left (a b c : Nat) : max (a - b) (a - c) = a - min b c := by
+--   induction b, c using Nat.recDiagAux with
+--   | zero_left => rw [Nat.sub_zero, Nat.zero_min]; exact Nat.max_eq_left (Nat.sub_le ..)
+--   | zero_right => rw [Nat.sub_zero, Nat.min_zero]; exact Nat.max_eq_right (Nat.sub_le ..)
+--   | succ_succ _ _ ih => simp only [Nat.sub_succ, Nat.succ_min_succ, Nat.pred_max_pred, ih]
+
+-- protected theorem mul_max_mul_right (a b c : Nat) : max (a * c) (b * c) = max a b * c := by
+--   induction a, b using Nat.recDiagAux with
+--   | zero_left => simp only [Nat.zero_mul, Nat.zero_max]
+--   | zero_right => simp only [Nat.zero_mul, Nat.max_zero]
+--   | succ_succ _ _ ih => simp only [Nat.succ_mul, Nat.add_max_add_right, ih]
+
+-- protected theorem mul_min_mul_right (a b c : Nat) : min (a * c) (b * c) = min a b * c := by
+--   induction a, b using Nat.recDiagAux with
+--   | zero_left => simp only [Nat.zero_mul, Nat.zero_min]
+--   | zero_right => simp only [Nat.zero_mul, Nat.min_zero]
+--   | succ_succ _ _ ih => simp only [Nat.succ_mul, Nat.add_min_add_right, ih]
+
+-- protected theorem mul_max_mul_left (a b c : Nat) : max (a * b) (a * c) = a * max b c := by
+--   repeat rw [Nat.mul_comm a]
+--   exact Nat.mul_max_mul_right ..
+
+-- protected theorem mul_min_mul_left (a b c : Nat) : min (a * b) (a * c) = a * min b c := by
+--   repeat rw [Nat.mul_comm a]
+--   exact Nat.mul_min_mul_right ..
+
+/-! ### mul -/
+
+@[deprecated Nat.mul_le_mul_left]
+protected theorem mul_le_mul_of_nonneg_left {a b c : Nat} : a ≤ b → c * a ≤ c * b :=
+  Nat.mul_le_mul_left c
+
+@[deprecated Nat.mul_le_mul_right]
+protected theorem mul_le_mul_of_nonneg_right {a b c : Nat} : a ≤ b → a * c ≤ b * c :=
+  Nat.mul_le_mul_right c
+
+protected theorem mul_right_comm (n m k : Nat) : n * m * k = n * k * m := by
+  rw [Nat.mul_assoc, Nat.mul_comm m, ← Nat.mul_assoc]
+
+protected theorem mul_mul_mul_comm (a b c d : Nat) : (a * b) * (c * d) = (a * c) * (b * d) := by
+  rw [Nat.mul_assoc, Nat.mul_assoc, Nat.mul_left_comm b]
+
+theorem mul_eq_zero : ∀ {m n}, n * m = 0 ↔ n = 0 ∨ m = 0
+  | 0, _ => ⟨fun _ => .inr rfl, fun _ => rfl⟩
+  | _, 0 => ⟨fun _ => .inl rfl, fun _ => Nat.zero_mul ..⟩
+  | _+1, _+1 => ⟨nofun, nofun⟩
+
+protected theorem mul_ne_zero_iff : n * m ≠ 0 ↔ n ≠ 0 ∧ m ≠ 0 := by rw [ne_eq, mul_eq_zero, not_or]
+
+protected theorem mul_ne_zero : n ≠ 0 → m ≠ 0 → n * m ≠ 0 := (Nat.mul_ne_zero_iff.2 ⟨·,·⟩)
+
+protected theorem ne_zero_of_mul_ne_zero_left (h : n * m ≠ 0) : n ≠ 0 :=
+  (Nat.mul_ne_zero_iff.1 h).1
+
+protected theorem mul_left_cancel {n m k : Nat} (np : 0 < n) (h : n * m = n * k) : m = k := by
+  match Nat.lt_trichotomy m k with
+  | Or.inl p =>
+    have r : n * m < n * k := Nat.mul_lt_mul_of_pos_left p np
+    simp [h] at r
+  | Or.inr (Or.inl p) => exact p
+  | Or.inr (Or.inr p) =>
+    have r : n * k < n * m := Nat.mul_lt_mul_of_pos_left p np
+    simp [h] at r
+
+protected theorem mul_right_cancel {n m k : Nat} (mp : 0 < m) (h : n * m = k * m) : n = k := by
+  simp [Nat.mul_comm _ m] at h
+  apply Nat.mul_left_cancel mp h
+
+protected theorem mul_left_cancel_iff {n: Nat} (p : 0 < n) (m k : Nat) : n * m = n * k ↔ m = k :=
+  ⟨Nat.mul_left_cancel p, fun | rfl => rfl⟩
+
+protected theorem mul_right_cancel_iff {m : Nat} (p : 0 < m) (n k : Nat) : n * m = k * m ↔ n = k :=
+  ⟨Nat.mul_right_cancel p, fun | rfl => rfl⟩
+
+protected theorem ne_zero_of_mul_ne_zero_right (h : n * m ≠ 0) : m ≠ 0 :=
+  (Nat.mul_ne_zero_iff.1 h).2
+
+protected theorem le_mul_of_pos_left (m) (h : 0 < n) : m ≤ n * m :=
+  Nat.le_trans (Nat.le_of_eq (Nat.one_mul _).symm) (Nat.mul_le_mul_right _ h)
+
+protected theorem le_mul_of_pos_right (n) (h : 0 < m) : n ≤ n * m :=
+  Nat.le_trans (Nat.le_of_eq (Nat.mul_one _).symm) (Nat.mul_le_mul_left _ h)
+
+protected theorem mul_lt_mul_of_lt_of_le (hac : a < c) (hbd : b ≤ d) (hd : 0 < d) :
+    a * b < c * d :=
+  Nat.lt_of_le_of_lt (Nat.mul_le_mul_left _ hbd) (Nat.mul_lt_mul_of_pos_right hac hd)
+
+protected theorem mul_lt_mul_of_lt_of_le' (hac : a < c) (hbd : b ≤ d) (hb : 0 < b) :
+    a * b < c * d :=
+  Nat.mul_lt_mul_of_lt_of_le hac hbd (Nat.lt_of_lt_of_le hb hbd)
+
+protected theorem mul_lt_mul_of_le_of_lt (hac : a ≤ c) (hbd : b < d) (hc : 0 < c) :
+    a * b < c * d :=
+  Nat.lt_of_le_of_lt (Nat.mul_le_mul_right _ hac) (Nat.mul_lt_mul_of_pos_left hbd hc)
+
+protected theorem mul_lt_mul_of_le_of_lt' (hac : a ≤ c) (hbd : b < d) (ha : 0 < a) :
+    a * b < c * d :=
+  Nat.mul_lt_mul_of_le_of_lt hac hbd (Nat.lt_of_lt_of_le ha hac)
+
+protected theorem mul_lt_mul_of_lt_of_lt {a b c d : Nat} (hac : a < c) (hbd : b < d) :
+    a * b < c * d :=
+  Nat.mul_lt_mul_of_le_of_lt (Nat.le_of_lt hac) hbd (Nat.zero_lt_of_lt hac)
+
+theorem succ_mul_succ (a b) : succ a * succ b = a * b + a + b + 1 := by
+  rw [succ_mul, mul_succ]; rfl
+theorem mul_le_add_right (m k n : Nat) : k * m ≤ m + n ↔ (k-1) * m ≤ n := by
+  match k with
+  | 0 =>
+    simp
+  | succ k =>
+    simp [succ_mul, Nat.add_comm _ m, Nat.add_le_add_iff_left]
+
+theorem succ_mul_succ_eq (a b : Nat) : succ a * succ b = a * b + a + b + 1 := by
+  rw [mul_succ, succ_mul, Nat.add_right_comm _ a]; rfl
+
+protected theorem mul_self_sub_mul_self_eq (a b : Nat) : a * a - b * b = (a + b) * (a - b) := by
+  rw [Nat.mul_sub_left_distrib, Nat.right_distrib, Nat.right_distrib, Nat.mul_comm b a,
+    Nat.sub_add_eq, Nat.add_sub_cancel]
+
+protected theorem pos_of_mul_pos_left {a b : Nat} (h : 0 < a * b) : 0 < b := by
+  apply Decidable.by_contra
+  intros
+  simp_all
+
+protected theorem pos_of_mul_pos_right {a b : Nat} (h : 0 < a * b) : 0 < a := by
+  apply Decidable.by_contra
+  intros
+  simp_all
+
+@[simp] protected theorem mul_pos_iff_of_pos_left {a b : Nat} (h : 0 < a) :
+    0 < a * b ↔ 0 < b :=
+  ⟨Nat.pos_of_mul_pos_left, Nat.mul_pos h⟩
+
+@[simp] protected theorem mul_pos_iff_of_pos_right {a b : Nat} (h : 0 < b) :
+    0 < a * b ↔ 0 < a :=
+  ⟨Nat.pos_of_mul_pos_right, fun w => Nat.mul_pos w h⟩
+
+/-! ### div/mod -/
+
+theorem mod_two_eq_zero_or_one (n : Nat) : n % 2 = 0 ∨ n % 2 = 1 :=
+  match n % 2, @Nat.mod_lt n 2 (by decide) with
+  | 0, _ => .inl rfl
+  | 1, _ => .inr rfl
+
+theorem le_of_mod_lt {a b : Nat} (h : a % b < a) : b ≤ a :=
+  Nat.not_lt.1 fun hf => (ne_of_lt h).elim (Nat.mod_eq_of_lt hf)
+
+theorem mul_mod_mul_right (z x y : Nat) : (x * z) % (y * z) = (x % y) * z := by
+  rw [Nat.mul_comm x z, Nat.mul_comm y z, Nat.mul_comm (x % y) z]; apply mul_mod_mul_left
+
+theorem sub_mul_mod {x k n : Nat} (h₁ : n*k ≤ x) : (x - n*k) % n = x % n := by
+  match k with
+  | 0 => rw [Nat.mul_zero, Nat.sub_zero]
+  | succ k =>
+    have h₂ : n * k ≤ x := Nat.le_trans (le_add_right _ n) h₁
+    have h₄ : x - n * k ≥ n := by
+      apply Nat.le_of_add_le_add_right (b := n * k)
+      rw [Nat.sub_add_cancel h₂]
+      simp [mul_succ, Nat.add_comm] at h₁; simp [h₁]
+    rw [mul_succ, ← Nat.sub_sub, ← mod_eq_sub_mod h₄, sub_mul_mod h₂]
+
+@[simp] theorem mod_mod (a n : Nat) : (a % n) % n = a % n :=
+  match eq_zero_or_pos n with
+  | .inl n0 => by simp [n0, mod_zero]
+  | .inr npos => Nat.mod_eq_of_lt (mod_lt _ npos)
+
+theorem mul_mod (a b n : Nat) : a * b % n = (a % n) * (b % n) % n := by
+  rw (config := {occs := .pos [1]}) [← mod_add_div a n]
+  rw (config := {occs := .pos [1]}) [← mod_add_div b n]
+  rw [Nat.add_mul, Nat.mul_add, Nat.mul_add,
+    Nat.mul_assoc, Nat.mul_assoc, ← Nat.mul_add n, add_mul_mod_self_left,
+    Nat.mul_comm _ (n * (b / n)), Nat.mul_assoc, add_mul_mod_self_left]
+
+@[simp] theorem mod_add_mod (m n k : Nat) : (m % n + k) % n = (m + k) % n := by
+  have := (add_mul_mod_self_left (m % n + k) n (m / n)).symm
+  rwa [Nat.add_right_comm, mod_add_div] at this
+
+@[simp] theorem add_mod_mod (m n k : Nat) : (m + n % k) % k = (m + n) % k := by
+  rw [Nat.add_comm, mod_add_mod, Nat.add_comm]
+
+theorem add_mod (a b n : Nat) : (a + b) % n = ((a % n) + (b % n)) % n := by
+  rw [add_mod_mod, mod_add_mod]
+
+/-! ### pow -/
+
+theorem pow_succ' {m n : Nat} : m ^ n.succ = m * m ^ n := by
+  rw [Nat.pow_succ, Nat.mul_comm]
+
+@[simp] theorem pow_eq {m n : Nat} : m.pow n = m ^ n := rfl
+
+theorem one_shiftLeft (n : Nat) : 1 <<< n = 2 ^ n := by rw [shiftLeft_eq, Nat.one_mul]
+
+attribute [simp] Nat.pow_zero
+
+protected theorem zero_pow {n : Nat} (H : 0 < n) : 0 ^ n = 0 := by
+  match n with
+  | 0 => contradiction
+  | n+1 => rw [Nat.pow_succ, Nat.mul_zero]
+
+@[simp] protected theorem one_pow (n : Nat) : 1 ^ n = 1 := by
+  induction n with
+  | zero => rfl
+  | succ _ ih => rw [Nat.pow_succ, Nat.mul_one, ih]
+
+@[simp] protected theorem pow_one (a : Nat) : a ^ 1 = a := by
+  rw [Nat.pow_succ, Nat.pow_zero, Nat.one_mul]
+
+protected theorem pow_two (a : Nat) : a ^ 2 = a * a := by rw [Nat.pow_succ, Nat.pow_one]
+
+protected theorem pow_add (a m n : Nat) : a ^ (m + n) = a ^ m * a ^ n := by
+  induction n with
+  | zero => rw [Nat.add_zero, Nat.pow_zero, Nat.mul_one]
+  | succ _ ih => rw [Nat.add_succ, Nat.pow_succ, Nat.pow_succ, ih, Nat.mul_assoc]
+
+protected theorem pow_add' (a m n : Nat) : a ^ (m + n) = a ^ n * a ^ m := by
+  rw [← Nat.pow_add, Nat.add_comm]
+
+protected theorem pow_mul (a m n : Nat) : a ^ (m * n) = (a ^ m) ^ n := by
+  induction n with
+  | zero => rw [Nat.mul_zero, Nat.pow_zero, Nat.pow_zero]
+  | succ _ ih => rw [Nat.mul_succ, Nat.pow_add, Nat.pow_succ, ih]
+
+protected theorem pow_mul' (a m n : Nat) : a ^ (m * n) = (a ^ n) ^ m := by
+  rw [← Nat.pow_mul, Nat.mul_comm]
+
+protected theorem pow_right_comm (a m n : Nat) : (a ^ m) ^ n = (a ^ n) ^ m := by
+  rw [← Nat.pow_mul, Nat.pow_mul']
+
+protected theorem mul_pow (a b n : Nat) : (a * b) ^ n = a ^ n * b ^ n := by
+  induction n with
+  | zero => rw [Nat.pow_zero, Nat.pow_zero, Nat.pow_zero, Nat.mul_one]
+  | succ _ ih => rw [Nat.pow_succ, Nat.pow_succ, Nat.pow_succ, Nat.mul_mul_mul_comm, ih]
+
+protected abbrev pow_le_pow_left := @pow_le_pow_of_le_left
+protected abbrev pow_le_pow_right := @pow_le_pow_of_le_right
+
+protected theorem one_lt_two_pow (h : n ≠ 0) : 1 < 2 ^ n :=
+  match n, h with
+  | n+1, _ => by
+    rw [Nat.pow_succ', ← Nat.one_mul 1]
+    exact Nat.mul_lt_mul_of_lt_of_le' (by decide) (Nat.two_pow_pos n) (by decide)
+
+@[simp] protected theorem one_lt_two_pow_iff : 1 < 2 ^ n ↔ n ≠ 0 :=
+  ⟨(by intro h p; subst p; simp at h), Nat.one_lt_two_pow⟩
+
+protected theorem one_le_two_pow : 1 ≤ 2 ^ n :=
+  if h : n = 0 then
+    by subst h; simp
+  else
+    Nat.le_of_lt (Nat.one_lt_two_pow h)
+
+protected theorem pow_pos (h : 0 < a) : 0 < a^n :=
+  match n with
+  | 0 => Nat.zero_lt_one
+  | _ + 1 => Nat.mul_pos (Nat.pow_pos h) h
+
+protected theorem pow_lt_pow_succ (h : 1 < a) : a ^ n < a ^ (n + 1) := by
+  rw [← Nat.mul_one (a^n), Nat.pow_succ]
+  exact Nat.mul_lt_mul_of_le_of_lt (Nat.le_refl _) h (Nat.pow_pos (Nat.lt_trans Nat.zero_lt_one h))
+
+protected theorem pow_lt_pow_of_lt {a n m : Nat} (h : 1 < a) (w : n < m) : a ^ n < a ^ m := by
+  have := Nat.exists_eq_add_of_lt w
+  cases this
+  case intro k p =>
+  rw [Nat.add_right_comm] at p
+  subst p
+  rw [Nat.pow_add, ← Nat.mul_one (a^n)]
+  have t : 0 < a ^ k := Nat.pow_pos (Nat.lt_trans Nat.zero_lt_one h)
+  exact Nat.mul_lt_mul_of_lt_of_le (Nat.pow_lt_pow_succ h) t t
+
+protected theorem pow_le_pow_of_le {a n m : Nat} (h : 1 < a) (w : n ≤ m) : a ^ n ≤ a ^ m := by
+  cases Nat.lt_or_eq_of_le w
+  case inl lt =>
+    exact Nat.le_of_lt (Nat.pow_lt_pow_of_lt h lt)
+  case inr eq =>
+    subst eq
+    exact Nat.le_refl _
+
+protected theorem pow_le_pow_iff_right {a n m : Nat} (h : 1 < a) :
+    a ^ n ≤ a ^ m ↔ n ≤ m := by
+  constructor
+  · apply Decidable.by_contra
+    intros w
+    simp [Decidable.not_imp_iff_and_not] at w
+    apply Nat.lt_irrefl (a ^ n)
+    exact Nat.lt_of_le_of_lt w.1 (Nat.pow_lt_pow_of_lt h w.2)
+  · intro w
+    cases Nat.eq_or_lt_of_le w
+    case inl eq => subst eq; apply Nat.le_refl
+    case inr lt => exact Nat.le_of_lt (Nat.pow_lt_pow_of_lt h lt)
+
+protected theorem pow_lt_pow_iff_right {a n m : Nat} (h : 1 < a) :
+    a ^ n < a ^ m ↔ n < m := by
+  constructor
+  · apply Decidable.by_contra
+    intros w
+    simp at w
+    apply Nat.lt_irrefl (a ^ n)
+    exact Nat.lt_of_lt_of_le w.1 (Nat.pow_le_pow_of_le h w.2)
+  · intro w
+    exact Nat.pow_lt_pow_of_lt h w
+
+/-! ### log2 -/
+
+theorem le_log2 (h : n ≠ 0) : k ≤ n.log2 ↔ 2 ^ k ≤ n := by
+  match k with
+  | 0 => simp [show 1 ≤ n from Nat.pos_of_ne_zero h]
+  | k+1 =>
+    rw [log2]; split
+    · have n0 : 0 < n / 2 := (Nat.le_div_iff_mul_le (by decide)).2 ‹_›
+      simp only [Nat.add_le_add_iff_right, le_log2 (Nat.ne_of_gt n0), le_div_iff_mul_le,
+        Nat.pow_succ]
+      exact Nat.le_div_iff_mul_le (by decide)
+    · simp only [le_zero_eq, succ_ne_zero, false_iff]
+      refine mt (Nat.le_trans ?_) ‹_›
+      exact Nat.pow_le_pow_of_le_right Nat.zero_lt_two (Nat.le_add_left 1 k)
+
+theorem log2_lt (h : n ≠ 0) : n.log2 < k ↔ n < 2 ^ k := by
+  rw [← Nat.not_le, ← Nat.not_le, le_log2 h]
+
+theorem log2_self_le (h : n ≠ 0) : 2 ^ n.log2 ≤ n := (le_log2 h).1 (Nat.le_refl _)
+
+theorem lt_log2_self : n < 2 ^ (n.log2 + 1) :=
+  match n with
+  | 0 => Nat.zero_lt_two
+  | n+1 => (log2_lt n.succ_ne_zero).1 (Nat.le_refl _)
+
+/-! ### dvd -/
+
+protected theorem eq_mul_of_div_eq_right {a b c : Nat} (H1 : b ∣ a) (H2 : a / b = c) :
+    a = b * c := by
+  rw [← H2, Nat.mul_div_cancel' H1]
+
+protected theorem div_eq_iff_eq_mul_right {a b c : Nat} (H : 0 < b) (H' : b ∣ a) :
+    a / b = c ↔ a = b * c :=
+  ⟨Nat.eq_mul_of_div_eq_right H', Nat.div_eq_of_eq_mul_right H⟩
+
+protected theorem div_eq_iff_eq_mul_left {a b c : Nat} (H : 0 < b) (H' : b ∣ a) :
+    a / b = c ↔ a = c * b := by
+  rw [Nat.mul_comm]; exact Nat.div_eq_iff_eq_mul_right H H'
+
+theorem pow_dvd_pow_iff_pow_le_pow {k l : Nat} :
+    ∀ {x : Nat}, 0 < x → (x ^ k ∣ x ^ l ↔ x ^ k ≤ x ^ l)
+  | x + 1, w => by
+    constructor
+    · intro a
+      exact le_of_dvd (Nat.pow_pos (succ_pos x)) a
+    · intro a
+      cases x
+      case zero => simp
+      case succ x =>
+        have le :=
+          (Nat.pow_le_pow_iff_right (Nat.succ_le_succ (Nat.succ_le_succ (Nat.zero_le _)))).mp a
+        refine ⟨(x + 2) ^ (l - k), ?_⟩
+        rw [← Nat.pow_add, Nat.add_comm k, Nat.sub_add_cancel le]
+
+/-- If `1 < x`, then `x^k` divides `x^l` if and only if `k` is at most `l`. -/
+theorem pow_dvd_pow_iff_le_right {x k l : Nat} (w : 1 < x) : x ^ k ∣ x ^ l ↔ k ≤ l := by
+  rw [pow_dvd_pow_iff_pow_le_pow (lt_of_succ_lt w), Nat.pow_le_pow_iff_right w]
+
+theorem pow_dvd_pow_iff_le_right' {b k l : Nat} : (b + 2) ^ k ∣ (b + 2) ^ l ↔ k ≤ l :=
+  pow_dvd_pow_iff_le_right (Nat.lt_of_sub_eq_succ rfl)
+
+protected theorem pow_dvd_pow {m n : Nat} (a : Nat) (h : m ≤ n) : a ^ m ∣ a ^ n := by
+  cases Nat.exists_eq_add_of_le h
+  case intro k p =>
+    subst p
+    rw [Nat.pow_add]
+    apply Nat.dvd_mul_right
+
+protected theorem pow_sub_mul_pow (a : Nat) {m n : Nat} (h : m ≤ n) :
+    a ^ (n - m) * a ^ m = a ^ n := by
+  rw [← Nat.pow_add, Nat.sub_add_cancel h]
+
+theorem pow_dvd_of_le_of_pow_dvd {p m n k : Nat} (hmn : m ≤ n) (hdiv : p ^ n ∣ k) : p ^ m ∣ k :=
+  Nat.dvd_trans (Nat.pow_dvd_pow _ hmn) hdiv
+
+theorem dvd_of_pow_dvd {p k m : Nat} (hk : 1 ≤ k) (hpk : p ^ k ∣ m) : p ∣ m := by
+  rw [← Nat.pow_one p]; exact pow_dvd_of_le_of_pow_dvd hk hpk
+
+protected theorem pow_div {x m n : Nat} (h : n ≤ m) (hx : 0 < x) : x ^ m / x ^ n = x ^ (m - n) := by
+  rw [Nat.div_eq_iff_eq_mul_left (Nat.pow_pos hx) (Nat.pow_dvd_pow _ h), Nat.pow_sub_mul_pow _ h]
+
+/-! ### shiftLeft and shiftRight -/
+
+@[simp] theorem shiftLeft_zero : n <<< 0 = n := rfl
+
+/-- Shiftleft on successor with multiple moved inside. -/
+theorem shiftLeft_succ_inside (m n : Nat) : m <<< (n+1) = (2*m) <<< n := rfl
+
+/-- Shiftleft on successor with multiple moved to outside. -/
+theorem shiftLeft_succ : ∀(m n), m <<< (n + 1) = 2 * (m <<< n)
+| m, 0 => rfl
+| m, k + 1 => by
+  rw [shiftLeft_succ_inside _ (k+1)]
+  rw [shiftLeft_succ _ k, shiftLeft_succ_inside]
+
+/-- Shiftright on successor with division moved inside. -/
+theorem shiftRight_succ_inside : ∀m n, m >>> (n+1) = (m/2) >>> n
+| m, 0 => rfl
+| m, k + 1 => by
+  rw [shiftRight_succ _ (k+1)]
+  rw [shiftRight_succ_inside _ k, shiftRight_succ]
+
+@[simp] theorem zero_shiftLeft : ∀ n, 0 <<< n = 0
+  | 0 => by simp [shiftLeft]
+  | n + 1 => by simp [shiftLeft, zero_shiftLeft n, shiftLeft_succ]
+
+@[simp] theorem zero_shiftRight : ∀ n, 0 >>> n = 0
+  | 0 => by simp [shiftRight]
+  | n + 1 => by simp [shiftRight, zero_shiftRight n, shiftRight_succ]
+
+theorem shiftLeft_shiftLeft (m n : Nat) : ∀ k, (m <<< n) <<< k = m <<< (n + k)
+  | 0 => rfl
+  | k + 1 => by simp [← Nat.add_assoc, shiftLeft_shiftLeft _ _ k, shiftLeft_succ]
+
+theorem mul_add_div {m : Nat} (m_pos : m > 0) (x y : Nat) : (m * x + y) / m = x + y / m := by
+  match x with
+  | 0 => simp
+  | x + 1 =>
+    rw [Nat.mul_succ, Nat.add_assoc _ m, mul_add_div m_pos x (m+y), div_eq]
+    simp_arith [m_pos]; rw [Nat.add_comm, Nat.add_sub_cancel]
+
+theorem mul_add_mod (m x y : Nat) : (m * x + y) % m = y % m := by
+  match x with
+  | 0 => simp
+  | x + 1 =>
+    simp [Nat.mul_succ, Nat.add_assoc _ m, mul_add_mod _ x]
+
+@[simp] theorem mod_div_self (m n : Nat) : m % n / n = 0 := by
+  cases n
+  · exact (m % 0).div_zero
+  · case succ n => exact Nat.div_eq_of_lt (m.mod_lt n.succ_pos)
+
+/-! ### Decidability of predicates -/
+
+instance decidableBallLT :
+  ∀ (n : Nat) (P : ∀ k, k < n → Prop) [∀ n h, Decidable (P n h)], Decidable (∀ n h, P n h)
+| 0, _, _ => isTrue fun _ => (by cases ·)
+| n + 1, P, H =>
+  match decidableBallLT n (P · <| lt_succ_of_lt ·) with
+  | isFalse h => isFalse (h fun _ _ => · _ _)
+  | isTrue h =>
+    match H n Nat.le.refl with
+    | isFalse p => isFalse (p <| · _ _)
+    | isTrue p => isTrue fun _ h' => (Nat.lt_succ_iff_lt_or_eq.1 h').elim (h _) fun hn => hn ▸ p
+
+instance decidableForallFin (P : Fin n → Prop) [DecidablePred P] : Decidable (∀ i, P i) :=
+  decidable_of_iff (∀ k h, P ⟨k, h⟩) ⟨fun m ⟨k, h⟩ => m k h, fun m k h => m ⟨k, h⟩⟩
+
+instance decidableBallLE (n : Nat) (P : ∀ k, k ≤ n → Prop) [∀ n h, Decidable (P n h)] :
+    Decidable (∀ n h, P n h) :=
+  decidable_of_iff (∀ (k) (h : k < succ n), P k (le_of_lt_succ h))
+    ⟨fun m k h => m k (lt_succ_of_le h), fun m k _ => m k _⟩
+
+instance decidableExistsLT [h : DecidablePred p] : DecidablePred fun n => ∃ m : Nat, m < n ∧ p m
+  | 0 => isFalse (by simp only [not_lt_zero, false_and, exists_const, not_false_eq_true])
+  | n + 1 =>
+    @decidable_of_decidable_of_iff _ _ (@instDecidableOr _ _ (decidableExistsLT (p := p) n) (h n))
+      (by simp only [Nat.lt_succ_iff_lt_or_eq, or_and_right, exists_or, exists_eq_left])
+
+instance decidableExistsLE [DecidablePred p] : DecidablePred fun n => ∃ m : Nat, m ≤ n ∧ p m :=
+  fun n => decidable_of_iff (∃ m, m < n + 1 ∧ p m)
+    (exists_congr fun _ => and_congr_left' Nat.lt_succ_iff)

src/Init/Data/Nat/Linear.lean

@@ -4,11 +4,7 @@ Released under Apache 2.0 license as described in the file LICENSE.
 Authors: Leonardo de Moura
 -/
 prelude
-import Init.Coe
-import Init.Classical
-import Init.SimpLemmas
-import Init.Data.Nat.Basic
-import Init.Data.List.Basic
+import Init.ByCases
 import Init.Data.Prod
 
 namespace Nat.Linear
@@ -539,13 +535,13 @@ theorem Expr.eq_of_toNormPoly (ctx : Context) (a b : Expr) (h : a.toNormPoly = b
 theorem Expr.of_cancel_eq (ctx : Context) (a b c d : Expr) (h : Poly.cancel a.toNormPoly b.toNormPoly = (c.toPoly, d.toPoly)) : (a.denote ctx = b.denote ctx) = (c.denote ctx = d.denote ctx) := by
   have := Poly.denote_eq_cancel_eq ctx a.toNormPoly b.toNormPoly
   rw [h] at this
-  simp [toNormPoly, Poly.norm, Poly.denote_eq] at this
+  simp [toNormPoly, Poly.norm, Poly.denote_eq, -eq_iff_iff] at this
   exact this.symm
 
 theorem Expr.of_cancel_le (ctx : Context) (a b c d : Expr) (h : Poly.cancel a.toNormPoly b.toNormPoly = (c.toPoly, d.toPoly)) : (a.denote ctx ≤ b.denote ctx) = (c.denote ctx ≤ d.denote ctx) := by
   have := Poly.denote_le_cancel_eq ctx a.toNormPoly b.toNormPoly
   rw [h] at this
-  simp [toNormPoly, Poly.norm,Poly.denote_le] at this
+  simp [toNormPoly, Poly.norm,Poly.denote_le, -eq_iff_iff] at this
   exact this.symm
 
 theorem Expr.of_cancel_lt (ctx : Context) (a b c d : Expr) (h : Poly.cancel a.inc.toNormPoly b.toNormPoly = (c.inc.toPoly, d.toPoly)) : (a.denote ctx < b.denote ctx) = (c.denote ctx < d.denote ctx) :=
@@ -584,13 +580,13 @@ attribute [-simp] Nat.right_distrib Nat.left_distrib
 
 theorem PolyCnstr.denote_mul (ctx : Context) (k : Nat) (c : PolyCnstr) : (c.mul (k+1)).denote ctx = c.denote ctx := by
   cases c; rename_i eq lhs rhs
-  have : k ≠ 0 → k + 1 ≠ 1 := by intro h; match k with | 0 => contradiction | k+1 => simp; apply Nat.succ_ne_zero
+  have : k ≠ 0 → k + 1 ≠ 1 := by intro h; match k with | 0 => contradiction | k+1 => simp [Nat.succ.injEq]
   have : ¬ (k == 0) → (k + 1 == 1) = false := fun h => beq_false_of_ne (this (ne_of_beq_false (Bool.of_not_eq_true h)))
   have : ¬ ((k + 1 == 0) = true)  := fun h => absurd (eq_of_beq h) (Nat.succ_ne_zero k)
   have : (1 == (0 : Nat)) = false := rfl
   have : (1 == (1 : Nat)) = true  := rfl
   by_cases he : eq = true <;> simp [he, PolyCnstr.mul, PolyCnstr.denote, Poly.denote_le, Poly.denote_eq]
-     <;> by_cases hk : k == 0 <;> (try simp [eq_of_beq hk]) <;> simp [*] <;> apply propext <;> apply Iff.intro <;> intro h
+     <;> by_cases hk : k == 0 <;> (try simp [eq_of_beq hk]) <;> simp [*] <;> apply Iff.intro <;> intro h
   · exact Nat.eq_of_mul_eq_mul_left (Nat.zero_lt_succ _) h
   · rw [h]
   · exact Nat.le_of_mul_le_mul_left h (Nat.zero_lt_succ _)
@@ -637,20 +633,18 @@ theorem Poly.of_isNonZero (ctx : Context) {p : Poly} (h : isNonZero p = true) :
 theorem PolyCnstr.eq_false_of_isUnsat (ctx : Context) {c : PolyCnstr} : c.isUnsat → c.denote ctx = False := by
   cases c; rename_i eq lhs rhs
   simp [isUnsat]
-  by_cases he : eq = true <;> simp [he, denote, Poly.denote_eq, Poly.denote_le]
+  by_cases he : eq = true <;> simp [he, denote, Poly.denote_eq, Poly.denote_le, -and_imp]
   · intro
       | Or.inl ⟨h₁, h₂⟩ => simp [Poly.of_isZero, h₁]; have := Nat.not_eq_zero_of_lt (Poly.of_isNonZero ctx h₂); simp [this.symm]
       | Or.inr ⟨h₁, h₂⟩ => simp [Poly.of_isZero, h₂]; have := Nat.not_eq_zero_of_lt (Poly.of_isNonZero ctx h₁); simp [this]
   · intro ⟨h₁, h₂⟩
     simp [Poly.of_isZero, h₂]
-    have := Nat.not_eq_zero_of_lt (Poly.of_isNonZero ctx h₁)
-    simp [this]
-    done
+    exact Poly.of_isNonZero ctx h₁
 
 theorem PolyCnstr.eq_true_of_isValid (ctx : Context) {c : PolyCnstr} : c.isValid → c.denote ctx = True := by
   cases c; rename_i eq lhs rhs
   simp [isValid]
-  by_cases he : eq = true <;> simp [he, denote, Poly.denote_eq, Poly.denote_le]
+  by_cases he : eq = true <;> simp [he, denote, Poly.denote_eq, Poly.denote_le, -and_imp]
   · intro ⟨h₁, h₂⟩
     simp [Poly.of_isZero, h₁, h₂]
   · intro h
@@ -658,12 +652,12 @@ theorem PolyCnstr.eq_true_of_isValid (ctx : Context) {c : PolyCnstr} : c.isValid
 
 theorem ExprCnstr.eq_false_of_isUnsat (ctx : Context) (c : ExprCnstr) (h : c.toNormPoly.isUnsat) : c.denote ctx = False := by
   have := PolyCnstr.eq_false_of_isUnsat ctx h
-  simp at this
+  simp [-eq_iff_iff] at this
   assumption
 
 theorem ExprCnstr.eq_true_of_isValid (ctx : Context) (c : ExprCnstr) (h : c.toNormPoly.isValid) : c.denote ctx = True := by
   have := PolyCnstr.eq_true_of_isValid ctx h
-  simp at this
+  simp [-eq_iff_iff] at this
   assumption
 
 theorem Certificate.of_combineHyps (ctx : Context) (c : PolyCnstr) (cs : Certificate) (h : (combineHyps c cs).denote ctx → False) : c.denote ctx → cs.denote ctx := by
@@ -712,7 +706,7 @@ theorem Poly.denote_toExpr (ctx : Context) (p : Poly) : p.toExpr.denote ctx = p.
 
 theorem ExprCnstr.eq_of_toNormPoly_eq (ctx : Context) (c d : ExprCnstr) (h : c.toNormPoly == d.toPoly) : c.denote ctx = d.denote ctx := by
   have h := congrArg (PolyCnstr.denote ctx) (eq_of_beq h)
-  simp at h
+  simp [-eq_iff_iff] at h
   assumption
 
 theorem Expr.eq_of_toNormPoly_eq (ctx : Context) (e e' : Expr) (h : e.toNormPoly == e'.toPoly) : e.denote ctx = e'.denote ctx := by

src/Init/Data/Nat/Log2.lean

@@ -4,7 +4,6 @@ Released under Apache 2.0 license as described in the file LICENSE.
 Authors: Gabriel Ebner
 -/
 prelude
-import Init.NotationExtra
 import Init.Data.Nat.Linear
 
 namespace Nat

src/Init/Data/Nat/MinMax.lean

@@ -0,0 +1,56 @@
+/-
+Copyright (c) 2016 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Leonardo de Moura, Jeremy Avigad, Mario Carneiro
+-/
+prelude
+import Init.ByCases
+
+namespace Nat
+
+/-! # min lemmas -/
+
+protected theorem min_eq_min (a : Nat) : Nat.min a b = min a b := rfl
+
+protected theorem min_comm (a b : Nat) : min a b = min b a := by
+  match Nat.lt_trichotomy a b with
+  | .inl h => simp [Nat.min_def, h, Nat.le_of_lt, Nat.not_le_of_lt]
+  | .inr (.inl h) => simp [Nat.min_def, h]
+  | .inr (.inr h) => simp [Nat.min_def, h, Nat.le_of_lt, Nat.not_le_of_lt]
+
+protected theorem min_le_right (a b : Nat) : min a b ≤ b := by
+  by_cases (a <= b) <;> simp [Nat.min_def, *]
+protected theorem min_le_left (a b : Nat) : min a b ≤ a :=
+  Nat.min_comm .. ▸ Nat.min_le_right ..
+
+protected theorem min_eq_left {a b : Nat} (h : a ≤ b) : min a b = a := if_pos h
+protected theorem min_eq_right {a b : Nat} (h : b ≤ a) : min a b = b :=
+  Nat.min_comm .. ▸ Nat.min_eq_left h
+
+protected theorem le_min_of_le_of_le {a b c : Nat} : a ≤ b → a ≤ c → a ≤ min b c := by
+  intros; cases Nat.le_total b c with
+  | inl h => rw [Nat.min_eq_left h]; assumption
+  | inr h => rw [Nat.min_eq_right h]; assumption
+
+protected theorem le_min {a b c : Nat} : a ≤ min b c ↔ a ≤ b ∧ a ≤ c :=
+  ⟨fun h => ⟨Nat.le_trans h (Nat.min_le_left ..), Nat.le_trans h (Nat.min_le_right ..)⟩,
+   fun ⟨h₁, h₂⟩ => Nat.le_min_of_le_of_le h₁ h₂⟩
+
+protected theorem lt_min {a b c : Nat} : a < min b c ↔ a < b ∧ a < c := Nat.le_min
+
+/-! # max lemmas -/
+
+protected theorem max_eq_max (a : Nat) : Nat.max a b = max a b := rfl
+
+protected theorem max_comm (a b : Nat) : max a b = max b a := by
+  simp only [Nat.max_def]
+  by_cases h₁ : a ≤ b <;> by_cases h₂ : b ≤ a <;> simp [h₁, h₂]
+  · exact Nat.le_antisymm h₂ h₁
+  · cases not_or_intro h₁ h₂ <| Nat.le_total ..
+
+protected theorem le_max_left ( a b : Nat) : a ≤ max a b := by
+  by_cases (a <= b) <;> simp [Nat.max_def, *]
+protected theorem le_max_right (a b : Nat) : b ≤ max a b :=
+   Nat.max_comm .. ▸ Nat.le_max_left ..
+
+end Nat

src/Init/Data/Nat/Mod.lean

@@ -0,0 +1,76 @@
+/-
+Copyright (c) 2024 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Scott Morrison
+-/
+prelude
+import Init.Omega
+
+/-!
+# Further results about `mod`.
+
+This file proves some results about `mod` that are useful for bitblasting,
+in particular
+`Nat.mod_mul : x % (a * b) = x % a + a * (x / a % b)`
+and its corollary
+`Nat.mod_pow_succ : x % b ^ (k + 1) = x % b ^ k + b ^ k * ((x / b ^ k) % b)`.
+
+It contains the necesssary preliminary results relating order and `*` and `/`,
+which should probably be moved to their own file.
+-/
+
+namespace Nat
+
+@[simp] protected theorem mul_lt_mul_left (a0 : 0 < a) : a * b < a * c ↔ b < c := by
+  induction a with
+  | zero => simp_all
+  | succ a ih =>
+    cases a
+    · simp
+    · simp_all [succ_eq_add_one, Nat.right_distrib]
+      omega
+
+@[simp] protected theorem mul_lt_mul_right (a0 : 0 < a) : b * a < c * a ↔ b < c := by
+  rw [Nat.mul_comm b a, Nat.mul_comm c a, Nat.mul_lt_mul_left a0]
+
+protected theorem lt_of_mul_lt_mul_left {a b c : Nat} (h : a * b < a * c) : b < c := by
+  cases a <;> simp_all
+
+protected theorem lt_of_mul_lt_mul_right {a b c : Nat} (h : b * a < c * a) : b < c := by
+  rw [Nat.mul_comm b a, Nat.mul_comm c a] at h
+  exact Nat.lt_of_mul_lt_mul_left h
+
+protected theorem div_lt_of_lt_mul {m n k : Nat} (h : m < n * k) : m / n < k :=
+  Nat.lt_of_mul_lt_mul_left <|
+    calc
+      n * (m / n) ≤ m % n + n * (m / n) := Nat.le_add_left _ _
+      _ = m := mod_add_div _ _
+      _ < n * k := h
+
+theorem mod_mul_right_div_self (m n k : Nat) : m % (n * k) / n = m / n % k := by
+  rcases Nat.eq_zero_or_pos n with (rfl | hn); simp [mod_zero]
+  rcases Nat.eq_zero_or_pos k with (rfl | hk); simp [mod_zero]
+  conv => rhs; rw [← mod_add_div m (n * k)]
+  rw [Nat.mul_assoc, add_mul_div_left _ _ hn, add_mul_mod_self_left,
+    mod_eq_of_lt (Nat.div_lt_of_lt_mul (mod_lt _ (Nat.mul_pos hn hk)))]
+
+theorem mod_mul_left_div_self (m n k : Nat) : m % (k * n) / n = m / n % k := by
+  rw [Nat.mul_comm k n, mod_mul_right_div_self]
+
+@[simp 1100]
+theorem mod_mul_right_mod (a b c : Nat) : a % (b * c) % b = a % b :=
+  Nat.mod_mod_of_dvd a (Nat.dvd_mul_right b c)
+
+@[simp 1100]
+theorem mod_mul_left_mod (a b c : Nat) : a % (b * c) % c = a % c :=
+  Nat.mod_mod_of_dvd a (Nat.mul_comm _ _ ▸ Nat.dvd_mul_left c b)
+
+theorem mod_mul {a b x : Nat} : x % (a * b) = x % a + a * (x / a % b) := by
+  rw [Nat.add_comm, ← Nat.div_add_mod (x % (a*b)) a, Nat.mod_mul_right_mod,
+    Nat.mod_mul_right_div_self]
+
+theorem mod_pow_succ {x b k : Nat} :
+    x % b ^ (k + 1) = x % b ^ k + b ^ k * ((x / b ^ k) % b) := by
+  rw [Nat.pow_succ, Nat.mod_mul]
+
+end Nat

src/Init/Data/Nat/Power2.lean

@@ -8,6 +8,8 @@ import Init.Data.Nat.Linear
 
 namespace Nat
 
+protected theorem two_pow_pos (w : Nat) : 0 < 2^w := Nat.pos_pow_of_pos _ (by decide)
+
 theorem nextPowerOfTwo_dec {n power : Nat} (h₁ : power > 0) (h₂ : power < n) : n - power * 2 < n - power := by
   have : power * 2 = power + power := by simp_arith
   rw [this, Nat.sub_add_eq]

src/Init/Data/Nat/Simproc.lean

@@ -0,0 +1,108 @@
+/-
+Copyright (c) 2023 Lean FRO. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Joe Hendrix
+-/
+prelude
+import Init.Data.Bool
+import Init.Data.Nat.Basic
+import Init.Data.Nat.Lemmas
+
+/-!
+This contains lemmas used by the Nat simprocs for simplifying arithmetic
+addition offsets.
+-/
+namespace Nat.Simproc
+
+/- Sub proofs -/
+
+theorem sub_add_eq_comm (a b c : Nat) : a - (b + c) = a - c - b := by
+  rw [Nat.add_comm b c]
+  exact Nat.sub_add_eq a c b
+
+theorem add_sub_add_le (a c : Nat) {b d : Nat} (h : b ≤ d) : a + b - (c + d) = a - (c + (d-b)) := by
+  induction b generalizing a c d with
+  | zero =>
+    simp
+  | succ b ind =>
+    match d with
+    | 0 =>
+      contradiction
+    | d + 1 =>
+      have g := Nat.le_of_succ_le_succ h
+      rw [Nat.add_succ a, Nat.add_succ c, Nat.succ_sub_succ, Nat.succ_sub_succ,
+          ind _ _ g]
+
+theorem add_sub_add_ge (a c : Nat) {b d : Nat} (h : b ≥ d) : a + b - (c + d) = a + (b - d) - c := by
+  rw [Nat.add_comm c d, Nat.sub_add_eq, Nat.add_sub_assoc h a]
+
+theorem add_sub_le (a : Nat) {b c : Nat} (h : b ≤ c) : a + b - c = a - (c - b) := by
+  have p := add_sub_add_le a 0 h
+  simp only [Nat.zero_add] at p
+  exact p
+
+/- Eq proofs -/
+
+theorem add_eq_gt (a : Nat) {b c : Nat} (h : b > c) : (a + b = c) = False :=
+  eq_false (Nat.ne_of_gt (Nat.lt_of_lt_of_le h (le_add_left b a)))
+
+theorem eq_add_gt (a : Nat) {b c : Nat} (h : c > a) : (a = b + c) = False := by
+  rw [@Eq.comm Nat a (b + c)]
+  exact add_eq_gt b h
+
+theorem add_eq_add_le (a c : Nat) {b d : Nat} (h : b ≤ d) : (a + b = c + d) = (a = c + (d - b)) := by
+  have g : b ≤ c + d := Nat.le_trans h (le_add_left d c)
+  rw [← Nat.add_sub_assoc h, @Eq.comm _ a, Nat.sub_eq_iff_eq_add g, @Eq.comm _ (a + b)]
+
+theorem add_eq_add_ge (a c : Nat) {b d : Nat} (h : b ≥ d) : (a + b = c + d) = (a + (b - d) = c) := by
+  rw [@Eq.comm _ (a + b) _, add_eq_add_le c a h, @Eq.comm _ _ c]
+
+theorem add_eq_le (a : Nat) {b c : Nat} (h : b ≤ c) : (a + b = c) = (a = c - b) := by
+  have r := add_eq_add_le a 0 h
+  simp only [Nat.zero_add] at r
+  exact r
+
+theorem eq_add_le {a : Nat} (b : Nat) {c : Nat} (h : c ≤ a) : (a = b + c) = (b = a - c) := by
+  rw [@Eq.comm Nat a (b + c)]
+  exact add_eq_le b h
+
+/- Lemmas for lifting Eq proofs to beq -/
+
+theorem beqEqOfEqEq {a b c d : Nat} (p : (a = b) = (c = d)) : (a == b) = (c == d) := by
+  simp only [Bool.beq_eq_decide_eq, p]
+
+theorem beqFalseOfEqFalse {a b : Nat} (p : (a = b) = False) : (a == b) = false := by
+  simp [Bool.beq_eq_decide_eq, p]
+
+theorem bneEqOfEqEq {a b c d : Nat} (p : (a = b) = (c = d)) : (a != b) = (c != d) := by
+  simp only [bne, beqEqOfEqEq p]
+
+theorem bneTrueOfEqFalse {a b : Nat} (p : (a = b) = False) : (a != b) = true := by
+  simp [bne, beqFalseOfEqFalse p]
+
+/- le proofs -/
+
+theorem add_le_add_le (a c : Nat) {b d : Nat} (h : b ≤ d) : (a + b ≤ c + d) = (a ≤ c + (d - b)) := by
+  rw [← Nat.add_sub_assoc h, Nat.le_sub_iff_add_le]
+  exact Nat.le_trans h (le_add_left d c)
+
+theorem add_le_add_ge (a c : Nat) {b d : Nat} (h : b ≥ d) : (a + b ≤ c + d) = (a + (b - d) ≤ c) := by
+  rw [← Nat.add_sub_assoc h, Nat.sub_le_iff_le_add]
+
+theorem add_le_le (a : Nat) {b c : Nat} (h : b ≤ c) : (a + b ≤ c) = (a ≤ c - b) := by
+  have r := add_le_add_le a 0 h
+  simp only [Nat.zero_add] at r
+  exact r
+
+theorem add_le_gt (a : Nat) {b c : Nat} (h : b > c) : (a + b ≤ c) = False :=
+  eq_false (Nat.not_le_of_gt (Nat.lt_of_lt_of_le h (le_add_left b a)))
+
+theorem le_add_le (a : Nat) {b c : Nat} (h : a ≤ c) : (a ≤ b + c) = True :=
+  eq_true (Nat.le_trans h (le_add_left c b))
+
+theorem le_add_ge (a : Nat) {b c : Nat} (h : a ≥ c) : (a ≤ b + c) = (a - c ≤ b) := by
+  have r := add_le_add_ge 0 b h
+  simp only [Nat.zero_add] at r
+  exact r
+
+end Nat.Simproc

src/Init/Data/Option.lean

@@ -7,3 +7,4 @@ prelude
 import Init.Data.Option.Basic
 import Init.Data.Option.BasicAux
 import Init.Data.Option.Instances
+import Init.Data.Option.Lemmas

src/Init/Data/Option/Basic.lean

@@ -1,7 +1,7 @@
 /-
 Copyright (c) 2014 Microsoft Corporation. All rights reserved.
 Released under Apache 2.0 license as described in the file LICENSE.
-Authors: Leonardo de Moura
+Authors: Leonardo de Moura, Mario Carneiro
 -/
 prelude
 import Init.Core
@@ -10,30 +10,53 @@ import Init.Coe
 
 namespace Option
 
-def toMonad [Monad m] [Alternative m] : Option α → m α
+deriving instance DecidableEq for Option
+deriving instance BEq for Option
+
+/-- Lifts an optional value to any `Alternative`, sending `none` to `failure`. -/
+def getM [Alternative m] : Option α → m α
   | none     => failure
   | some a   => pure a
 
+@[deprecated getM] def toMonad [Monad m] [Alternative m] : Option α → m α :=
+  getM
+
 @[inline] def toBool : Option α → Bool
   | some _ => true
   | none   => false
 
+/-- Returns `true` on `some x` and `false` on `none`. -/
 @[inline] def isSome : Option α → Bool
   | some _ => true
   | none   => false
 
+/-- Returns `true` on `none` and `false` on `some x`. -/
 @[inline] def isNone : Option α → Bool
   | some _ => false
   | none   => true
 
+/--
+`x?.isEqSome y` is equivalent to `x? == some y`, but avoids an allocation.
+-/
 @[inline] def isEqSome [BEq α] : Option α → α → Bool
   | some a, b => a == b
   | none,   _ => false
 
 @[inline] protected def bind : Option α → (α → Option β) → Option β
   | none,   _ => none
-  | some a, b => b a
+  | some a, f => f a
 
+/-- Runs `f` on `o`'s value, if any, and returns its result, or else returns `none`.  -/
+@[inline] protected def bindM [Monad m] (f : α → m (Option β)) (o : Option α) : m (Option β) := do
+  if let some a := o then
+    return (← f a)
+  else
+    return none
+
+/--
+Runs a monadic function `f` on an optional value.
+If the optional value is `none` the function is not called.
+-/
 @[inline] protected def mapM [Monad m] (f : α → m β) (o : Option α) : m (Option β) := do
   if let some a := o then
     return some (← f a)
@@ -43,18 +66,24 @@ def toMonad [Monad m] [Alternative m] : Option α → m α
 theorem map_id : (Option.map id : Option α → Option α) = id :=
   funext (fun o => match o with | none => rfl | some _ => rfl)
 
+/-- Keeps an optional value only if it satisfies the predicate `p`. -/
 @[always_inline, inline] protected def filter (p : α → Bool) : Option α → Option α
   | some a => if p a then some a else none
   | none   => none
 
+/-- Checks that an optional value satisfies a predicate `p` or is `none`. -/
 @[always_inline, inline] protected def all (p : α → Bool) : Option α → Bool
   | some a => p a
   | none   => true
 
+/-- Checks that an optional value is not `none` and the value satisfies a predicate `p`. -/
 @[always_inline, inline] protected def any (p : α → Bool) : Option α → Bool
   | some a => p a
   | none   => false
 
+/--
+Implementation of `OrElse`'s `<|>` syntax for `Option`.
+-/
 @[always_inline, macro_inline] protected def orElse : Option α → (Unit → Option α) → Option α
   | some a, _ => some a
   | none,   b => b ()
@@ -81,10 +110,131 @@ def merge (fn : α → α → α) : Option α → Option α → Option α
   | none  , some y => some y
   | some x, some y => some <| fn x y
 
-end Option
+@[simp] theorem getD_none : getD none a = a := rfl
+@[simp] theorem getD_some : getD (some a) b = a := rfl
 
-deriving instance DecidableEq for Option
-deriving instance BEq for Option
+@[simp] theorem map_none' (f : α → β) : none.map f = none := rfl
+@[simp] theorem map_some' (a) (f : α → β) : (some a).map f = some (f a) := rfl
+
+@[simp] theorem none_bind (f : α → Option β) : none.bind f = none := rfl
+@[simp] theorem some_bind (a) (f : α → Option β) : (some a).bind f = f a := rfl
+
+
+/-- An elimination principle for `Option`. It is a nondependent version of `Option.recOn`. -/
+@[simp, inline] protected def elim : Option α → β → (α → β) → β
+  | some x, _, f => f x
+  | none, y, _ => y
+
+/-- Extracts the value `a` from an option that is known to be `some a` for some `a`. -/
+@[inline] def get {α : Type u} : (o : Option α) → isSome o → α
+  | some x, _ => x
+
+/-- `guard p a` returns `some a` if `p a` holds, otherwise `none`. -/
+@[inline] def guard (p : α → Prop) [DecidablePred p] (a : α) : Option α :=
+  if p a then some a else none
+
+/--
+Cast of `Option` to `List`. Returns `[a]` if the input is `some a`, and `[]` if it is `none`.
+-/
+@[inline] def toList : Option α → List α
+  | none => .nil
+  | some a => .cons a .nil
+
+/--
+Cast of `Option` to `Array`. Returns `#[a]` if the input is `some a`, and `#[]` if it is `none`.
+-/
+@[inline] def toArray : Option α → Array α
+  | none => List.toArray .nil
+  | some a => List.toArray (.cons a .nil)
+
+/--
+Two arguments failsafe function. Returns `f a b` if the inputs are `some a` and `some b`, and
+"does nothing" otherwise.
+-/
+def liftOrGet (f : α → α → α) : Option α → Option α → Option α
+  | none, none => none
+  | some a, none => some a
+  | none, some b => some b
+  | some a, some b => some (f a b)
+
+/-- Lifts a relation `α → β → Prop` to a relation `Option α → Option β → Prop` by just adding
+`none ~ none`. -/
+inductive Rel (r : α → β → Prop) : Option α → Option β → Prop
+  /-- If `a ~ b`, then `some a ~ some b` -/
+  | some {a b} : r a b → Rel r (some a) (some b)
+  /-- `none ~ none` -/
+  | none : Rel r none none
+
+/-- Flatten an `Option` of `Option`, a specialization of `joinM`. -/
+@[simp, inline] def join (x : Option (Option α)) : Option α := x.bind id
+
+/-- Like `Option.mapM` but for applicative functors. -/
+@[inline] protected def mapA [Applicative m] {α β} (f : α → m β) : Option α → m (Option β)
+  | none => pure none
+  | some x => some <$> f x
+
+/--
+If you maybe have a monadic computation in a `[Monad m]` which produces a term of type `α`, then
+there is a naturally associated way to always perform a computation in `m` which maybe produces a
+result.
+-/
+@[inline] def sequence [Monad m] {α : Type u} : Option (m α) → m (Option α)
+  | none => pure none
+  | some fn => some <$> fn
+
+/-- A monadic analogue of `Option.elim`. -/
+@[inline] def elimM [Monad m] (x : m (Option α)) (y : m β) (z : α → m β) : m β :=
+  do (← x).elim y z
+
+/-- A monadic analogue of `Option.getD`. -/
+@[inline] def getDM [Monad m] (x : Option α) (y : m α) : m α :=
+  match x with
+  | some a => pure a
+  | none => y
+
+instance (α) [BEq α] [LawfulBEq α] : LawfulBEq (Option α) where
+  rfl {x} :=
+    match x with
+    | some x => LawfulBEq.rfl (α := α)
+    | none => rfl
+  eq_of_beq {x y h} := by
+    match x, y with
+    | some x, some y => rw [LawfulBEq.eq_of_beq (α := α) h]
+    | none, none => rfl
+
+@[simp] theorem all_none : Option.all p none = true := rfl
+@[simp] theorem all_some : Option.all p (some x) = p x := rfl
+
+/-- The minimum of two optional values. -/
+protected def min [Min α] : Option α → Option α → Option α
+  | some x, some y => some (Min.min x y)
+  | some x, none => some x
+  | none, some y => some y
+  | none, none => none
+
+instance [Min α] : Min (Option α) where min := Option.min
+
+@[simp] theorem min_some_some [Min α] {a b : α} : min (some a) (some b) = some (min a b) := rfl
+@[simp] theorem min_some_none [Min α] {a : α} : min (some a) none = some a := rfl
+@[simp] theorem min_none_some [Min α] {b : α} : min none (some b) = some b := rfl
+@[simp] theorem min_none_none [Min α] : min (none : Option α) none = none := rfl
+
+/-- The maximum of two optional values. -/
+protected def max [Max α] : Option α → Option α → Option α
+  | some x, some y => some (Max.max x y)
+  | some x, none => some x
+  | none, some y => some y
+  | none, none => none
+
+instance [Max α] : Max (Option α) where max := Option.max
+
+@[simp] theorem max_some_some [Max α] {a b : α} : max (some a) (some b) = some (max a b) := rfl
+@[simp] theorem max_some_none [Max α] {a : α} : max (some a) none = some a := rfl
+@[simp] theorem max_none_some [Max α] {b : α} : max none (some b) = some b := rfl
+@[simp] theorem max_none_none [Max α] : max (none : Option α) none = none := rfl
+
+
+end Option
 
 instance [LT α] : LT (Option α) where
   lt := Option.lt (· < ·)