feat: lemmas about Option/if-then-else

Defines `mergeSort`, a naive stable merge sort algorithm, replaces it
via a `@[csimp]` lemma with something faster at runtime, and proves the
following results:

* `mergeSort_sorted`: `mergeSort` produces a sorted list.
* `mergeSort_perm`: `mergeSort` is a permutation of the input list.
* `mergeSort_of_sorted`: `mergeSort` does not change a sorted list.
* `mergeSort_cons`: proves `mergeSort le (x :: xs) = l₁ ++ x :: l₂` for
some `l₁, l₂`
so that `mergeSort le xs = l₁ ++ l₂`, and no `a ∈ l₁` satisfies `le a
x`.
* `mergeSort_stable`: if `c` is a sorted sublist of `l`, then `c` is
still a sublist of `mergeSort le l`.

.github/workflows/ci.yml

@@ -204,7 +204,7 @@ jobs:
                 "os": "macos-14",
                 "CMAKE_OPTIONS": "-DLEAN_INSTALL_SUFFIX=-darwin_aarch64",
                 "release": true,
-                "check-level": 1,
+                "check-level": 0,
                 "shell": "bash -euxo pipefail {0}",
                 "llvm-url": "https://github.com/leanprover/lean-llvm/releases/download/15.0.1/lean-llvm-aarch64-apple-darwin.tar.zst",
                 "prepare-llvm": "../script/prepare-llvm-macos.sh lean-llvm*",
@@ -226,21 +226,19 @@ jobs:
               },
               {
                 "name": "Linux aarch64",
-                "os": "ubuntu-latest",
+                "os": "nscloud-ubuntu-22.04-arm64-4x8",
                 "CMAKE_OPTIONS": "-DUSE_GMP=OFF -DLEAN_INSTALL_SUFFIX=-linux_aarch64",
                 "release": true,
                 "check-level": 2,
-                "cross": true,
-                "cross_target": "aarch64-unknown-linux-gnu",
                 "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-*"
+                "llvm-url": "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*"
               },
               {
                 "name": "Linux 32bit",
                 "os": "ubuntu-latest",
                 // Use 32bit on stage0 and stage1 to keep oleans compatible
-                "CMAKE_OPTIONS": "-DSTAGE0_USE_GMP=OFF -DSTAGE0_LEAN_EXTRA_CXX_FLAGS='-m32' -DSTAGE0_LEANC_OPTS='-m32' -DSTAGE0_MMAP=OFF -DUSE_GMP=OFF -DLEAN_EXTRA_CXX_FLAGS='-m32' -DLEANC_OPTS='-m32' -DMMAP=OFF -DLEAN_INSTALL_SUFFIX=-linux_x86",
+                "CMAKE_OPTIONS": "-DSTAGE0_USE_GMP=OFF -DSTAGE0_LEAN_EXTRA_CXX_FLAGS='-m32' -DSTAGE0_LEANC_OPTS='-m32' -DSTAGE0_MMAP=OFF -DUSE_GMP=OFF -DLEAN_EXTRA_CXX_FLAGS='-m32' -DLEANC_OPTS='-m32' -DMMAP=OFF -DLEAN_INSTALL_SUFFIX=-linux_x86 -DCMAKE_LIBRARY_PATH=/usr/lib/i386-linux-gnu/ -DSTAGE0_CMAKE_LIBRARY_PATH=/usr/lib/i386-linux-gnu/",
                 "cmultilib": true,
                 "release": true,
                 "check-level": 2,
@@ -251,7 +249,7 @@ jobs:
                 "name": "Web Assembly",
                 "os": "ubuntu-latest",
                 // Build a native 32bit binary in stage0 and use it to compile the oleans and the wasm build
-                "CMAKE_OPTIONS": "-DCMAKE_C_COMPILER_WORKS=1 -DSTAGE0_USE_GMP=OFF -DSTAGE0_LEAN_EXTRA_CXX_FLAGS='-m32' -DSTAGE0_LEANC_OPTS='-m32' -DSTAGE0_CMAKE_CXX_COMPILER=clang++ -DSTAGE0_CMAKE_C_COMPILER=clang -DSTAGE0_CMAKE_EXECUTABLE_SUFFIX=\"\" -DUSE_GMP=OFF -DMMAP=OFF -DSTAGE0_MMAP=OFF -DCMAKE_AR=../emsdk/emsdk-main/upstream/emscripten/emar -DCMAKE_TOOLCHAIN_FILE=../emsdk/emsdk-main/upstream/emscripten/cmake/Modules/Platform/Emscripten.cmake -DLEAN_INSTALL_SUFFIX=-linux_wasm32",
+                "CMAKE_OPTIONS": "-DCMAKE_C_COMPILER_WORKS=1 -DSTAGE0_USE_GMP=OFF -DSTAGE0_LEAN_EXTRA_CXX_FLAGS='-m32' -DSTAGE0_LEANC_OPTS='-m32' -DSTAGE0_CMAKE_CXX_COMPILER=clang++ -DSTAGE0_CMAKE_C_COMPILER=clang -DSTAGE0_CMAKE_EXECUTABLE_SUFFIX=\"\" -DUSE_GMP=OFF -DMMAP=OFF -DSTAGE0_MMAP=OFF -DCMAKE_AR=../emsdk/emsdk-main/upstream/emscripten/emar -DCMAKE_TOOLCHAIN_FILE=../emsdk/emsdk-main/upstream/emscripten/cmake/Modules/Platform/Emscripten.cmake -DLEAN_INSTALL_SUFFIX=-linux_wasm32 -DSTAGE0_CMAKE_LIBRARY_PATH=/usr/lib/i386-linux-gnu/",
                 "wasm": true,
                 "cmultilib": true,
                 "release": true,
@@ -259,7 +257,7 @@ jobs:
                 "cross": true,
                 "shell": "bash -euxo pipefail {0}",
                 // Just a few selected tests because wasm is slow
-                "CTEST_OPTIONS": "-R \"leantest_1007\\.lean|leantest_Format\\.lean|leanruntest\\_1037.lean|leanruntest_ac_rfl\\.lean\""
+                "CTEST_OPTIONS": "-R \"leantest_1007\\.lean|leantest_Format\\.lean|leanruntest\\_1037.lean|leanruntest_ac_rfl\\.lean|leanruntest_libuv\\.lean\""
               }
             ];
             console.log(`matrix:\n${JSON.stringify(matrix, null, 2)}`)
@@ -298,12 +296,12 @@ jobs:
         uses: msys2/setup-msys2@v2
         with:
           msystem: clang64
-          # `:p` means prefix with appropriate msystem prefix
-          pacboy: "make python cmake:p clang:p ccache:p gmp:p git zip unzip diffutils binutils tree zstd:p tar"
+          # `:` means do not prefix with msystem
+          pacboy: "make: python: cmake clang ccache gmp libuv git: zip: unzip: diffutils: binutils: tree: zstd tar:"
         if: runner.os == 'Windows'
       - name: Install Brew Packages
         run: |
-          brew install ccache tree zstd coreutils gmp
+          brew install ccache tree zstd coreutils gmp libuv
         if: runner.os == 'macOS'
       - name: Checkout
         uses: actions/checkout@v4
@@ -327,17 +325,19 @@ jobs:
         if: matrix.wasm
       - name: Install 32bit c libs
         run: |
+          sudo dpkg --add-architecture i386
           sudo apt-get update
-          sudo apt-get install -y gcc-multilib g++-multilib ccache
+          sudo apt-get install -y gcc-multilib g++-multilib ccache libuv1-dev:i386
         if: matrix.cmultilib
       - name: Cache
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: .ccache
           key: ${{ matrix.name }}-build-v3-${{ github.event.pull_request.head.sha }}
           # fall back to (latest) previous cache
           restore-keys: |
             ${{ matrix.name }}-build-v3
+          save-always: true
       # open nix-shell once for initial setup
       - name: Setup
         run: |
@@ -382,6 +382,12 @@ jobs:
           make -C build install
       - name: Check Binaries
         run: ${{ matrix.binary-check }} lean-*/bin/* || true
+      - name: Count binary symbols
+        run: |
+          for f in lean-*/bin/*; do
+            echo "$f: $(nm $f | grep " T " | wc -l) exported symbols"
+          done
+        if: matrix.name == 'Windows'
       - name: List Install Tree
         run: |
           # omit contents of Init/, ...
@@ -426,7 +432,7 @@ jobs:
         if: matrix.test-speedcenter
       - name: Check Stage 3
         run: |
-          make -C build -j$NPROC stage3
+          make -C build -j$NPROC check-stage3
         if: matrix.test-speedcenter
       - name: Test Speedcenter Benchmarks
         run: |
@@ -455,12 +461,24 @@ jobs:
     # mark as merely cancelled not failed if builds are cancelled
     if: ${{ !cancelled() }}
     steps:
+    - if: ${{ contains(needs.*.result, 'failure') && github.repository == 'leanprover/lean4' && github.ref_name == 'master' }}
+      uses: zulip/github-actions-zulip/send-message@v1
+      with:
+        api-key: ${{ secrets.ZULIP_BOT_KEY }}
+        email: "github-actions-bot@lean-fro.zulipchat.com"
+        organization-url: "https://lean-fro.zulipchat.com"
+        to: "infrastructure"
+        topic: "Github actions"
+        type: "stream"
+        content: |
+          A build of `${{ github.ref_name }}`, triggered by event `${{ github.event_name }}`, [failed](https://github.com/${{ github.repository }}/actions/runs/${{ github.run_id }}).
     - if: contains(needs.*.result, 'failure')
       uses: actions/github-script@v7
       with:
         script: |
             core.setFailed('Some jobs failed')
 
+
   # This job creates releases from tags
   # (whether they are "unofficial" releases for experiments, or official releases when the tag is "v" followed by a semver string.)
   # We do not attempt to automatically construct a changelog here:
@@ -533,3 +551,8 @@ jobs:
           gh workflow -R leanprover/release-index run update-index.yml
         env:
           GITHUB_TOKEN: ${{ secrets.RELEASE_INDEX_TOKEN }}
+      - name: Update toolchain on mathlib4's nightly-testing branch
+        run: |
+          gh workflow -R leanprover-community/mathlib4 run nightly_bump_toolchain.yml
+        env:
+          GITHUB_TOKEN: ${{ secrets.MATHLIB4_BOT }}

.github/workflows/jira.yml

@@ -0,0 +1,34 @@
+name: Jira sync
+
+on:
+  issues:
+    types: [closed]
+
+jobs:
+  jira-sync:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Move Jira issue to Done
+        env:
+          JIRA_API_TOKEN: ${{ secrets.JIRA_API_TOKEN }}
+          JIRA_USERNAME: ${{ secrets.JIRA_USERNAME }}
+          JIRA_BASE_URL: ${{ secrets.JIRA_BASE_URL }}
+        run: |
+          issue_number=${{ github.event.issue.number }}
+
+          jira_issue_key=$(curl -s -u "${JIRA_USERNAME}:${JIRA_API_TOKEN}" \
+            -X GET -H "Content-Type: application/json" \
+            "${JIRA_BASE_URL}/rest/api/2/search?jql=summary~\"${issue_number}\"" | \
+            jq -r '.issues[0].key')
+
+          if [ -z "$jira_issue_key" ]; then
+            exit
+          fi
+
+          curl -s -u "${JIRA_USERNAME}:${JIRA_API_TOKEN}" \
+            -X POST -H "Content-Type: application/json" \
+            --data "{\"transition\": {\"id\": \"41\"}}" \
+            "${JIRA_BASE_URL}/rest/api/2/issue/${jira_issue_key}/transitions"
+
+          echo "Moved Jira issue ${jira_issue_key} to Done"

.github/workflows/nix-ci.yml

@@ -55,13 +55,14 @@ jobs:
           # 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 }}
       - name: Set Up Nix Cache
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: nix-store-cache
           key: ${{ matrix.name }}-nix-store-cache-${{ github.sha }}
           # fall back to (latest) previous cache
           restore-keys: |
             ${{ matrix.name }}-nix-store-cache
+          save-always: true
       - name: Further Set Up Nix Cache
         shell: bash -euxo pipefail {0}
         run: |
@@ -78,13 +79,14 @@ jobs:
           sudo mkdir -m0770 -p /nix/var/cache/ccache
           sudo chown -R $USER /nix/var/cache/ccache
       - name: Setup CCache Cache
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: /nix/var/cache/ccache
           key: ${{ matrix.name }}-nix-ccache-${{ github.sha }}
           # fall back to (latest) previous cache
           restore-keys: |
             ${{ matrix.name }}-nix-ccache
+          save-always: true
       - name: Further Set Up CCache Cache
         run: |
           sudo chown -R root:nixbld /nix/var/cache
@@ -103,7 +105,7 @@ jobs:
         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
+          nix build $NIX_BUILD_ARGS --update-input lean --no-write-lock-file ./doc#{lean-mdbook,leanInk,alectryon,inked} -o push-doc
           nix build $NIX_BUILD_ARGS --update-input lean --no-write-lock-file ./doc
           # https://github.com/netlify/cli/issues/1809
           cp -r --dereference ./result ./dist
@@ -146,5 +148,3 @@ jobs:
       - name: Fixup CCache Cache
         run: |
           sudo chown -R $USER /nix/var/cache
-      - name: CCache stats
-        run: CCACHE_DIR=/nix/var/cache/ccache nix run .#nixpkgs.ccache -- -s

.github/workflows/pr-release.yml

@@ -163,7 +163,8 @@ jobs:
             # so keep in sync
 
             # Use GitHub API to check if a comment already exists
-            existing_comment="$(curl -L -s -H "Authorization: token ${{ secrets.MATHLIB4_BOT }}" \
+            existing_comment="$(curl --retry 3 --location --silent \
+                                    -H "Authorization: token ${{ secrets.MATHLIB4_BOT }}" \
                                     -H "Accept: application/vnd.github.v3+json" \
                                     "https://api.github.com/repos/leanprover/lean4/issues/${{ steps.workflow-info.outputs.pullRequestNumber }}/comments" \
                                     | jq 'first(.[] | select(.body | test("^- . Mathlib") or startswith("Mathlib CI status")) | select(.user.login == "leanprover-community-mathlib4-bot"))')"
@@ -328,7 +329,7 @@ jobs:
             git switch -c lean-pr-testing-${{ steps.workflow-info.outputs.pullRequestNumber }} "$BASE"
             echo "leanprover/lean4-pr-releases:pr-release-${{ steps.workflow-info.outputs.pullRequestNumber }}" > lean-toolchain
             git add lean-toolchain
-            sed -i 's,require "leanprover-community" / "batteries" @ ".\+",require "leanprover-community" / "batteries" @ "git#nightly-testing-'"${MOST_RECENT_NIGHTLY}"'",' lakefile.lean
+            sed -i 's,require "leanprover-community" / "batteries" @ git ".\+",require "leanprover-community" / "batteries" @ git "nightly-testing-'"${MOST_RECENT_NIGHTLY}"'",' lakefile.lean
             lake update batteries
             git add lakefile.lean lake-manifest.json
             git commit -m "Update lean-toolchain for testing https://github.com/leanprover/lean4/pull/${{ steps.workflow-info.outputs.pullRequestNumber }}"

.github/workflows/update-stage0.yml

@@ -47,7 +47,7 @@ jobs:
     #  uses: DeterminateSystems/magic-nix-cache-action@v2
     - if: env.should_update_stage0 == 'yes'
       name: Restore Build Cache
-      uses: actions/cache/restore@v3
+      uses: actions/cache/restore@v4
       with:
         path: nix-store-cache
         key: Nix Linux-nix-store-cache-${{ github.sha }}

CONTRIBUTING.md

@@ -63,6 +63,20 @@ Because the change will be squashed, there is no need to polish the commit messa
 Reviews and Feedback:
 ----
 
+The lean4 repo is managed by the Lean FRO's *triage team* that aims to provide initial feedback on new bug reports, PRs, and RFCs weekly.
+This feedback generally consists of prioritizing the ticket using one of the following categories:
+* label `P-high`: We will work on this issue
+* label `P-medium`: We may work on this issue if we find the time
+* label `P-low`: We are not planning to work on this issue
+* *closed*: This issue is already fixed, it is not an issue, or is not sufficiently compatible with our roadmap for the project and we will not work on it nor accept external contributions on it
+
+For *bug reports*, the listed priority reflects our commitment to fixing the issue.
+It is generally indicative but not necessarily identical to the priority an external contribution addressing this bug would receive.
+For *PRs* and *RFCs*, the priority reflects our commitment to reviewing them and getting them to an acceptable state.
+Accepted RFCs are marked with the label `RFC accepted` and afterwards assigned a new "implementation" priority as with bug reports.
+
+General guidelines for interacting with reviews and feedback:
+
 **Be Patient**: Given the limited number of full-time maintainers and the volume of PRs, reviews may take some time.
 
 **Engage Constructively**: Always approach feedback positively and constructively. Remember, reviews are about ensuring the best quality for the project, not personal criticism.

RELEASES.md

@@ -8,16 +8,299 @@ 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.
 
-v4.11.0
+v4.12.0
 ----------
 Development in progress.
 
+v4.11.0
+----------
+Release candidate, release notes will be copied from the branch `releases/v4.11.0` once completed.
+
 v4.10.0
 ----------
-Release candidate, release notes will be copied from branch `releases/v4.10.0` once completed.
+
+### Language features, tactics, and metaprograms
+
+* `split` tactic:
+  * [#4401](https://github.com/leanprover/lean4/pull/4401) improves the strategy `split` uses to generalize discriminants of matches and adds `trace.split.failure` trace class for diagnosing issues.
+
+* `rw` tactic:
+  * [#4385](https://github.com/leanprover/lean4/pull/4385) prevents the tactic from claiming pre-existing goals are new subgoals.
+  * [dac1da](https://github.com/leanprover/lean4/commit/dac1dacc5b39911827af68247d575569d9c399b5) adds configuration for ordering new goals, like for `apply`.
+
+* `simp` tactic:
+  * [#4430](https://github.com/leanprover/lean4/pull/4430) adds `dsimproc`s for `if` expressions (`ite` and `dite`).
+  * [#4434](https://github.com/leanprover/lean4/pull/4434) improves heuristics for unfolding. Equational lemmas now have priorities where more-specific equationals lemmas are tried first before a possible catch-all.
+  * [#4481](https://github.com/leanprover/lean4/pull/4481) fixes an issue where function-valued `OfNat` numeric literals would become denormalized.
+  * [#4467](https://github.com/leanprover/lean4/pull/4467) fixes an issue where dsimp theorems might not apply to literals.
+  * [#4484](https://github.com/leanprover/lean4/pull/4484) fixes the source position for the warning for deprecated simp arguments.
+  * [#4258](https://github.com/leanprover/lean4/pull/4258) adds docstrings for `dsimp` configuration.
+  * [#4567](https://github.com/leanprover/lean4/pull/4567) improves the accuracy of used simp lemmas reported by `simp?`.
+  * [fb9727](https://github.com/leanprover/lean4/commit/fb97275dcbb683efe6da87ed10a3f0cd064b88fd) adds (but does not implement) the simp configuration option `implicitDefEqProofs`, which will enable including `rfl`-theorems in proof terms.
+* `omega` tactic:
+  * [#4360](https://github.com/leanprover/lean4/pull/4360) makes the tactic generate error messages lazily, improving its performance when used in tactic combinators.
+* `bv_omega` tactic:
+  * [#4579](https://github.com/leanprover/lean4/pull/4579) works around changes to the definition of `Fin.sub` in this release.
+* [#4490](https://github.com/leanprover/lean4/pull/4490) sets up groundwork for a tactic index in generated documentation, as there was in Lean 3. See PR description for details.
+
+* **Commands**
+  * [#4370](https://github.com/leanprover/lean4/pull/4370) makes the `variable` command fully elaborate binders during validation, fixing an issue where some errors would be reported only at the next declaration.
+  * [#4408](https://github.com/leanprover/lean4/pull/4408) fixes a discrepency in universe parameter order between `theorem` and `def` declarations.
+  * [#4493](https://github.com/leanprover/lean4/pull/4493) and
+    [#4482](https://github.com/leanprover/lean4/pull/4482) fix a discrepancy in the elaborators for `theorem`, `def`, and `example`,
+    making `Prop`-valued `example`s and other definition commands elaborate like `theorem`s.
+  * [8f023b](https://github.com/leanprover/lean4/commit/8f023b85c554186ae562774b8122322d856c674e), [3c4d6b](https://github.com/leanprover/lean4/commit/3c4d6ba8648eb04d90371eb3fdbd114d16949501) and [0783d0](https://github.com/leanprover/lean4/commit/0783d0fcbe31b626fbd3ed2f29d838e717f09101) change the `#reduce` command to be able to control what gets reduced.
+    For example, `#reduce (proofs := true) (types := false) e` reduces both proofs and types in the expression `e`.
+    By default, neither proofs or types are reduced.
+  * [#4489](https://github.com/leanprover/lean4/pull/4489) fixes an elaboration bug in `#check_tactic`.
+  * [#4505](https://github.com/leanprover/lean4/pull/4505) adds support for `open _root_.<namespace>`.
+
+* **Options**
+  * [#4576](https://github.com/leanprover/lean4/pull/4576) adds the `debug.byAsSorry` option. Setting `set_option debug.byAsSorry true` causes all `by ...` terms to elaborate as `sorry`.
+  * [7b56eb](https://github.com/leanprover/lean4/commit/7b56eb20a03250472f4b145118ae885274d1f8f7) and [d8e719](https://github.com/leanprover/lean4/commit/d8e719f9ab7d049e423473dfc7a32867d32c856f) add the `debug.skipKernelTC` option. Setting `set_option debug.skipKernelTC true` turns off kernel typechecking. This is meant for temporarily working around kernel performance issues, and it compromises soundness since buggy tactics may produce invalid proofs, which will not be caught if this option is set to true.
+
+* [#4301](https://github.com/leanprover/lean4/pull/4301)
+  adds a linter to flag situations where a local variable's name is one of
+  the argumentless constructors of its type. This can arise when a user either
+  doesn't open a namespace or doesn't add a dot or leading qualifier, as
+  in the following:
+
+  ```lean
+  inductive Tree (α : Type) where
+    | leaf
+    | branch (left : Tree α) (val : α) (right : Tree α)
+
+  def depth : Tree α → Nat
+    | leaf => 0
+  ```
+
+  With this linter, the `leaf` pattern is highlighted as a local
+  variable whose name overlaps with the constructor `Tree.leaf`.
+
+  The linter can be disabled with `set_option linter.constructorNameAsVariable false`.
+
+  Additionally, the error message that occurs when a name in a pattern that takes arguments isn't valid now suggests similar names that would be valid. This means that the following definition:
+
+  ```lean
+  def length (list : List α) : Nat :=
+    match list with
+    | nil => 0
+    | cons x xs => length xs + 1
+  ```
+
+  now results in the following warning:
+
+  ```
+  warning: Local variable 'nil' resembles constructor 'List.nil' - write '.nil' (with a dot) or 'List.nil' to use the constructor.
+  note: this linter can be disabled with `set_option linter.constructorNameAsVariable false`
+  ```
+
+  and error:
+
+  ```
+  invalid pattern, constructor or constant marked with '[match_pattern]' expected
+
+  Suggestion: 'List.cons' is similar
+  ```
+
+* **Metaprogramming**
+  * [#4454](https://github.com/leanprover/lean4/pull/4454) adds public `Name.isInternalDetail` function for filtering declarations using naming conventions for internal names.
+
+* **Other fixes or improvements**
+  * [#4416](https://github.com/leanprover/lean4/pull/4416) sorts the ouput of `#print axioms` for determinism.
+  * [#4528](https://github.com/leanprover/lean4/pull/4528) fixes error message range for the cdot focusing tactic.
+
+### Language server, widgets, and IDE extensions
+
+* [#4443](https://github.com/leanprover/lean4/pull/4443) makes the watchdog be more resilient against badly behaving clients.
+
+### Pretty printing
+
+* [#4433](https://github.com/leanprover/lean4/pull/4433) restores fallback pretty printers when context is not available, and documents `addMessageContext`.
+* [#4556](https://github.com/leanprover/lean4/pull/4556) introduces `pp.maxSteps` option and sets the default value of `pp.deepTerms` to `false`. Together, these keep excessively large or deep terms from overwhelming the Infoview.
+
+### Library
+* [#4560](https://github.com/leanprover/lean4/pull/4560) splits `GetElem` class into `GetElem` and `GetElem?`.
+  This enables removing `Decidable` instance arguments from `GetElem.getElem?` and `GetElem.getElem!`, improving their rewritability.
+  See the docstrings for these classes for more information.
+* `Array`
+  * [#4389](https://github.com/leanprover/lean4/pull/4389) makes `Array.toArrayAux_eq` be a `simp` lemma.
+  * [#4399](https://github.com/leanprover/lean4/pull/4399) improves robustness of the proof for `Array.reverse_data`.
+* `List`
+  * [#4469](https://github.com/leanprover/lean4/pull/4469) and [#4475](https://github.com/leanprover/lean4/pull/4475) improve the organization of the `List` API.
+  * [#4470](https://github.com/leanprover/lean4/pull/4470) improves the `List.set` and `List.concat` API.
+  * [#4472](https://github.com/leanprover/lean4/pull/4472) upstreams lemmas about `List.filter` from Batteries.
+  * [#4473](https://github.com/leanprover/lean4/pull/4473) adjusts `@[simp]` attributes.
+  * [#4488](https://github.com/leanprover/lean4/pull/4488) makes `List.getElem?_eq_getElem` be a simp lemma.
+  * [#4487](https://github.com/leanprover/lean4/pull/4487) adds missing `List.replicate` API.
+  * [#4521](https://github.com/leanprover/lean4/pull/4521) adds lemmas about `List.map`.
+  * [#4500](https://github.com/leanprover/lean4/pull/4500) changes `List.length_cons` to use `as.length + 1` instead of `as.length.succ`.
+  * [#4524](https://github.com/leanprover/lean4/pull/4524) fixes the statement of `List.filter_congr`.
+  * [#4525](https://github.com/leanprover/lean4/pull/4525) changes binder explicitness in `List.bind_map`.
+  * [#4550](https://github.com/leanprover/lean4/pull/4550) adds `maximum?_eq_some_iff'` and `minimum?_eq_some_iff?`.
+* [#4400](https://github.com/leanprover/lean4/pull/4400) switches the normal forms for indexing `List` and `Array` to `xs[n]` and `xs[n]?`.
+* `HashMap`
+  * [#4372](https://github.com/leanprover/lean4/pull/4372) fixes linearity in `HashMap.insert` and `HashMap.erase`, leading to a 40% speedup in a replace-heavy workload.
+* `Option`
+  * [#4403](https://github.com/leanprover/lean4/pull/4403) generalizes type of `Option.forM` from `Unit` to `PUnit`.
+  * [#4504](https://github.com/leanprover/lean4/pull/4504) remove simp attribute from `Option.elim` and instead adds it to individal reduction lemmas, making unfolding less aggressive.
+* `Nat`
+  * [#4242](https://github.com/leanprover/lean4/pull/4242) adds missing theorems for `n + 1` and `n - 1` normal forms.
+  * [#4486](https://github.com/leanprover/lean4/pull/4486) makes `Nat.min_assoc` be a simp lemma.
+  * [#4522](https://github.com/leanprover/lean4/pull/4522) moves `@[simp]` from `Nat.pred_le` to `Nat.sub_one_le`.
+  * [#4532](https://github.com/leanprover/lean4/pull/4532) changes various `Nat.succ n` to `n + 1`.
+* `Int`
+  * [#3850](https://github.com/leanprover/lean4/pull/3850) adds complete div/mod simprocs for `Int`.
+* `String`/`Char`
+  * [#4357](https://github.com/leanprover/lean4/pull/4357) make the byte size interface be `Nat`-valued with functions `Char.utf8Size` and `String.utf8ByteSize`.
+  * [#4438](https://github.com/leanprover/lean4/pull/4438) upstreams `Char.ext` from Batteries and adds some `Char` documentation to the manual.
+* `Fin`
+  * [#4421](https://github.com/leanprover/lean4/pull/4421) adjusts `Fin.sub` to be more performant in definitional equality checks.
+* `Prod`
+  * [#4526](https://github.com/leanprover/lean4/pull/4526) adds missing `Prod.map` lemmas.
+  * [#4533](https://github.com/leanprover/lean4/pull/4533) fixes binder explicitness in lemmas.
+* `BitVec`
+  * [#4428](https://github.com/leanprover/lean4/pull/4428) adds missing `simproc` for `BitVec` equality.
+  * [#4417](https://github.com/leanprover/lean4/pull/4417) adds `BitVec.twoPow` and lemmas, toward bitblasting multiplication for LeanSAT.
+* `Std` library
+  * [#4499](https://github.com/leanprover/lean4/pull/4499) introduces `Std`, a library situated between `Init` and `Lean`, providing functionality not in the prelude both to Lean's implementation and to external users.
+* **Other fixes or improvements**
+  * [#3056](https://github.com/leanprover/lean4/pull/3056) standardizes on using `(· == a)` over `(a == ·)`.
+  * [#4502](https://github.com/leanprover/lean4/pull/4502) fixes errors reported by running the library through the the Batteries linters.
+
+### Lean internals
+
+* [#4391](https://github.com/leanprover/lean4/pull/4391) makes `getBitVecValue?` recognize `BitVec.ofNatLt`.
+* [#4410](https://github.com/leanprover/lean4/pull/4410) adjusts `instantiateMVars` algorithm to zeta reduce `let` expressions while beta reducing instantiated metavariables.
+* [#4420](https://github.com/leanprover/lean4/pull/4420) fixes occurs check for metavariable assignments to also take metavariable types into account.
+* [#4425](https://github.com/leanprover/lean4/pull/4425) fixes `forEachModuleInDir` to iterate over each Lean file exactly once.
+* [#3886](https://github.com/leanprover/lean4/pull/3886) adds support to build Lean core oleans using Lake.
+* **Defeq and WHNF algorithms**
+  * [#4387](https://github.com/leanprover/lean4/pull/4387) improves performance of `isDefEq` by eta reducing lambda-abstracted terms during metavariable assignments, since these are beta reduced during metavariable instantiation anyway.
+  * [#4388](https://github.com/leanprover/lean4/pull/4388) removes redundant code in `isDefEqQuickOther`.
+* **Typeclass inference**
+  * [#4530](https://github.com/leanprover/lean4/pull/4530) fixes handling of metavariables when caching results at `synthInstance?`.
+* **Elaboration**
+  * [#4426](https://github.com/leanprover/lean4/pull/4426) makes feature where the "don't know how to synthesize implicit argument" error reports the name of the argument more reliable.
+  * [#4497](https://github.com/leanprover/lean4/pull/4497) fixes a name resolution bug for generalized field notation (dot notation).
+  * [#4536](https://github.com/leanprover/lean4/pull/4536) blocks the implicit lambda feature for `(e :)` notation.
+  * [#4562](https://github.com/leanprover/lean4/pull/4562) makes it be an error for there to be two functions with the same name in a `where`/`let rec` block.
+* Recursion principles
+  * [#4549](https://github.com/leanprover/lean4/pull/4549) refactors `findRecArg`, extracting `withRecArgInfo`.
+    Errors are now reported in parameter order rather than the order they are tried (non-indices are tried first).
+    For every argument, it will say why it wasn't tried, even if the reason is obvious (e.g. a fixed prefix or is `Prop`-typed, etc.).
+* Porting core C++ to Lean
+  * [#4474](https://github.com/leanprover/lean4/pull/4474) takes a step to refactor `constructions` toward a future port to Lean.
+  * [#4498](https://github.com/leanprover/lean4/pull/4498) ports `mk_definition_inferring_unsafe` to Lean.
+  * [#4516](https://github.com/leanprover/lean4/pull/4516) ports `recOn` construction to Lean.
+  * [#4517](https://github.com/leanprover/lean4/pull/4517), [#4653](https://github.com/leanprover/lean4/pull/4653), and [#4651](https://github.com/leanprover/lean4/pull/4651) port `below` and `brecOn` construction to Lean.
+* Documentation
+  * [#4501](https://github.com/leanprover/lean4/pull/4501) adds a more-detailed docstring for `PersistentEnvExtension`.
+* **Other fixes or improvements**
+  * [#4382](https://github.com/leanprover/lean4/pull/4382) removes `@[inline]` attribute from `NameMap.find?`, which caused respecialization at each call site.
+  * [5f9ded](https://github.com/leanprover/lean4/commit/5f9dedfe5ee9972acdebd669f228f487844a6156) improves output of `trace.Elab.snapshotTree`.
+  * [#4424](https://github.com/leanprover/lean4/pull/4424) removes "you might need to open '{dir}' in your editor" message that is now handled by Lake and the VS Code extension.
+  * [#4451](https://github.com/leanprover/lean4/pull/4451) improves the performance of `CollectMVars` and `FindMVar`.
+  * [#4479](https://github.com/leanprover/lean4/pull/4479) adds missing `DecidableEq` and `Repr` instances for intermediate structures used by the `BitVec` and `Fin` simprocs.
+  * [#4492](https://github.com/leanprover/lean4/pull/4492) adds tests for a previous `isDefEq` issue.
+  * [9096d6](https://github.com/leanprover/lean4/commit/9096d6fc7180fe533c504f662bcb61550e4a2492) removes `PersistentHashMap.size`.
+  * [#4508](https://github.com/leanprover/lean4/pull/4508) fixes `@[implemented_by]` for functions defined by well-founded recursion.
+  * [#4509](https://github.com/leanprover/lean4/pull/4509) adds additional tests for `apply?` tactic.
+  * [d6eab3](https://github.com/leanprover/lean4/commit/d6eab393f4df9d473b5736d636b178eb26d197e6) fixes a benchmark.
+  * [#4563](https://github.com/leanprover/lean4/pull/4563) adds a workaround for a bug in `IndPredBelow.mkBelowMatcher`.
+* **Cleanup:** [#4380](https://github.com/leanprover/lean4/pull/4380), [#4431](https://github.com/leanprover/lean4/pull/4431), [#4494](https://github.com/leanprover/lean4/pull/4494), [e8f768](https://github.com/leanprover/lean4/commit/e8f768f9fd8cefc758533bc76e3a12b398ed4a39), [de2690](https://github.com/leanprover/lean4/commit/de269060d17a581ed87f40378dbec74032633b27), [d3a756](https://github.com/leanprover/lean4/commit/d3a7569c97123d022828106468d54e9224ed8207), [#4404](https://github.com/leanprover/lean4/pull/4404), [#4537](https://github.com/leanprover/lean4/pull/4537).
+
+### Compiler, runtime, and FFI
+
+* [d85d3d](https://github.com/leanprover/lean4/commit/d85d3d5f3a09ff95b2ee47c6f89ef50b7e339126) fixes criterion for tail-calls in ownership calculation.
+* [#3963](https://github.com/leanprover/lean4/pull/3963) adds validation of UTF-8 at the C++-to-Lean boundary in the runtime.
+* [#4512](https://github.com/leanprover/lean4/pull/4512) fixes missing unboxing in interpreter when loading initialized value.
+* [#4477](https://github.com/leanprover/lean4/pull/4477) exposes the compiler flags for the bundled C compiler (clang).
+
+### Lake
+
+* [#4384](https://github.com/leanprover/lean4/pull/4384) deprecates `inputFile` and replaces it with `inputBinFile` and `inputTextFile`. Unlike `inputBinFile` (and `inputFile`), `inputTextFile` normalizes line endings, which helps ensure text file traces are platform-independent.
+* [#4371](https://github.com/leanprover/lean4/pull/4371) simplifies dependency resolution code.
+* [#4439](https://github.com/leanprover/lean4/pull/4439) touches up the Lake configuration DSL and makes other improvements:
+  string literals can now be used instead of identifiers for names,
+  avoids using French quotes in `lake new` and `lake init` templates,
+  changes the `exe` template to use `Main` for the main module,
+  improves the `math` template error if `lean-toolchain` fails to download,
+  and downgrades unknown configuration fields from an error to a warning to improve cross-version compatibility.
+* [#4496](https://github.com/leanprover/lean4/pull/4496) tweaks `require` syntax and updates docs. Now `require` in TOML for a package name such as `doc-gen4` does not need French quotes.
+* [#4485](https://github.com/leanprover/lean4/pull/4485) fixes a bug where package versions in indirect dependencies would take precedence over direct dependencies.
+* [#4478](https://github.com/leanprover/lean4/pull/4478) fixes a bug where Lake incorrectly included the module dynamic library in a platform-independent trace.
+* [#4529](https://github.com/leanprover/lean4/pull/4529) fixes some issues with bad import errors.
+  A bad import in an executable no longer prevents the executable's root
+  module from being built. This also fixes a problem where the location
+  of a transitive bad import would not been shown.
+  The root module of the executable now respects `nativeFacets`.
+* [#4564](https://github.com/leanprover/lean4/pull/4564) fixes a bug where non-identifier script names could not be entered on the CLI without French quotes.
+* [#4566](https://github.com/leanprover/lean4/pull/4566) addresses a few issues with precompiled libraries.
+  * Fixes a bug where Lake would always precompile the package of a module.
+  * If a module is precompiled, it now precompiles its imports. Previously, it would only do this if imported.
+* [#4495](https://github.com/leanprover/lean4/pull/4495), [#4692](https://github.com/leanprover/lean4/pull/4692), [#4849](https://github.com/leanprover/lean4/pull/4849)
+  add a new type of `require` that fetches package metadata from a
+  registry API endpoint (e.g. Reservoir) and then clones a Git package
+  using the information provided. To require such a dependency, the new
+  syntax is:
+
+  ```lean
+  require <scope> / <pkg-name> [@ git <rev>]
+  -- Examples:
+  require "leanprover" / "doc-gen4"
+  require "leanprover-community" / "proofwidgets" @ git "v0.0.39"
+  ```
+
+  Or in TOML:
+  ```toml
+  [[require]]
+  name = "<pkg-name>"
+  scope = "<scope>"
+  rev = "<rev>"
+  ```
+
+  Unlike with Git dependencies, Lake can make use of the richer
+  information provided by the registry to determine the default branch of
+  the package. This means for repositories of packages like `doc-gen4`
+  which have a default branch that is not `master`, Lake will now use said
+  default branch (e.g., in `doc-gen4`'s case, `main`).
+
+  Lake also supports configuring the registry endpoint via an environment
+  variable: `RESERVIOR_API_URL`. Thus, any server providing a similar
+  interface to Reservoir can be used as the registry. Further
+  configuration options paralleling those of Cargo's [Alternative Registries](https://doc.rust-lang.org/cargo/reference/registries.html)
+  and [Source Replacement](https://doc.rust-lang.org/cargo/reference/source-replacement.html)
+  will come in the future.
+
+### DevOps/CI
+* [#4427](https://github.com/leanprover/lean4/pull/4427) uses Namespace runners for CI for `leanprover/lean4`.
+* [#4440](https://github.com/leanprover/lean4/pull/4440) fixes speedcenter tests in CI.
+* [#4441](https://github.com/leanprover/lean4/pull/4441) fixes that workflow change would break CI for unrebased PRs.
+* [#4442](https://github.com/leanprover/lean4/pull/4442) fixes Wasm release-ci.
+* [6d265b](https://github.com/leanprover/lean4/commit/6d265b42b117eef78089f479790587a399da7690) fixes for `github.event.pull_request.merge_commit_sha` sometimes not being available.
+* [16cad2](https://github.com/leanprover/lean4/commit/16cad2b45c6a77efe4dce850dcdbaafaa7c91fc3) adds optimization for CI to not fetch complete history.
+* [#4544](https://github.com/leanprover/lean4/pull/4544) causes releases to be marked as prerelease on GitHub.
+* [#4446](https://github.com/leanprover/lean4/pull/4446) switches Lake to using `src/lake/lakefile.toml` to avoid needing to load a version of Lake to build Lake.
+* Nix
+  * [5eb5fa](https://github.com/leanprover/lean4/commit/5eb5fa49cf9862e99a5bccff8d4ca1a062f81900) fixes `update-stage0-commit` for Nix.
+  * [#4476](https://github.com/leanprover/lean4/pull/4476) adds gdb to Nix shell.
+  * [e665a0](https://github.com/leanprover/lean4/commit/e665a0d716dc42ba79b339b95e01eb99fe932cb3) fixes `update-stage0` for Nix.
+  * [4808eb](https://github.com/leanprover/lean4/commit/4808eb7c4bfb98f212b865f06a97d46c44978a61) fixes `cacheRoots` for Nix.
+  * [#3811](https://github.com/leanprover/lean4/pull/3811) adds platform-dependent flag to lib target.
+  * [#4587](https://github.com/leanprover/lean4/pull/4587) adds linking of `-lStd` back into nix build flags on darwin.
+
+### Breaking changes
+
+* `Char.csize` is replaced by `Char.utf8Size` ([#4357](https://github.com/leanprover/lean4/pull/4357)).
+* Library lemmas now are in terms of `(· == a)` over `(a == ·)` ([#3056](https://github.com/leanprover/lean4/pull/3056)).
+* Now the normal forms for indexing into `List` and `Array` is `xs[n]` and `xs[n]?` rather than using functions like `List.get` ([#4400](https://github.com/leanprover/lean4/pull/4400)).
+* Sometimes terms created via a sequence of unifications will be more eta reduced than before and proofs will require adaptation ([#4387](https://github.com/leanprover/lean4/pull/4387)).
+* The `GetElem` class has been split into two; see the docstrings for `GetElem` and `GetElem?` for more information ([#4560](https://github.com/leanprover/lean4/pull/4560)).
+
 
 v4.9.0
----------- 
+----------
 
 ### Language features, tactics, and metaprograms
 
@@ -40,6 +323,8 @@ v4.9.0
   * [#4395](https://github.com/leanprover/lean4/pull/4395) adds conservative fix for whitespace handling to avoid incremental reuse leading to goals in front of the text cursor being shown.
   * [#4407](https://github.com/leanprover/lean4/pull/4407) fixes non-incremental commands in macros blocking further incremental reporting.
   * [#4436](https://github.com/leanprover/lean4/pull/4436) fixes incremental reporting when there are nested tactics in terms.
+  * [#4459](https://github.com/leanprover/lean4/pull/4459) adds incrementality support for `next` and `if` tactics.
+  * [#4554](https://github.com/leanprover/lean4/pull/4554) disables incrementality for tactics in terms in tactics.
 * **Functional induction**
   * [#4135](https://github.com/leanprover/lean4/pull/4135) ensures that the names used for functional induction are reserved.
   * [#4327](https://github.com/leanprover/lean4/pull/4327) adds support for structural recursion on reflexive types.
@@ -85,7 +370,7 @@ v4.9.0
     When `index := false`, only the head function is taken into account, like in Lean 3.
     This feature can help users diagnose tricky simp failures or issues in code from libraries
     developed using Lean 3 and then ported to Lean 4.
-    
+
     In the following example, it will report that `foo` is a problematic theorem.
     ```lean
     opaque f : Nat → Nat → Nat
@@ -105,7 +390,7 @@ v4.9.0
     opaque f : Nat → Nat → Nat
 
     @[simp] theorem foo : f x (no_index (x, y).2) = y := by sorry
-    
+
     example : f a b ≤ b := by
       simp -- `foo` is still applied with `index := true`
     ```
@@ -123,6 +408,8 @@ v4.9.0
   * [#4267](https://github.com/leanprover/lean4/pull/4267) cases signature elaboration errors to show even if there are parse errors in the body.
   * [#4368](https://github.com/leanprover/lean4/pull/4368) improves error messages when numeric literals fail to synthesize an `OfNat` instance,
     including special messages warning when the expected type of the numeral can be a proposition.
+  * [#4643](https://github.com/leanprover/lean4/pull/4643) fixes issue leading to nested error messages and info trees vanishing, where snapshot subtrees were not restored on reuse.
+  * [#4657](https://github.com/leanprover/lean4/pull/4657) calculates error suppression per snapshot, letting elaboration errors appear even when there are later parse errors ([RFC #3556](https://github.com/leanprover/lean4/issues/3556)).
 * **Metaprogramming**
   * [#4167](https://github.com/leanprover/lean4/pull/4167) adds `Lean.MVarId.revertAll` to revert all free variables.
   * [#4169](https://github.com/leanprover/lean4/pull/4169) adds `Lean.MVarId.ensureNoMVar` to ensure the goal's target contains no expression metavariables.
@@ -239,6 +526,8 @@ v4.9.0
   * [#4192](https://github.com/leanprover/lean4/pull/4192) fixes restoration of infotrees when auto-bound implicit feature is activated,
     fixing a pretty printing error in hovers and strengthening the unused variable linter.
   * [dfb496](https://github.com/leanprover/lean4/commit/dfb496a27123c3864571aec72f6278e2dad1cecf) fixes `declareBuiltin` to allow it to be called multiple times per declaration.
+  * [#4569](https://github.com/leanprover/lean4/pull/4569) fixes an issue introduced in a merge conflict, where the interrupt exception was swallowed by some `tryCatchRuntimeEx` uses.
+  * [b056a0](https://github.com/leanprover/lean4/commit/b056a0b395bb728512a3f3e83bf9a093059d4301) adapts kernel interruption to the new cancellation system.
   * Cleanup: [#4112](https://github.com/leanprover/lean4/pull/4112), [#4126](https://github.com/leanprover/lean4/pull/4126), [#4091](https://github.com/leanprover/lean4/pull/4091), [#4139](https://github.com/leanprover/lean4/pull/4139), [#4153](https://github.com/leanprover/lean4/pull/4153).
   * Tests: [030406](https://github.com/leanprover/lean4/commit/03040618b8f9b35b7b757858483e57340900cdc4), [#4133](https://github.com/leanprover/lean4/pull/4133).
 
@@ -249,6 +538,7 @@ v4.9.0
 * [#3915](https://github.com/leanprover/lean4/pull/3915) documents the runtime memory layout for inductive types.
 
 ### Lake
+* [#4518](https://github.com/leanprover/lean4/pull/4518) makes trace reading more robust. Lake now rebuilds if trace files are invalid or unreadable and is backwards compatible with previous pure numeric traces.
 * [#4057](https://github.com/leanprover/lean4/pull/4057) adds support for docstrings on `require` commands.
 * [#4088](https://github.com/leanprover/lean4/pull/4088) improves hovers for `family_def` and `library_data` commands.
 * [#4147](https://github.com/leanprover/lean4/pull/4147) adds default `README.md` to package templates
@@ -298,12 +588,14 @@ v4.9.0
 * [#4333](https://github.com/leanprover/lean4/pull/4333) adjusts workflow to update Batteries in manifest when creating `lean-pr-testing-NNNN` Mathlib branches.
 * [#4355](https://github.com/leanprover/lean4/pull/4355) simplifies `lean4checker` step of release checklist.
 * [#4361](https://github.com/leanprover/lean4/pull/4361) adds installing elan to `pr-release` CI step.
+* [#4628](https://github.com/leanprover/lean4/pull/4628) fixes the Windows build, which was missing an exported symbol.
 
 ### Breaking changes
 While most changes could be considered to be a breaking change, this section makes special note of API changes.
 
 * `Nat.zero_or` and `Nat.or_zero` have been swapped ([#4094](https://github.com/leanprover/lean4/pull/4094)).
 * `IsLawfulSingleton` is now `LawfulSingleton` ([#4350](https://github.com/leanprover/lean4/pull/4350)).
+* The `BitVec` literal notation is now `<num>#<term>` rather than `<term>#<term>`, and it is global rather than scoped. Use `BitVec.ofNat w x` rather than `x#w` when `x` is a not a numeric literal ([0d3051](https://github.com/leanprover/lean4/commit/0d30517dca094a07bcb462252f718e713b93ffba)).
 * `BitVec.rotateLeft` and `BitVec.rotateRight` now take the shift modulo the bitwidth ([#4229](https://github.com/leanprover/lean4/pull/4229)).
 * These are no longer simp lemmas:
   `List.length_pos` ([#4172](https://github.com/leanprover/lean4/pull/4172)),

doc/dev/debugging.md

@@ -5,7 +5,7 @@ Some notes on how to debug Lean, which may also be applicable to debugging Lean
 
 ## Tracing
 
-In `CoreM` and derived monads, we use `trace![traceCls] "msg with {interpolations}"` to fill the structured trace viewable with `set_option trace.traceCls true`.
+In `CoreM` and derived monads, we use `trace[traceCls] "msg with {interpolations}"` to fill the structured trace viewable with `set_option trace.traceCls true`.
 New trace classes have to be registered using `registerTraceClass` first.
 
 Notable trace classes:
@@ -22,7 +22,9 @@ Notable trace classes:
 
 In pure contexts or when execution is aborted before the messages are finally printed, one can instead use the term `dbg_trace "msg with {interpolations}"; val` (`;` can also be replaced by a newline), which will print the message to stderr before evaluating `val`. `dbgTraceVal val` can be used as a shorthand for `dbg_trace "{val}"; val`.
 Note that if the return value is not actually used, the trace code is silently dropped as well.
-In the language server, stderr output is buffered and shown as messages after a command has been elaborated, unless the option `server.stderrAsMessages` is deactivated.
+
+By default, such stderr output is buffered and shown as messages after a command has been elaborated, which is necessary to ensure deterministic ordering of messages under parallelism.
+If Lean aborts the process before it can finish the command or takes too long to do that, using `-DstderrAsMessages=false` avoids this buffering and shows `dbg_trace` output (but not `trace`s or other diagnostics) immediately.
 
 ## Debuggers
 

doc/dev/release_checklist.md

@@ -5,8 +5,11 @@ 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 (1) someone has written the release notes and (2) someone has written the first draft of the release blog post.
-  If there is any material in `./releases_drafts/`, then the release notes are not done. (See the section "Writing the release notes".)
+- One week before the planned release, ensure that
+  (1) someone has written the release notes and
+  (2) someone has written the first draft of the release blog post.
+  If there is any material in `./releases_drafts/` on the `releases/v4.6.0` branch, then the release notes are not done.
+  (See the section "Writing the release notes".)
 - `git checkout releases/v4.6.0`
   (This branch should already exist, from the release candidates.)
 - `git pull`
@@ -144,33 +147,31 @@ We'll use `v4.7.0-rc1` as the intended release version in this example.
   - 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.
 - (GitHub release notes) 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".
-  - If release notes have been written already, copy the section of `RELEASES.md` for this version into the Github release notes
-    and use the title "Changes since v4.6.0 (from RELEASES.md)".
-  - Otherwise, in the "previous tag" dropdown, select `v4.6.0`, and click "Generate release notes".
+  - Verify that the release is marked as a prerelease (this should have been done automatically by the CI release job).
+  - 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.
+  - This assumes that for each repository either:
+    * There is already a *reviewed* branch `bump/v4.7.0` containing the required adaptations.
+      The preparation of this branch is beyond the scope of this document.
+    * The repository does not need any changes to move to the new version.
   - 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.
+    - If the repository does not need any changes (i.e. `bump/v4.7.0` does not exist) then create
+      a new PR updating `lean-toolchain` to `leanprover/lean4:v4.7.0-rc1` and running `lake update`.
+    - Otherwise:
+      - 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 the 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!
@@ -187,9 +188,11 @@ We'll use `v4.7.0-rc1` as the intended release version in this example.
   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)`
+  - Replaces the "release notes will be copied" text in the `v4.6.0` section of `RELEASES.md` with the
+    finalized release notes from the `releases/v4.6.0` branch.
   - Replaces the "development in progress" in the `v4.7.0` section of `RELEASES.md` with
     ```
-    Release candidate, release notes will be copied from `branch releases/v4.7.0` once completed.
+    Release candidate, release notes will be copied from the branch `releases/v4.7.0` once completed.
     ```
     and inserts the following section before that section:
     ```
@@ -198,6 +201,8 @@ We'll use `v4.7.0-rc1` as the intended release version in this example.
     Development in progress.
     ```
   - Removes all the entries from the `./releases_drafts/` folder.
+  - Titled "chore: begin development cycle for v4.8.0"
+
 
 ## Time estimates:
 Slightly longer than the corresponding steps for a stable release.
@@ -222,12 +227,15 @@ Please read https://leanprover-community.github.io/contribute/tags_and_branches.
   * 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:
+* Once `nightly-testing` is working on a given nightly, say `nightly-2024-02-15`, we will create a PR to `bump/v4.7.0`.
+* For Mathlib, there is a script in `scripts/create-adaptation-pr.sh` that automates this process.
+* For Batteries and Aesop it is currently manual.
+* For all of these repositories, the process is the same:
   * 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`.
+  * In that branch, `git merge 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`.
+  * 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!
@@ -239,7 +247,7 @@ The exact steps are a work in progress.
 Here is the general idea:
 
 * The work is done right on the `releases/v4.6.0` branch sometime after it is created but before the stable release is made.
-  The release notes for `v4.6.0` will be copied to `master`.
+  The release notes for `v4.6.0` will later be copied to `master` when we begin a new development cycle.
 * There can be material for release notes entries in commit messages.
 * There can also be pre-written entries in `./releases_drafts`, which should be all incorporated in the release notes and then deleted from the branch.
   See `./releases_drafts/README.md` for more information.

doc/examples/interp.lean

@@ -149,4 +149,4 @@ def fact : Expr ctx (Ty.fn Ty.int Ty.int) :=
            (op (·*·) (delay fun _ => app fact (op (·-·) (var stop) (val 1))) (var stop)))
   decreasing_by sorry
 
-#eval fact.interp Env.nil 10
+#eval! fact.interp Env.nil 10

doc/flake.lock

@@ -18,12 +18,15 @@
       }
     },
     "flake-utils": {
+      "inputs": {
+        "systems": "systems"
+      },
       "locked": {
-        "lastModified": 1656928814,
-        "narHash": "sha256-RIFfgBuKz6Hp89yRr7+NR5tzIAbn52h8vT6vXkYjZoM=",
+        "lastModified": 1710146030,
+        "narHash": "sha256-SZ5L6eA7HJ/nmkzGG7/ISclqe6oZdOZTNoesiInkXPQ=",
         "owner": "numtide",
         "repo": "flake-utils",
-        "rev": "7e2a3b3dfd9af950a856d66b0a7d01e3c18aa249",
+        "rev": "b1d9ab70662946ef0850d488da1c9019f3a9752a",
         "type": "github"
       },
       "original": {
@@ -35,13 +38,12 @@
     "lean": {
       "inputs": {
         "flake-utils": "flake-utils",
-        "lean4-mode": "lean4-mode",
-        "nix": "nix",
-        "nixpkgs": "nixpkgs_2"
+        "nixpkgs": "nixpkgs",
+        "nixpkgs-old": "nixpkgs-old"
       },
       "locked": {
         "lastModified": 0,
-        "narHash": "sha256-YnYbmG0oou1Q/GE4JbMNb8/yqUVXBPIvcdQQJHBqtPk=",
+        "narHash": "sha256-saRAtQ6VautVXKDw1XH35qwP0KEBKTKZbg/TRa4N9Vw=",
         "path": "../.",
         "type": "path"
       },
@@ -50,22 +52,6 @@
         "type": "path"
       }
     },
-    "lean4-mode": {
-      "flake": false,
-      "locked": {
-        "lastModified": 1659020985,
-        "narHash": "sha256-+dRaXB7uvN/weSZiKcfSKWhcdJVNg9Vg8k0pJkDNjpc=",
-        "owner": "leanprover",
-        "repo": "lean4-mode",
-        "rev": "37d5c99b7b29c80ab78321edd6773200deb0bca6",
-        "type": "github"
-      },
-      "original": {
-        "owner": "leanprover",
-        "repo": "lean4-mode",
-        "type": "github"
-      }
-    },
     "leanInk": {
       "flake": false,
       "locked": {
@@ -83,22 +69,6 @@
         "type": "github"
       }
     },
-    "lowdown-src": {
-      "flake": false,
-      "locked": {
-        "lastModified": 1633514407,
-        "narHash": "sha256-Dw32tiMjdK9t3ETl5fzGrutQTzh2rufgZV4A/BbxuD4=",
-        "owner": "kristapsdz",
-        "repo": "lowdown",
-        "rev": "d2c2b44ff6c27b936ec27358a2653caaef8f73b8",
-        "type": "github"
-      },
-      "original": {
-        "owner": "kristapsdz",
-        "repo": "lowdown",
-        "type": "github"
-      }
-    },
     "mdBook": {
       "flake": false,
       "locked": {
@@ -115,65 +85,13 @@
         "type": "github"
       }
     },
-    "nix": {
-      "inputs": {
-        "lowdown-src": "lowdown-src",
-        "nixpkgs": "nixpkgs",
-        "nixpkgs-regression": "nixpkgs-regression"
-      },
-      "locked": {
-        "lastModified": 1657097207,
-        "narHash": "sha256-SmeGmjWM3fEed3kQjqIAO8VpGmkC2sL1aPE7kKpK650=",
-        "owner": "NixOS",
-        "repo": "nix",
-        "rev": "f6316b49a0c37172bca87ede6ea8144d7d89832f",
-        "type": "github"
-      },
-      "original": {
-        "owner": "NixOS",
-        "repo": "nix",
-        "type": "github"
-      }
-    },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1653988320,
-        "narHash": "sha256-ZaqFFsSDipZ6KVqriwM34T739+KLYJvNmCWzErjAg7c=",
+        "lastModified": 1710889954,
+        "narHash": "sha256-Pr6F5Pmd7JnNEMHHmspZ0qVqIBVxyZ13ik1pJtm2QXk=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "2fa57ed190fd6c7c746319444f34b5917666e5c1",
-        "type": "github"
-      },
-      "original": {
-        "owner": "NixOS",
-        "ref": "nixos-22.05-small",
-        "repo": "nixpkgs",
-        "type": "github"
-      }
-    },
-    "nixpkgs-regression": {
-      "locked": {
-        "lastModified": 1643052045,
-        "narHash": "sha256-uGJ0VXIhWKGXxkeNnq4TvV3CIOkUJ3PAoLZ3HMzNVMw=",
-        "owner": "NixOS",
-        "repo": "nixpkgs",
-        "rev": "215d4d0fd80ca5163643b03a33fde804a29cc1e2",
-        "type": "github"
-      },
-      "original": {
-        "owner": "NixOS",
-        "repo": "nixpkgs",
-        "rev": "215d4d0fd80ca5163643b03a33fde804a29cc1e2",
-        "type": "github"
-      }
-    },
-    "nixpkgs_2": {
-      "locked": {
-        "lastModified": 1657208011,
-        "narHash": "sha256-BlIFwopAykvdy1DYayEkj6ZZdkn+cVgPNX98QVLc0jM=",
-        "owner": "NixOS",
-        "repo": "nixpkgs",
-        "rev": "2770cc0b1e8faa0e20eb2c6aea64c256a706d4f2",
+        "rev": "7872526e9c5332274ea5932a0c3270d6e4724f3b",
         "type": "github"
       },
       "original": {
@@ -183,6 +101,23 @@
         "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"
+      }
+    },
     "root": {
       "inputs": {
         "alectryon": "alectryon",
@@ -194,6 +129,21 @@
         "leanInk": "leanInk",
         "mdBook": "mdBook"
       }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
     }
   },
   "root": "root",

doc/flake.nix

@@ -17,7 +17,7 @@
   };
 
   outputs = inputs@{ self, ... }: inputs.flake-utils.lib.eachDefaultSystem (system:
-    with inputs.lean.packages.${system}; with nixpkgs;
+    with inputs.lean.packages.${system}.deprecated; with nixpkgs;
     let
       doc-src = lib.sourceByRegex ../. ["doc.*" "tests(/lean(/beginEndAsMacro.lean)?)?"];
     in {
@@ -44,21 +44,6 @@
           mdbook build -d $out
         '';
       };
-      # We use a separate derivation instead of `checkPhase` so we can push it but not `doc` to the binary cache
-      test = stdenv.mkDerivation {
-        name ="lean-doc-test";
-        src = doc-src;
-        buildInputs = [ lean-mdbook stage1.Lean.lean-package strace ];
-        patchPhase = ''
-          cd doc
-          patchShebangs test
-        '';
-        buildPhase = ''
-          mdbook test
-          touch $out
-        '';
-        dontInstall = true;
-      };
       leanInk = (buildLeanPackage {
         name = "Main";
         src = inputs.leanInk;

doc/int.md

@@ -13,7 +13,7 @@ Recall that nonnegative numerals are considered to be a `Nat` if there are no ty
 
 The operator `/` for `Int` implements integer division.
 ```lean
-#eval -10 / 4 -- -2
+#eval -10 / 4 -- -3
 ```
 
 Similar to `Nat`, the internal representation of `Int` is optimized. Small integers are

doc/make/index.md

@@ -8,6 +8,7 @@ Requirements
 - C++14 compatible compiler
 - [CMake](http://www.cmake.org)
 - [GMP (GNU multiprecision library)](http://gmplib.org/)
+- [LibUV](https://libuv.org/)
 
 Platform-Specific Setup
 -----------------------
@@ -27,9 +28,9 @@ Setting up a basic parallelized release build:
 git clone https://github.com/leanprover/lean4
 cd lean4
 cmake --preset release
-make -C build/release -j$(nproc)  # see below for macOS
+make -C build/release -j$(nproc || sysctl -n hw.logicalcpu)
 ```
-You can replace `$(nproc)`, which is not available on macOS and some alternative shells, with the desired parallelism amount.
+You can replace `$(nproc || sysctl -n hw.logicalcpu)` with the desired parallelism amount.
 
 The above commands will compile the Lean library and binaries into the
 `stage1` subfolder; see below for details.

doc/make/msys2.md

@@ -25,7 +25,7 @@ MSYS2 has a package management system, [pacman][pacman], which is used in Arch L
 Here are the commands to install all dependencies needed to compile Lean on your machine.
 
 ```bash
-pacman -S make python mingw-w64-x86_64-cmake mingw-w64-x86_64-clang mingw-w64-x86_64-ccache git unzip diffutils binutils
+pacman -S make python mingw-w64-x86_64-cmake mingw-w64-x86_64-clang mingw-w64-x86_64-ccache mingw-w64-x86_64-libuv mingw-w64-x86_64-gmp git unzip diffutils binutils
 ```
 
 You should now be able to run these commands:
@@ -64,6 +64,7 @@ they are installed in your MSYS setup:
 - libgcc_s_seh-1.dll
 - libstdc++-6.dll
 - libgmp-10.dll
+- libuv-1.dll
 - libwinpthread-1.dll
 
 The following linux command will do that:

doc/make/osx-10.9.md

@@ -32,15 +32,16 @@ following to use `g++`.
 cmake -DCMAKE_CXX_COMPILER=g++ ...
 ```
 
-## Required Packages: CMake, GMP
+## Required Packages: CMake, GMP, libuv
 
 ```bash
 brew install cmake
 brew install gmp
+brew install libuv
 ```
 
 ## Recommended Packages: CCache
 
 ```bash
 brew install ccache
-```
+```

doc/make/ubuntu.md

@@ -8,5 +8,5 @@ follow the [generic build instructions](index.md).
 ## Basic packages
 
 ```bash
-sudo apt-get install git libgmp-dev cmake ccache clang
+sudo apt-get install git libgmp-dev libuv1-dev cmake ccache clang
 ```

doc/quickstart.md

@@ -7,12 +7,17 @@ See [Setup](./setup.md) for supported platforms and other ways to set up Lean 4.
 
 1. Launch VS Code and install the `lean4` extension by clicking on the "Extensions" sidebar entry and searching for "lean4".
 
-    ![installing the vscode-lean4 extension](images/code-ext.png)
+   ![installing the vscode-lean4 extension](images/code-ext.png)
 
-1. Open the Lean 4 setup guide by creating a new text file using "File > New Text File" (`Ctrl+N`), clicking on the ∀-symbol in the top right and selecting "Documentation… > Setup: Show Setup Guide".
+1. Open the Lean 4 setup guide by creating a new text file using "File > New Text File" (`Ctrl+N` / `Cmd+N`), clicking on the ∀-symbol in the top right and selecting "Documentation… > Docs: Show Setup Guide".
 
-    ![show setup guide](images/show-setup-guide.png)
+   ![show setup guide](images/show-setup-guide.png)
 
-1. Follow the Lean 4 setup guide. It will walk you through learning resources for Lean 4, teach you how to set up Lean's dependencies on your platform, install Lean 4 for you at the click of a button and help you set up your first project.
+1. Follow the Lean 4 setup guide. It will:
 
-    ![setup guide](images/setup_guide.png)
+   - walk you through learning resources for Lean,
+   - teach you how to set up Lean's dependencies on your platform,
+   - install Lean 4 for you at the click of a button,
+   - help you set up your first project.
+
+   ![setup guide](images/setup_guide.png)

flake.lock

@@ -1,21 +1,5 @@
 {
   "nodes": {
-    "flake-compat": {
-      "flake": false,
-      "locked": {
-        "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"
@@ -34,71 +18,18 @@
         "type": "github"
       }
     },
-    "lean4-mode": {
-      "flake": false,
-      "locked": {
-        "lastModified": 1709737301,
-        "narHash": "sha256-uT9JN2kLNKJK9c/S/WxLjiHmwijq49EgLb+gJUSDpz0=",
-        "owner": "leanprover",
-        "repo": "lean4-mode",
-        "rev": "f1f24c15134dee3754b82c9d9924866fe6bc6b9f",
-        "type": "github"
-      },
-      "original": {
-        "owner": "leanprover",
-        "repo": "lean4-mode",
-        "type": "github"
-      }
-    },
-    "libgit2": {
-      "flake": false,
-      "locked": {
-        "lastModified": 1697646580,
-        "narHash": "sha256-oX4Z3S9WtJlwvj0uH9HlYcWv+x1hqp8mhXl7HsLu2f0=",
-        "owner": "libgit2",
-        "repo": "libgit2",
-        "rev": "45fd9ed7ae1a9b74b957ef4f337bc3c8b3df01b5",
-        "type": "github"
-      },
-      "original": {
-        "owner": "libgit2",
-        "repo": "libgit2",
-        "type": "github"
-      }
-    },
-    "nix": {
-      "inputs": {
-        "flake-compat": "flake-compat",
-        "libgit2": "libgit2",
-        "nixpkgs": "nixpkgs",
-        "nixpkgs-regression": "nixpkgs-regression"
-      },
-      "locked": {
-        "lastModified": 1711102798,
-        "narHash": "sha256-CXOIJr8byjolqG7eqCLa+Wfi7rah62VmLoqSXENaZnw=",
-        "owner": "NixOS",
-        "repo": "nix",
-        "rev": "a22328066416650471c3545b0b138669ea212ab4",
-        "type": "github"
-      },
-      "original": {
-        "owner": "NixOS",
-        "repo": "nix",
-        "type": "github"
-      }
-    },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1709083642,
-        "narHash": "sha256-7kkJQd4rZ+vFrzWu8sTRtta5D1kBG0LSRYAfhtmMlSo=",
+        "lastModified": 1710889954,
+        "narHash": "sha256-Pr6F5Pmd7JnNEMHHmspZ0qVqIBVxyZ13ik1pJtm2QXk=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "b550fe4b4776908ac2a861124307045f8e717c8e",
+        "rev": "7872526e9c5332274ea5932a0c3270d6e4724f3b",
         "type": "github"
       },
       "original": {
         "owner": "NixOS",
-        "ref": "release-23.11",
+        "ref": "nixpkgs-unstable",
         "repo": "nixpkgs",
         "type": "github"
       }
@@ -120,44 +51,10 @@
         "type": "github"
       }
     },
-    "nixpkgs-regression": {
-      "locked": {
-        "lastModified": 1643052045,
-        "narHash": "sha256-uGJ0VXIhWKGXxkeNnq4TvV3CIOkUJ3PAoLZ3HMzNVMw=",
-        "owner": "NixOS",
-        "repo": "nixpkgs",
-        "rev": "215d4d0fd80ca5163643b03a33fde804a29cc1e2",
-        "type": "github"
-      },
-      "original": {
-        "owner": "NixOS",
-        "repo": "nixpkgs",
-        "rev": "215d4d0fd80ca5163643b03a33fde804a29cc1e2",
-        "type": "github"
-      }
-    },
-    "nixpkgs_2": {
-      "locked": {
-        "lastModified": 1710889954,
-        "narHash": "sha256-Pr6F5Pmd7JnNEMHHmspZ0qVqIBVxyZ13ik1pJtm2QXk=",
-        "owner": "NixOS",
-        "repo": "nixpkgs",
-        "rev": "7872526e9c5332274ea5932a0c3270d6e4724f3b",
-        "type": "github"
-      },
-      "original": {
-        "owner": "NixOS",
-        "ref": "nixpkgs-unstable",
-        "repo": "nixpkgs",
-        "type": "github"
-      }
-    },
     "root": {
       "inputs": {
         "flake-utils": "flake-utils",
-        "lean4-mode": "lean4-mode",
-        "nix": "nix",
-        "nixpkgs": "nixpkgs_2",
+        "nixpkgs": "nixpkgs",
         "nixpkgs-old": "nixpkgs-old"
       }
     },

flake.nix

@@ -1,44 +1,27 @@
 {
-  description = "Lean interactive theorem prover";
+  description = "Lean development flake. Not intended for end users.";
 
   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 = {
-    url = "github:leanprover/lean4-mode";
-    flake = false;
-  };
-  # used *only* by `stage0-from-input` below
-  #inputs.lean-stage0 = {
-  #  url = github:leanprover/lean4;
-  #  inputs.nixpkgs.follows = "nixpkgs";
-  #  inputs.flake-utils.follows = "flake-utils";
-  #  inputs.nix.follows = "nix";
-  #  inputs.lean4-mode.follows = "lean4-mode";
-  #};
 
-  outputs = { self, nixpkgs, nixpkgs-old, flake-utils, nix, lean4-mode, ... }@inputs: flake-utils.lib.eachDefaultSystem (system:
+  outputs = { self, nixpkgs, nixpkgs-old, flake-utils, ... }@inputs: flake-utils.lib.eachDefaultSystem (system:
     let
-      pkgs = import nixpkgs {
-        inherit system;
-        # for `vscode-with-extensions`
-        config.allowUnfree = true;
-      };
+      pkgs = import nixpkgs { inherit system; };
       # 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; };
+      lean-packages = pkgs.callPackage (./nix/packages.nix) { src = ./.; };
 
       devShellWithDist = pkgsDist: pkgs.mkShell.override {
           stdenv = pkgs.overrideCC pkgs.stdenv lean-packages.llvmPackages.clang;
         } ({
           buildInputs = with pkgs; [
-            cmake gmp ccache
+            cmake gmp libuv ccache
             lean-packages.llvmPackages.llvm  # llvm-symbolizer for asan/lsan
             gdb
             # TODO: only add when proven to not affect the flakification
@@ -51,6 +34,7 @@
           CTEST_OUTPUT_ON_FAILURE = 1;
         } // pkgs.lib.optionalAttrs pkgs.stdenv.isLinux {
           GMP = pkgsDist.gmp.override { withStatic = true; };
+          LIBUV = pkgsDist.libuv.overrideAttrs (attrs: { configureFlags = ["--enable-static"]; });
           GLIBC = pkgsDist.glibc;
           GLIBC_DEV = pkgsDist.glibc.dev;
           GCC_LIB = pkgsDist.gcc.cc.lib;
@@ -58,41 +42,15 @@
           GDB = pkgsDist.gdb;
         });
     in {
-      packages = lean-packages // rec {
-        debug = lean-packages.override { debug = true; };
-        stage0debug = lean-packages.override { stage0debug = true; };
-        asan = lean-packages.override { extraCMakeFlags = [ "-DLEAN_EXTRA_CXX_FLAGS=-fsanitize=address" "-DLEANC_EXTRA_FLAGS=-fsanitize=address" "-DSMALL_ALLOCATOR=OFF" "-DSYMBOLIC=OFF" ]; };
-        asandebug = asan.override { debug = true; };
-        tsan = lean-packages.override {
-          extraCMakeFlags = [ "-DLEAN_EXTRA_CXX_FLAGS=-fsanitize=thread" "-DLEANC_EXTRA_FLAGS=-fsanitize=thread" "-DCOMPRESSED_OBJECT_HEADER=OFF" ];
-          stage0 = (lean-packages.override {
-            # Compressed headers currently trigger data race reports in tsan.
-            # Turn them off for stage 0 as well so stage 1 can read its own stdlib.
-            extraCMakeFlags = [ "-DCOMPRESSED_OBJECT_HEADER=OFF" ];
-          }).stage1;
-        };
-        tsandebug = tsan.override { debug = true; };
-        stage0-from-input = lean-packages.override {
-          stage0 = pkgs.writeShellScriptBin "lean" ''
-            exec ${inputs.lean-stage0.packages.${system}.lean}/bin/lean -Dinterpreter.prefer_native=false "$@"
-          '';
-        };
-        inherit self;
+      packages = {
+        # to be removed when Nix CI is not needed anymore
+        inherit (lean-packages) cacheRoots test update-stage0-commit ciShell;
+        deprecated = lean-packages;
       };
-      defaultPackage = lean-packages.lean-all;
 
       # 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 {
-      templates.pkg = {
-        path = ./nix/templates/pkg;
-        description = "A custom Lean package";
-      };
-
-      defaultTemplate = templates.pkg;
-    };
+    });
 }

nix/bootstrap.nix

@@ -1,13 +1,13 @@
 { src, debug ? false, stage0debug ? false, extraCMakeFlags ? [],
-  stdenv, lib, cmake, gmp, git, gnumake, bash, buildLeanPackage, writeShellScriptBin, runCommand, symlinkJoin, lndir, perl, gnused, darwin, llvmPackages, linkFarmFromDrvs,
+  stdenv, lib, cmake, gmp, libuv, git, gnumake, bash, buildLeanPackage, writeShellScriptBin, runCommand, symlinkJoin, lndir, perl, gnused, darwin, llvmPackages, linkFarmFromDrvs,
   ... } @ args:
 with builtins;
-rec {
+lib.warn "The Nix-based build is deprecated" rec {
   inherit stdenv;
   sourceByRegex = p: rs: lib.sourceByRegex p (map (r: "(/src/)?${r}") rs);
   buildCMake = args: stdenv.mkDerivation ({
     nativeBuildInputs = [ cmake ];
-    buildInputs = [ gmp llvmPackages.llvm ];
+    buildInputs = [ gmp libuv llvmPackages.llvm ];
     # https://github.com/NixOS/nixpkgs/issues/60919
     hardeningDisable = [ "all" ];
     dontStrip = (args.debug or debug);
@@ -26,11 +26,7 @@ rec {
   lean-bin-tools-unwrapped = buildCMake {
     name = "lean-bin-tools";
     outputs = [ "out" "leanc_src" ];
-    realSrc = sourceByRegex (src + "/src") [ "CMakeLists\.txt" "cmake.*" "bin.*" "include.*" ".*\.in" "Leanc\.lean" ];
-    preConfigure = ''
-      touch empty.cpp
-      sed -i 's/add_subdirectory.*//;s/set(LEAN_OBJS.*/set(LEAN_OBJS empty.cpp)/' CMakeLists.txt
-    '';
+    realSrc = sourceByRegex (src + "/src") [ "CMakeLists\.txt" "[a-z].*" ".*\.in" "Leanc\.lean" ];
     dontBuild = true;
     installPhase = ''
       mkdir $out $leanc_src
@@ -45,11 +41,10 @@ rec {
   leancpp = buildCMake {
     name = "leancpp";
     src = src + "/src";
-    buildFlags = [ "leancpp" "leanrt" "leanrt_initial-exec" "shell" ];
+    buildFlags = [ "leancpp" "leanrt" "leanrt_initial-exec" "leanshell" "leanmain" ];
     installPhase = ''
       mkdir -p $out
       mv lib/ $out/
-      mv shell/CMakeFiles/shell.dir/lean.cpp.o $out/lib
       mv runtime/libleanrt_initial-exec.a $out/lib
     '';
   };
@@ -122,12 +117,15 @@ rec {
         touch empty.c
         ${stdenv.cc}/bin/cc -shared -o $out/$libName empty.c
       '';
+      leanshared_1 = runCommand "leanshared_1" { buildInputs = [ stdenv.cc ]; libName = "leanshared_1${stdenv.hostPlatform.extensions.sharedLibrary}"; } ''
+        mkdir $out
+        touch empty.c
+        ${stdenv.cc}/bin/cc -shared -o $out/$libName empty.c
+      '';
       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,${Std.staticLib}/libStd.a -Wl,-force_load,${Lean.staticLib}/libLean.a -Wl,-force_load,${leancpp}/lib/lean/libleancpp.a ${leancpp}/lib/libleanrt_initial-exec.a -lc++"
-            else "-Wl,--whole-archive -lInit -lStd -lLean -lleancpp ${leancpp}/lib/libleanrt_initial-exec.a -Wl,--no-whole-archive -lstdc++"} \
+          -Wl,--whole-archive ${leancpp}/lib/temp/libleanshell.a -lInit -lStd -lLean -lleancpp ${leancpp}/lib/libleanrt_initial-exec.a -Wl,--no-whole-archive -lstdc++ \
           -lm ${stdlibLinkFlags} \
           $(${llvmPackages.libllvm.dev}/bin/llvm-config --ldflags --libs) \
           -o $out/$libName
@@ -135,18 +133,18 @@ rec {
       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 ${stdlibLinkFlags} -L${libInit_shared} -L${leanshared} "$@"
+        LEAN_CC=${stdenv.cc}/bin/cc ${Leanc.executable}/bin/leanc -I${lean-bin-tools-unwrapped}/include ${stdlibLinkFlags} -L${libInit_shared} -L${leanshared_1} -L${leanshared} "$@"
       '';
       lean = runCommand "lean" { buildInputs = lib.optional stdenv.isDarwin darwin.cctools; } ''
         mkdir -p $out/bin
-        ${leanc}/bin/leanc ${leancpp}/lib/lean.cpp.o ${libInit_shared}/* ${leanshared}/* -o $out/bin/lean
+        ${leanc}/bin/leanc ${leancpp}/lib/temp/libleanmain.a ${libInit_shared}/* ${leanshared_1}/* ${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)} ${libInit_shared}/* ${leanshared}/* $out/lib/lean/
+          ln -sf ${leancpp}/lib/lean/* ${lib.concatMapStringsSep " " (l: "${l.modRoot}/* ${l.staticLib}/*") (lib.reverseList stdlib)} ${libInit_shared}/* ${leanshared_1}/* ${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 $out/bin
           # NOTE: `lndir` will not override existing `bin/leanc`
@@ -160,7 +158,7 @@ rec {
       test = buildCMake {
         name = "lean-test-${desc}";
         realSrc = lib.sourceByRegex src [ "src.*" "tests.*" ];
-        buildInputs = [ gmp perl git ];
+        buildInputs = [ gmp libuv perl git ];
         preConfigure = ''
           cd src
         '';
@@ -171,7 +169,7 @@ rec {
           ln -sf ${lean-all}/* .
         '';
         buildPhase = ''
-          ctest --output-junit test-results.xml --output-on-failure -E 'leancomptest_(doc_example|foreign)' -j$NIX_BUILD_CORES
+          ctest --output-junit test-results.xml --output-on-failure -E 'leancomptest_(doc_example|foreign)|leanlaketest_reverse-ffi' -j$NIX_BUILD_CORES
         '';
         installPhase = ''
           mkdir $out

nix/buildLeanPackage.nix

@@ -1,5 +1,5 @@
 { lean, lean-leanDeps ? lean, lean-final ? lean, leanc,
-  stdenv, lib, coreutils, gnused, writeShellScriptBin, bash, lean-emacs, lean-vscode, nix, substituteAll, symlinkJoin, linkFarmFromDrvs,
+  stdenv, lib, coreutils, gnused, writeShellScriptBin, bash, substituteAll, symlinkJoin, linkFarmFromDrvs,
   runCommand, darwin, mkShell, ... }:
 let lean-final' = lean-final; in
 lib.makeOverridable (
@@ -197,19 +197,6 @@ with builtins; let
              then map (m: m.module) header.imports
              else abort "errors while parsing imports of ${mod}:\n${lib.concatStringsSep "\n" header.errors}";
     in mkMod mod (map (dep: if modDepsMap ? ${dep} then modCandidates.${dep} else externalModMap.${dep}) deps)) modDepsMap;
-  makeEmacsWrapper = name: emacs: lean: writeShellScriptBin name ''
-    ${emacs} --eval "(progn (setq lean4-rootdir \"${lean}\"))" "$@"
-  '';
-  makeVSCodeWrapper = name: lean: writeShellScriptBin name ''
-    PATH=${lean}/bin:$PATH ${lean-vscode}/bin/code "$@"
-  '';
-  printPaths = deps: writeShellScriptBin "print-paths" ''
-    echo '${toJSON {
-      oleanPath = [(depRoot "print-paths" deps)];
-      srcPath = ["."] ++ map (dep: dep.src) allExternalDeps;
-      loadDynlibPaths = map pathOfSharedLib (loadDynlibsOfDeps deps);
-    }}'
-  '';
   expandGlob = g:
     if typeOf g == "string" then [g]
     else if g.glob == "one" then [g.mod]
@@ -257,48 +244,4 @@ in rec {
         -o $out/bin/${executableName} \
         ${lib.concatStringsSep " " allLinkFlags}
     '') {};
-
-  lean-package = writeShellScriptBin "lean" ''
-    LEAN_PATH=${modRoot}:$LEAN_PATH LEAN_SRC_PATH=$LEAN_SRC_PATH:${src} exec ${lean-final}/bin/lean "$@"
-  '';
-  emacs-package = makeEmacsWrapper "emacs-package" lean-package;
-  vscode-package = makeVSCodeWrapper "vscode-package" lean-package;
-
-  link-ilean = writeShellScriptBin "link-ilean" ''
-    dest=''${1:-.}
-    mkdir -p $dest/build/lib
-    ln -sf ${iTree}/* $dest/build/lib
-  '';
-
-  makePrintPathsFor = deps: mods: printPaths deps // mapAttrs (_: mod: makePrintPathsFor (deps ++ [mod]) mods) mods;
-  print-paths = makePrintPathsFor [] (mods' // externalModMap);
-  # `lean` wrapper that dynamically runs Nix for the actual `lean` executable so the same editor can be
-  # used for multiple projects/after upgrading the `lean` input/for editing both stage 1 and the tests
-  lean-bin-dev = substituteAll {
-    name = "lean";
-    dir = "bin";
-    src = ./lean-dev.in;
-    isExecutable = true;
-    srcRoot = fullSrc;  # use root flake.nix in case of Lean repo
-    inherit bash nix srcTarget srcArgs;
-  };
-  lake-dev = substituteAll {
-    name = "lake";
-    dir = "bin";
-    src = ./lake-dev.in;
-    isExecutable = true;
-    srcRoot = fullSrc;  # use root flake.nix in case of Lean repo
-    inherit bash nix srcTarget srcArgs;
-  };
-  lean-dev = symlinkJoin { name = "lean-dev"; paths = [ lean-bin-dev lake-dev ]; };
-  emacs-dev = makeEmacsWrapper "emacs-dev" "${lean-emacs}/bin/emacs" lean-dev;
-  emacs-path-dev = makeEmacsWrapper "emacs-path-dev" "emacs" lean-dev;
-  vscode-dev = makeVSCodeWrapper "vscode-dev" lean-dev;
-
-  devShell = mkShell {
-    buildInputs = [ nix ];
-    shellHook = ''
-      export LEAN_SRC_PATH="${srcPath}"
-    '';
-  };
 })

nix/packages.nix

@@ -1,9 +1,6 @@
-{ src, pkgs, nix, ... } @ args:
+{ src, pkgs, ... } @ args:
 with pkgs;
 let
-  nix-pinned = writeShellScriptBin "nix" ''
-    ${nix.packages.${system}.default}/bin/nix --experimental-features 'nix-command flakes' --extra-substituters https://lean4.cachix.org/ --option warn-dirty false "$@"
-  '';
   # https://github.com/NixOS/nixpkgs/issues/130963
   llvmPackages = if stdenv.isDarwin then llvmPackages_11 else llvmPackages_15;
   cc = (ccacheWrapper.override rec {
@@ -42,40 +39,9 @@ let
     inherit (lean) stdenv;
     lean = lean.stage1;
     inherit (lean.stage1) leanc;
-    inherit lean-emacs lean-vscode;
-    nix = nix-pinned;
   }));
-  lean4-mode = emacsPackages.melpaBuild {
-    pname = "lean4-mode";
-    version = "1";
-    commit = "1";
-    src = args.lean4-mode;
-    packageRequires = with pkgs.emacsPackages.melpaPackages; [ dash f flycheck magit-section lsp-mode s ];
-    recipe = pkgs.writeText "recipe" ''
-      (lean4-mode
-       :repo "leanprover/lean4-mode"
-       :fetcher github
-       :files ("*.el" "data"))
-    '';
-  };
-  lean-emacs = emacsWithPackages [ lean4-mode ];
-  # updating might be nicer by building from source from a flake input, but this is good enough for now
-  vscode-lean4 = vscode-utils.extensionFromVscodeMarketplace {
-      name = "lean4";
-      publisher = "leanprover";
-      version = "0.0.63";
-      sha256 = "sha256-kjEex7L0F2P4pMdXi4NIZ1y59ywJVubqDqsoYagZNkI=";
-  };
-  lean-vscode = vscode-with-extensions.override {
-    vscodeExtensions = [ vscode-lean4 ];
-  };
 in {
-  inherit cc lean4-mode buildLeanPackage llvmPackages vscode-lean4;
-  lean = lean.stage1;
-  stage0print-paths = lean.stage1.Lean.print-paths;
-  HEAD-as-stage0 = (lean.stage1.Lean.overrideArgs { srcTarget = "..#stage0-from-input.stage0"; srcArgs = "(--override-input lean-stage0 ..\?rev=$(git rev-parse HEAD) -- -Dinterpreter.prefer_native=false \"$@\")"; });
-  HEAD-as-stage1 = (lean.stage1.Lean.overrideArgs { srcTarget = "..\?rev=$(git rev-parse HEAD)#stage0"; });
-  nix = nix-pinned;
+  inherit cc buildLeanPackage llvmPackages;
   nixpkgs = pkgs;
   ciShell = writeShellScriptBin "ciShell" ''
     set -o pipefail
@@ -83,5 +49,4 @@ in {
     # prefix lines with cumulative and individual execution time
     "$@" |& ts -i "(%.S)]" | ts -s "[%M:%S"
   '';
-  vscode = lean-vscode;
-} // lean.stage1.Lean // lean.stage1 // lean
+} // lean.stage1

releases_drafts/hashmap.md

@@ -0,0 +1,3 @@
+* The `Lean` module has switched from `Lean.HashMap` and `Lean.HashSet` to `Std.HashMap` and `Std.HashSet`. `Lean.HashMap` and `Lean.HashSet` are now deprecated and will be removed in a future release. Users of `Lean` APIs that interact with hash maps, for example `Lean.Environment.const2ModIdx`, might encounter minor breakage due to the following breaking changes from `Lean.HashMap` to `Std.HashMap`:
+    * query functions use the term `get` instead of `find`,
+    * the notation `map[key]` no longer returns an optional value but expects a proof that the key is present in the map instead. The previous behavior is available via the `map[key]?` notation.

releases_drafts/libuv.md

@@ -0,0 +1 @@
+* #4963 [LibUV](https://libuv.org/) is now required to build Lean. This change only affects developers who compile Lean themselves instead of obtaining toolchains via `elan`. We have updated the official build instructions with information on how to obtain LibUV on our supported platforms.

releases_drafts/varCtorNameLint.md

@@ -1,45 +0,0 @@
-A new linter flags situations where a local variable's name is one of
-the argumentless constructors of its type. This can arise when a user either
-doesn't open a namespace or doesn't add a dot or leading qualifier, as
-in the following:
-
-````
-inductive Tree (α : Type) where
-  | leaf
-  | branch (left : Tree α) (val : α) (right : Tree α)
-
-def depth : Tree α → Nat
-  | leaf => 0
-````
-
-With this linter, the `leaf` pattern is highlighted as a local
-variable whose name overlaps with the constructor `Tree.leaf`.
-
-The linter can be disabled with `set_option linter.constructorNameAsVariable false`.
-
-Additionally, the error message that occurs when a name in a pattern that takes arguments isn't valid now suggests similar names that would be valid. This means that the following definition:
-
-```
-def length (list : List α) : Nat :=
-  match list with
-  | nil => 0
-  | cons x xs => length xs + 1
-```
-
-now results in the following warning:
-
-```
-warning: Local variable 'nil' resembles constructor 'List.nil' - write '.nil' (with a dot) or 'List.nil' to use the constructor.
-note: this linter can be disabled with `set_option linter.constructorNameAsVariable false`
-```
-
-and error:
-
-```
-invalid pattern, constructor or constant marked with '[match_pattern]' expected
-
-Suggestion: 'List.cons' is similar
-```
-
-
-#4301

script/prepare-llvm-linux.sh

@@ -38,7 +38,7 @@ $CP $GLIBC/lib/*crt* llvm/lib/
 $CP $GLIBC/lib/*crt* stage1/lib/
 # runtime
 (cd llvm; $CP --parents lib/clang/*/lib/*/{clang_rt.*.o,libclang_rt.builtins*} ../stage1)
-$CP llvm/lib/*/lib{c++,c++abi,unwind}.* $GMP/lib/libgmp.a stage1/lib/
+$CP llvm/lib/*/lib{c++,c++abi,unwind}.* $GMP/lib/libgmp.a $LIBUV/lib/libuv.a stage1/lib/
 # LLVM 15 appears to ship the dependencies in 'llvm/lib/<target-triple>/' and 'llvm/include/<target-triple>/'
 # but clang-15 that we use to compile is linked against 'llvm/lib/' and 'llvm/include'
 # https://github.com/llvm/llvm-project/issues/54955
@@ -62,8 +62,8 @@ 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 -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 -luv -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'"
+echo -n " -DLEAN_EXTRA_LINKER_FLAGS='-Wl,--as-needed -lgmp -luv -Wl,--no-as-needed'"
 # do not set `LEAN_CC` for tests
 echo -n " -DLEAN_TEST_VARS=''"

script/prepare-llvm-macos.sh

@@ -9,6 +9,7 @@ set -uxo pipefail
 # use full LLVM release for compiling C++ code, but subset for compiling C code and distribution
 
 GMP=${GMP:-$(brew --prefix)}
+LIBUV=${LIBUV:-$(brew --prefix)}
 
 [[ -d llvm ]] || (mkdir llvm; gtar xf $1 --strip-components 1 --directory llvm)
 [[ -d llvm-host ]] || if [[ "$#" -gt 1 ]]; then
@@ -46,8 +47,9 @@ echo -n " -DLEAN_EXTRA_CXX_FLAGS='${EXTRA_FLAGS:-}'"
 if [[ -L llvm-host ]]; then
   echo -n " -DCMAKE_C_COMPILER=$PWD/stage1/bin/clang"
   gcp $GMP/lib/libgmp.a stage1/lib/
+  gcp $LIBUV/lib/libuv.a stage1/lib/
   echo -n " -DLEANC_INTERNAL_LINKER_FLAGS='-L ROOT/lib -L ROOT/lib/libc -fuse-ld=lld'"
-  echo -n " -DLEAN_EXTRA_LINKER_FLAGS='-lgmp'"
+  echo -n " -DLEAN_EXTRA_LINKER_FLAGS='-lgmp -luv'"
 else
   echo -n " -DCMAKE_C_COMPILER=$PWD/llvm-host/bin/clang -DLEANC_OPTS='--sysroot $PWD/stage1 -resource-dir $PWD/stage1/lib/clang/15.0.1 ${EXTRA_FLAGS:-}'"
   echo -n " -DLEANC_INTERNAL_LINKER_FLAGS='-L ROOT/lib -L ROOT/lib/libc -fuse-ld=lld'"

script/prepare-llvm-mingw.sh

@@ -31,15 +31,15 @@ cp /clang64/lib/{crtbegin,crtend,crt2,dllcrt2}.o stage1/lib/
 # runtime
 (cd llvm; cp --parents lib/clang/*/lib/*/libclang_rt.builtins* ../stage1)
 # further dependencies
-cp /clang64/lib/lib{m,bcrypt,mingw32,moldname,mingwex,msvcrt,pthread,advapi32,shell32,user32,kernel32,ucrtbase}.* /clang64/lib/libgmp.a llvm/lib/lib{c++,c++abi,unwind}.a stage1/lib/
+cp /clang64/lib/lib{m,bcrypt,mingw32,moldname,mingwex,msvcrt,pthread,advapi32,shell32,user32,kernel32,ucrtbase}.* /clang64/lib/libgmp.a /clang64/lib/libuv.a llvm/lib/lib{c++,c++abi,unwind}.a stage1/lib/
 echo -n " -DLEAN_STANDALONE=ON"
 echo -n " -DCMAKE_C_COMPILER=$PWD/stage1/bin/clang.exe -DCMAKE_C_COMPILER_WORKS=1 -DCMAKE_CXX_COMPILER=$PWD/llvm/bin/clang++.exe -DCMAKE_CXX_COMPILER_WORKS=1 -DLEAN_CXX_STDLIB='-lc++ -lc++abi'"
 echo -n " -DSTAGE0_CMAKE_C_COMPILER=clang -DSTAGE0_CMAKE_CXX_COMPILER=clang++"
 echo -n " -DLEAN_EXTRA_CXX_FLAGS='--sysroot $PWD/llvm -idirafter /clang64/include/'"
 echo -n " -DLEANC_INTERNAL_FLAGS='--sysroot ROOT -nostdinc -isystem ROOT/include/clang' -DLEANC_CC=ROOT/bin/clang.exe"
-echo -n " -DLEANC_INTERNAL_LINKER_FLAGS='-L ROOT/lib -static-libgcc -Wl,-Bstatic -lgmp -lunwind -Wl,-Bdynamic -fuse-ld=lld'"
+echo -n " -DLEANC_INTERNAL_LINKER_FLAGS='-L ROOT/lib -static-libgcc -Wl,-Bstatic -lgmp -luv -lunwind -Wl,-Bdynamic -fuse-ld=lld'"
 # when not using the above flags, link GMP dynamically/as usual
-echo -n " -DLEAN_EXTRA_LINKER_FLAGS='-lgmp -lucrtbase'"
+echo -n " -DLEAN_EXTRA_LINKER_FLAGS='-lgmp -luv -lucrtbase'"
 # do not set `LEAN_CC` for tests
 echo -n " -DAUTO_THREAD_FINALIZATION=OFF -DSTAGE0_AUTO_THREAD_FINALIZATION=OFF"
 echo -n " -DLEAN_TEST_VARS=''"

src/CMakeLists.txt

@@ -1,5 +1,6 @@
 cmake_minimum_required(VERSION 3.10)
 cmake_policy(SET CMP0054 NEW)
+cmake_policy(SET CMP0110 NEW)
 if(NOT (${CMAKE_GENERATOR} MATCHES "Unix Makefiles"))
   message(FATAL_ERROR "The only supported CMake generator at the moment is 'Unix Makefiles'")
 endif()
@@ -9,7 +10,7 @@ endif()
 include(ExternalProject)
 project(LEAN CXX C)
 set(LEAN_VERSION_MAJOR 4)
-set(LEAN_VERSION_MINOR 11)
+set(LEAN_VERSION_MINOR 12)
 set(LEAN_VERSION_PATCH 0)
 set(LEAN_VERSION_IS_RELEASE 0)  # This number is 1 in the release revision, and 0 otherwise.
 set(LEAN_SPECIAL_VERSION_DESC "" CACHE STRING "Additional version description like 'nightly-2018-03-11'")
@@ -242,6 +243,15 @@ if("${USE_GMP}" MATCHES "ON")
   endif()
 endif()
 
+if(NOT "${CMAKE_SYSTEM_NAME}" MATCHES "Emscripten")
+  # LibUV
+  find_package(LibUV 1.0.0 REQUIRED)
+  include_directories(${LIBUV_INCLUDE_DIR})
+endif()
+if(NOT LEAN_STANDALONE)
+  string(APPEND LEAN_EXTRA_LINKER_FLAGS " ${LIBUV_LIBRARIES}")
+endif()
+
 # ccache
 if(CCACHE AND NOT CMAKE_CXX_COMPILER_LAUNCHER AND NOT CMAKE_C_COMPILER_LAUNCHER)
   find_program(CCACHE_PATH ccache)
@@ -372,6 +382,7 @@ if(${CMAKE_SYSTEM_NAME} MATCHES "Linux")
 elseif(${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
   string(APPEND CMAKE_CXX_FLAGS " -ftls-model=initial-exec")
   string(APPEND INIT_SHARED_LINKER_FLAGS " -install_name @rpath/libInit_shared.dylib")
+  string(APPEND LEANSHARED_1_LINKER_FLAGS " -install_name @rpath/libleanshared_1.dylib")
   string(APPEND LEANSHARED_LINKER_FLAGS " -install_name @rpath/libleanshared.dylib")
   string(APPEND CMAKE_EXE_LINKER_FLAGS " -Wl,-rpath,@executable_path/../lib -Wl,-rpath,@executable_path/../lib/lean")
 elseif(${CMAKE_SYSTEM_NAME} MATCHES "Emscripten")
@@ -401,8 +412,8 @@ endif()
 # executable or `leanshared`, plugins would try to look them up at load time (even though they
 # are already loaded) and probably fail unless we set up LD_LIBRARY_PATH.
 if(${CMAKE_SYSTEM_NAME} MATCHES "Windows")
-  # import library created by the `leanshared` target
-  string(APPEND LEANC_SHARED_LINKER_FLAGS " -lInit_shared -lleanshared")
+  # import libraries created by the stdlib.make targets
+  string(APPEND LEANC_SHARED_LINKER_FLAGS " -lInit_shared -lleanshared_1 -lleanshared")
 elseif("${CMAKE_SYSTEM_NAME}" MATCHES "Darwin")
   string(APPEND LEANC_SHARED_LINKER_FLAGS " -Wl,-undefined,dynamic_lookup")
 endif()
@@ -459,6 +470,22 @@ if(CMAKE_OSX_SYSROOT AND NOT LEAN_STANDALONE)
   string(APPEND LEANC_EXTRA_FLAGS " ${CMAKE_CXX_SYSROOT_FLAG}${CMAKE_OSX_SYSROOT}")
 endif()
 
+add_subdirectory(initialize)
+add_subdirectory(shell)
+# to be included in `leanshared` but not the smaller `leanshared_1` (as it would pull
+# in the world)
+add_library(leaninitialize STATIC $<TARGET_OBJECTS:initialize>)
+set_target_properties(leaninitialize PROPERTIES
+  ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib/temp
+  OUTPUT_NAME leaninitialize)
+add_library(leanshell STATIC util/shell.cpp)
+set_target_properties(leanshell PROPERTIES
+  ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib/temp
+  OUTPUT_NAME leanshell)
+if (${CMAKE_SYSTEM_NAME} MATCHES "Windows")
+  string(APPEND CMAKE_EXE_LINKER_FLAGS " -Wl,--whole-archive -lleanmanifest -Wl,--no-whole-archive")
+endif()
+
 if(${STAGE} GREATER 1)
   # reuse C++ parts, which don't change
   add_library(leanrt_initial-exec STATIC IMPORTED)
@@ -467,13 +494,17 @@ if(${STAGE} GREATER 1)
   add_library(leanrt STATIC IMPORTED)
   set_target_properties(leanrt PROPERTIES
     IMPORTED_LOCATION "${CMAKE_BINARY_DIR}/lib/lean/libleanrt.a")
+  add_library(leancpp_1 STATIC IMPORTED)
+  set_target_properties(leancpp_1 PROPERTIES
+    IMPORTED_LOCATION "${CMAKE_BINARY_DIR}/lib/temp/libleancpp_1.a")
   add_library(leancpp STATIC IMPORTED)
   set_target_properties(leancpp PROPERTIES
     IMPORTED_LOCATION "${CMAKE_BINARY_DIR}/lib/lean/libleancpp.a")
   add_custom_target(copy-leancpp
     COMMAND cmake -E copy_if_different "${PREV_STAGE}/runtime/libleanrt_initial-exec.a" "${CMAKE_BINARY_DIR}/runtime/libleanrt_initial-exec.a"
     COMMAND cmake -E copy_if_different "${PREV_STAGE}/lib/lean/libleanrt.a" "${CMAKE_BINARY_DIR}/lib/lean/libleanrt.a"
-    COMMAND cmake -E copy_if_different "${PREV_STAGE}/lib/lean/libleancpp.a" "${CMAKE_BINARY_DIR}/lib/lean/libleancpp.a")
+    COMMAND cmake -E copy_if_different "${PREV_STAGE}/lib/lean/libleancpp.a" "${CMAKE_BINARY_DIR}/lib/lean/libleancpp.a"
+    COMMAND cmake -E copy_if_different "${PREV_STAGE}/lib/temp/libleancpp_1.a" "${CMAKE_BINARY_DIR}/lib/temp/libleancpp_1.a")
   add_dependencies(leancpp copy-leancpp)
   if(LLVM)
       add_custom_target(copy-lean-h-bc
@@ -493,10 +524,13 @@ else()
   set(LEAN_OBJS ${LEAN_OBJS} $<TARGET_OBJECTS:constructions>)
   add_subdirectory(library/compiler)
   set(LEAN_OBJS ${LEAN_OBJS} $<TARGET_OBJECTS:compiler>)
-  add_subdirectory(initialize)
-  set(LEAN_OBJS ${LEAN_OBJS} $<TARGET_OBJECTS:initialize>)
 
-  add_library(leancpp STATIC ${LEAN_OBJS})
+  # leancpp without `initialize` (see `leaninitialize` above)
+  add_library(leancpp_1 STATIC ${LEAN_OBJS})
+  set_target_properties(leancpp_1 PROPERTIES
+    ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib/temp
+    OUTPUT_NAME leancpp_1)
+  add_library(leancpp STATIC ${LEAN_OBJS} $<TARGET_OBJECTS:initialize>)
   set_target_properties(leancpp PROPERTIES
     OUTPUT_NAME leancpp)
 endif()
@@ -508,25 +542,12 @@ string(REGEX REPLACE "^([a-zA-Z]):" "/\\1" LEAN_BIN "${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}/lib/temp/libStd.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,${CMAKE_BINARY_DIR}/lib/lean/libStd.a -Wl,-force_load,${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 -lStd -lLean -lleancpp -Wl,--no-whole-archive ${CMAKE_BINARY_DIR}/runtime/libleanrt_initial-exec.a ${LEANSHARED_LINKER_FLAGS}")
-endif()
-
 if (${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")
+  string(APPEND LEAN_EXE_LINKER_FLAGS " ${LIB}/temp/libleanshell.a ${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
@@ -571,11 +592,11 @@ else()
 
   add_custom_target(leanshared ALL
     WORKING_DIRECTORY ${LEAN_SOURCE_DIR}
-    DEPENDS Init_shared leancpp
+    DEPENDS Init_shared leancpp_1 leancpp leanshell leaninitialize
     COMMAND $(MAKE) -f ${CMAKE_BINARY_DIR}/stdlib.make leanshared
     VERBATIM)
 
-  string(APPEND CMAKE_EXE_LINKER_FLAGS " -lInit_shared -lleanshared")
+  string(APPEND CMAKE_EXE_LINKER_FLAGS " -lInit_shared -lleanshared_1 -lleanshared")
 endif()
 
 if(NOT ${CMAKE_SYSTEM_NAME} MATCHES "Emscripten")
@@ -612,8 +633,6 @@ file(COPY ${LEAN_SOURCE_DIR}/bin/leanmake DESTINATION ${CMAKE_BINARY_DIR}/bin)
 
 install(DIRECTORY "${CMAKE_BINARY_DIR}/bin/" USE_SOURCE_PERMISSIONS DESTINATION bin)
 
-add_subdirectory(shell)
-
 add_custom_target(clean-stdlib
   COMMAND rm -rf "${CMAKE_BINARY_DIR}/lib" || true)
 

src/Init/ByCases.lean

@@ -67,12 +67,8 @@ theorem ite_some_none_eq_none [Decidable P] :
 -- This is not marked as `simp` as it is already handled by `dite_eq_right_iff`.
 theorem dite_some_none_eq_none [Decidable P] {x : P → α} :
     (if h : P then some (x h) else none) = none ↔ ¬P := by
-  simp only [dite_eq_right_iff]
-  rfl
+  simp
 
 @[simp] theorem dite_some_none_eq_some [Decidable P] {x : P → α} {y : α} :
     (if h : P then some (x h) else none) = some y ↔ ∃ h : P, x h = y := by
-  by_cases h : P <;> simp only [h, dite_cond_eq_true, dite_cond_eq_false, Option.some.injEq,
-    false_iff, not_exists]
-  case pos => exact ⟨fun h_eq ↦ Exists.intro h h_eq, fun h_exists => h_exists.2⟩
-  case neg => exact fun h_false _ ↦ h_false
+  by_cases h : P <;> simp [h]

src/Init/Control/ExceptCps.lean

@@ -34,7 +34,7 @@ instance : Monad (ExceptCpsT ε m) where
   bind x f := fun _ k₁ k₂ => x _ (fun a => f a _ k₁ k₂) k₂
 
 instance : LawfulMonad (ExceptCpsT σ m) := by
-  refine' { .. } <;> intros <;> rfl
+  refine LawfulMonad.mk' _ ?_ ?_ ?_ <;> intros <;> rfl
 
 instance : MonadExceptOf ε (ExceptCpsT ε m) where
   throw e  := fun _ _ k => k e

src/Init/Control/Lawful/Basic.lean

@@ -153,7 +153,7 @@ namespace Id
 @[simp] theorem pure_eq (a : α) : (pure a : Id α) = a := rfl
 
 instance : LawfulMonad Id := by
-  refine' { .. } <;> intros <;> rfl
+  refine LawfulMonad.mk' _ ?_ ?_ ?_ <;> intros <;> rfl
 
 end Id
 

src/Init/Control/StateCps.lean

@@ -35,7 +35,7 @@ instance : Monad (StateCpsT σ m) where
   bind x f := fun δ s k => x δ s fun a s => f a δ s k
 
 instance : LawfulMonad (StateCpsT σ m) := by
-  refine' { .. } <;> intros <;> rfl
+  refine LawfulMonad.mk' _ ?_ ?_ ?_ <;> intros <;> rfl
 
 @[always_inline]
 instance : MonadStateOf σ (StateCpsT σ m) where

src/Init/Core.lean

@@ -474,6 +474,8 @@ class LawfulSingleton (α : Type u) (β : Type v) [EmptyCollection β] [Insert
   insert_emptyc_eq (x : α) : (insert x ∅ : β) = singleton x
 export LawfulSingleton (insert_emptyc_eq)
 
+attribute [simp] 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 }`. -/
@@ -701,7 +703,7 @@ 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)
+@[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⟩
 
@@ -754,7 +756,7 @@ noncomputable def HEq.elim {α : Sort u} {a : α} {p : α → Sort v} {b : α} (
 theorem HEq.subst {p : (T : Sort u) → T → Prop} (h₁ : HEq a b) (h₂ : p α a) : p β b :=
   HEq.ndrecOn h₁ h₂
 
-theorem HEq.symm (h : HEq a b) : HEq b a :=
+@[symm] theorem HEq.symm (h : HEq a b) : HEq b a :=
   h.rec (HEq.refl a)
 
 theorem heq_of_eq (h : a = a') : HEq a a' :=
@@ -810,15 +812,15 @@ instance : Trans Iff Iff Iff where
 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.symm (h : a ↔ b) : b ↔ a := Iff.intro h.mpr h.mp
+@[symm] 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.symm : a ∧ b → b ∧ a := fun ⟨ha, hb⟩ => ⟨hb, ha⟩
+@[symm] 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
+@[symm] 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
 
@@ -1102,9 +1104,17 @@ inductive Relation.TransGen {α : Sort u} (r : α → α → Prop) : α → α
 /-- Deprecated synonym for `Relation.TransGen`. -/
 @[deprecated Relation.TransGen (since := "2024-07-16")] abbrev TC := @Relation.TransGen
 
+theorem Relation.TransGen.trans {α : Sort u} {r : α → α → Prop} {a b c} :
+    TransGen r a b → TransGen r b c → TransGen r a c := by
+  intro hab hbc
+  induction hbc with
+  | single h => exact TransGen.tail hab h
+  | tail _ h ih => exact TransGen.tail ih h
+
 /-! # Subtype -/
 
 namespace Subtype
+
 theorem existsOfSubtype {α : Type u} {p : α → Prop} : { x // p x } → Exists (fun x => p x)
   | ⟨a, h⟩ => ⟨a, h⟩
 
@@ -1201,9 +1211,13 @@ def Prod.map {α₁ : Type u₁} {α₂ : Type u₂} {β₁ : Type v₁} {β₂
 
 /-! # Dependent products -/
 
-theorem ex_of_PSigma {α : Type u} {p : α → Prop} : (PSigma (fun x => p x)) → Exists (fun x => p x)
+theorem Exists.of_psigma_prop {α : Sort u} {p : α → Prop} : (PSigma (fun x => p x)) → Exists (fun x => p x)
   | ⟨x, hx⟩ => ⟨x, hx⟩
 
+@[deprecated Exists.of_psigma_prop (since := "2024-07-27")]
+theorem ex_of_PSigma {α : Type u} {p : α → Prop} : (PSigma (fun x => p x)) → Exists (fun x => p x) :=
+  Exists.of_psigma_prop
+
 protected theorem PSigma.eta {α : Sort u} {β : α → Sort v} {a₁ a₂ : α} {b₁ : β a₁} {b₂ : β a₂}
     (h₁ : a₁ = a₂) (h₂ : Eq.ndrec b₁ h₁ = b₂) : PSigma.mk a₁ b₁ = PSigma.mk a₂ b₂ := by
   subst h₁
@@ -1545,7 +1559,7 @@ protected abbrev rec
     (q : Quot r) : motive q :=
   Eq.ndrecOn (Quot.liftIndepPr1 f h q) ((lift (Quot.indep f) (Quot.indepCoherent f h) q).2)
 
-@[inherit_doc Quot.rec] protected abbrev recOn
+@[inherit_doc Quot.rec, elab_as_elim] protected abbrev recOn
     (q : Quot r)
     (f : (a : α) → motive (Quot.mk r a))
     (h : (a b : α) → (p : r a b) → Eq.ndrec (f a) (sound p) = f b)
@@ -1556,7 +1570,7 @@ protected abbrev rec
 Dependent induction principle for a quotient, when the target type is a `Subsingleton`.
 In this case the quotient's side condition is trivial so any function can be lifted.
 -/
-protected abbrev recOnSubsingleton
+@[elab_as_elim] protected abbrev recOnSubsingleton
     [h : (a : α) → Subsingleton (motive (Quot.mk r a))]
     (q : Quot r)
     (f : (a : α) → motive (Quot.mk r a))

src/Init/Data.lean

@@ -36,3 +36,4 @@ import Init.Data.Channel
 import Init.Data.Cast
 import Init.Data.Sum
 import Init.Data.BEq
+import Init.Data.Subtype

src/Init/Data/AC.lean

@@ -6,7 +6,7 @@ Authors: Dany Fabian
 
 prelude
 import Init.Classical
-import Init.Data.List
+import Init.ByCases
 
 namespace Lean.Data.AC
 inductive Expr

src/Init/Data/Array/Basic.lean

@@ -50,6 +50,13 @@ instance : Inhabited (Array α) where
 def singleton (v : α) : Array α :=
   mkArray 1 v
 
+/-- Low-level version of `size` that directly queries the C array object cached size.
+    While this is not provable, `usize` always returns the exact size of the array since
+    the implementation only supports arrays of size less than `USize.size`.
+-/
+@[extern "lean_array_size", simp]
+def usize (a : @& Array α) : USize := a.size.toUSize
+
 /-- Low-level version of `fget` which is as fast as a C array read.
    `Fin` values are represented as tag pointers in the Lean runtime. Thus,
    `fget` may be slightly slower than `uget`. -/
@@ -101,7 +108,7 @@ def swap (a : Array α) (i j : @& Fin a.size) : Array α :=
   a'.set (size_set a i v₂ ▸ j) v₁
 
 /--
-Swaps two entries in an array, or panics if either index is out of bounds.
+Swaps two entries in an array, or returns the array unchanged if either index is out of bounds.
 
 This will perform the update destructively provided that `a` has a reference
 count of 1 when called.
@@ -174,7 +181,7 @@ def modifyOp (self : Array α) (idx : Nat) (f : α → α) : Array α :=
 
   This kind of low level trick can be removed with a little bit of compiler support. For example, if the compiler simplifies `as.size < usizeSz` to true. -/
 @[inline] unsafe def forInUnsafe {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m] (as : Array α) (b : β) (f : α → β → m (ForInStep β)) : m β :=
-  let sz := USize.ofNat as.size
+  let sz := as.usize
   let rec @[specialize] loop (i : USize) (b : β) : m β := do
     if i < sz then
       let a := as.uget i lcProof
@@ -280,7 +287,7 @@ def foldrM {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m] (f : α
 /-- See comment at `forInUnsafe` -/
 @[inline]
 unsafe def mapMUnsafe {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m] (f : α → m β) (as : Array α) : m (Array β) :=
-  let sz := USize.ofNat as.size
+  let sz := as.usize
   let rec @[specialize] map (i : USize) (r : Array NonScalar) : m (Array PNonScalar.{v}) := do
     if i < sz then
      let v    := r.uget i lcProof

src/Init/Data/Array/Lemmas.lean

@@ -6,7 +6,8 @@ Authors: Mario Carneiro
 prelude
 import Init.Data.Nat.MinMax
 import Init.Data.Nat.Lemmas
-import Init.Data.List.Lemmas
+import Init.Data.List.Monadic
+import Init.Data.List.Nat.Range
 import Init.Data.Fin.Basic
 import Init.Data.Array.Mem
 import Init.TacticsExtra
@@ -334,8 +335,19 @@ theorem mem_data {a : α} {l : Array α} : a ∈ l.data ↔ a ∈ l := (mem_def
 
 theorem not_mem_nil (a : α) : ¬ a ∈ #[] := nofun
 
+theorem getElem_of_mem {a : α} {as : Array α} :
+    a ∈ as → (∃ (n : Nat) (h : n < as.size), as[n]'h = a) := by
+  intro ha
+  rcases List.getElem_of_mem ha.val with ⟨i, hbound, hi⟩
+  exists i
+  exists hbound
+
 /-- # get lemmas -/
 
+theorem lt_of_getElem {x : α} {a : Array α} {idx : Nat} {hidx : idx < a.size} (_ : a[idx] = x) :
+    idx < a.size :=
+  hidx
+
 theorem getElem?_mem {l : Array α} {i : Fin l.size} : l[i] ∈ l := by
   erw [Array.mem_def, getElem_eq_data_getElem]
   apply List.get_mem
@@ -505,6 +517,13 @@ theorem size_eq_length_data (as : Array α) : as.size = as.data.length := rfl
     simp only [mkEmpty_eq, size_push] at *
     omega
 
+@[simp] theorem data_range (n : Nat) : (range n).data = List.range n := by
+  induction n <;> simp_all [range, Nat.fold, flip, List.range_succ]
+
+@[simp]
+theorem getElem_range {n : Nat} {x : Nat} (h : x < (Array.range n).size) : (Array.range n)[x] = x := by
+  simp [getElem_eq_data_getElem]
+
 set_option linter.deprecated false in
 @[simp] theorem reverse_data (a : Array α) : a.reverse.data = a.data.reverse := by
   let rec go (as : Array α) (i j hj)
@@ -707,12 +726,27 @@ theorem mapIdx_spec (as : Array α) (f : Fin as.size → α → β)
   unfold modify modifyM Id.run
   split <;> simp
 
+theorem getElem_modify {as : Array α} {x i} (h : i < as.size) :
+    (as.modify x f)[i]'(by simp [h]) = if x = i then f as[i] else as[i] := by
+  simp only [modify, modifyM, get_eq_getElem, Id.run, Id.pure_eq]
+  split
+  · simp only [Id.bind_eq, get_set _ _ _ h]; split <;> simp [*]
+  · rw [if_neg (mt (by rintro rfl; exact h) ‹_›)]
+
+theorem getElem_modify_self {as : Array α} {i : Nat} (h : i < as.size) (f : α → α) :
+    (as.modify i f)[i]'(by simp [h]) = f as[i] := by
+  simp [getElem_modify h]
+
+theorem getElem_modify_of_ne {as : Array α} {i : Nat} (hj : j < as.size)
+    (f : α → α) (h : i ≠ j) :
+    (as.modify i f)[j]'(by rwa [size_modify]) = as[j] := by
+  simp [getElem_modify hj, h]
+
+@[deprecated getElem_modify (since := "2024-08-08")]
 theorem get_modify {arr : Array α} {x i} (h : i < arr.size) :
     (arr.modify x f).get ⟨i, by simp [h]⟩ =
     if x = i then f (arr.get ⟨i, h⟩) else arr.get ⟨i, h⟩ := by
-  simp [modify, modifyM, Id.run]; split
-  · simp [get_set _ _ _ h]; split <;> simp [*]
-  · rw [if_neg (mt (by rintro rfl; exact h) ‹_›)]
+  simp [getElem_modify h]
 
 /-! ### filter -/
 

src/Init/Data/Array/Mem.lean

@@ -38,8 +38,8 @@ macro "array_get_dec" : tactic =>
     -- subsumed by simp
     -- | with_reducible apply sizeOf_get
     -- | with_reducible apply sizeOf_getElem
-    | (with_reducible apply Nat.lt_trans (sizeOf_get ..)); simp_arith
-    | (with_reducible apply Nat.lt_trans (sizeOf_getElem ..)); simp_arith
+    | (with_reducible apply Nat.lt_of_lt_of_le (sizeOf_get ..)); simp_arith
+    | (with_reducible apply Nat.lt_of_lt_of_le (sizeOf_getElem ..)); simp_arith
     )
 
 macro_rules | `(tactic| decreasing_trivial) => `(tactic| array_get_dec)
@@ -52,7 +52,7 @@ macro "array_mem_dec" : tactic =>
   `(tactic| first
     | with_reducible apply Array.sizeOf_lt_of_mem; assumption; done
     | with_reducible
-        apply Nat.lt_trans (Array.sizeOf_lt_of_mem ?h)
+        apply Nat.lt_of_lt_of_le (Array.sizeOf_lt_of_mem ?h)
         case' h => assumption
       simp_arith)
 

src/Init/Data/Array/TakeDrop.lean

@@ -5,7 +5,7 @@ Authors: Markus Himmel
 -/
 prelude
 import Init.Data.Array.Lemmas
-import Init.Data.List.TakeDrop
+import Init.Data.List.Nat.TakeDrop
 
 namespace Array
 

src/Init/Data/BitVec/Basic.lean

@@ -20,6 +20,8 @@ We define many of the bitvector operations from the
 of SMT-LIBv2.
 -/
 
+set_option linter.missingDocs true
+
 /--
 A bitvector of the specified width.
 
@@ -34,14 +36,14 @@ structure BitVec (w : Nat) where
   O(1), because we use `Fin` as the internal representation of a bitvector. -/
   toFin : Fin (2^w)
 
-@[deprecated (since := "2024-04-12")]
-protected abbrev Std.BitVec := _root_.BitVec
-
+/--
+Bitvectors have decidable equality. This should be used via the instance `DecidableEq (BitVec n)`.
+-/
 -- 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
+def BitVec.decEq (x y : BitVec n) : Decidable (x = y) :=
+  match x, y with
   | ⟨n⟩, ⟨m⟩ =>
     if h : n = m then
       isTrue (h ▸ rfl)
@@ -67,9 +69,9 @@ protected def ofNat (n : Nat) (i : Nat) : BitVec n where
 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
+/-- Given a bitvector `x`, 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
+protected def toNat (x : BitVec n) : Nat := x.toFin.val
 
 /-- Return the bound in terms of toNat. -/
 theorem isLt (x : BitVec w) : x.toNat < 2^w := x.toFin.isLt
@@ -121,18 +123,18 @@ section getXsb
 @[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
+@[inline] protected def msb (x : BitVec n) : Bool := getMsb x 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
+protected def toInt (x : BitVec n) : Int :=
+  if 2 * x.toNat < 2^n then
+    x.toNat
   else
-    (a.toNat : Int) - (2^n : Nat)
+    (x.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
@@ -213,7 +215,7 @@ 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
+protected def abs (x : BitVec n) : BitVec n := if x.msb then .neg x else x
 
 /--
 Multiplication for bit vectors. This can be interpreted as either signed or unsigned negation
@@ -260,12 +262,12 @@ 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)
+def sdiv (x y : BitVec n) : BitVec n :=
+  match x.msb, y.msb with
+  | false, false => udiv x y
+  | false, true  => .neg (udiv x (.neg y))
+  | true,  false => .neg (udiv (.neg x) y)
+  | true,  true  => udiv (.neg x) (.neg y)
 
 /--
 Signed division for bit vectors using SMTLIB rules for division by zero.
@@ -274,40 +276,40 @@ 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)
+def smtSDiv (x y : BitVec n) : BitVec n :=
+  match x.msb, y.msb with
+  | false, false => smtUDiv x y
+  | false, true  => .neg (smtUDiv x (.neg y))
+  | true,  false => .neg (smtUDiv (.neg x) y)
+  | true,  true  => smtUDiv (.neg x) (.neg y)
 
 /--
 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))
+def srem (x y : BitVec n) : BitVec n :=
+  match x.msb, y.msb with
+  | false, false => umod x y
+  | false, true  => umod x (.neg y)
+  | true,  false => .neg (umod (.neg x) y)
+  | true,  true  => .neg (umod (.neg x) (.neg y))
 
 /--
 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
+def smod (x y : BitVec m) : BitVec m :=
+  match x.msb, y.msb with
+  | false, false => umod x y
   | false, true =>
-    let u := umod s (.neg t)
-    (if u = .zero m then u else .add u t)
+    let u := umod x (.neg y)
+    (if u = .zero m then u else .add u y)
   | 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))
+    let u := umod (.neg x) y
+    (if u = .zero m then u else .sub y u)
+  | true, true => .neg (umod (.neg x) (.neg y))
 
 end arithmetic
 
@@ -371,8 +373,8 @@ 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)
+/-- `cast eq x` embeds `x` into an equal `BitVec` type. -/
+@[inline] def cast (eq : n = m) (x : BitVec n) : BitVec m := .ofNatLt x.toNat (eq ▸ x.isLt)
 
 @[simp] theorem cast_ofNat {n m : Nat} (h : n = m) (x : Nat) :
     cast h (BitVec.ofNat n x) = BitVec.ofNat m x := by
@@ -389,7 +391,7 @@ Extraction of bits `start` to `start + len - 1` from a bit vector of size `n` to
 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)
+def extractLsb' (start len : Nat) (x : BitVec n) : BitVec len := .ofNat _ (x.toNat >>> start)
 
 /--
 Extraction of bits `hi` (inclusive) down to `lo` (inclusive) from a bit vector of size `n` to
@@ -397,12 +399,12 @@ 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
+def extractLsb (hi lo : Nat) (x : BitVec n) : BitVec (hi - lo + 1) := extractLsb' lo _ x
 
 /--
 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 :=
+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)
@@ -411,8 +413,8 @@ def zeroExtend' {n w : Nat} (le : n ≤ w) (x : BitVec n)  : BitVec w :=
 `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
+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)
@@ -500,24 +502,24 @@ 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`.
+equivalent to `x * 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 := BitVec.ofNat n (a.toNat <<< s)
+protected def shiftLeft (x : BitVec n) (s : Nat) : BitVec n := BitVec.ofNat n (x.toNat <<< s)
 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.
+As a numeric operation, this is equivalent to `x / 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
+def ushiftRight (x : BitVec n) (s : Nat) : BitVec n :=
+  (x.toNat >>> s)#'(by
+  let ⟨x, lt⟩ := x
   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]
+  rw [←Nat.mul_one x]
   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⟩
@@ -525,15 +527,24 @@ 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`.
+As a numeric operation, this is equivalent to `x.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)
+def sshiftRight (x : BitVec n) (s : Nat) : BitVec n := .ofInt n (x.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⟩
 
+/--
+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.toNat`.
+
+SMT-Lib name: `bvashr`.
+-/
+def sshiftRight' (a : BitVec n) (s : BitVec m) : BitVec n := a.sshiftRight s.toNat
+
 /-- Auxiliary function for `rotateLeft`, which does not take into account the case where
 the rotation amount is greater than the bitvector width. -/
 def rotateLeftAux (x : BitVec w) (n : Nat) : BitVec w :=
@@ -583,11 +594,9 @@ 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
+  | 0,   _ => 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)
+    (x ++ replicate n x).cast (by rw [Nat.mul_succ]; omega)
 
 /-!
 ### Cons and Concat

src/Init/Data/BitVec/Bitblast.lean

@@ -28,6 +28,8 @@ https://github.com/mhk119/lean-smt/blob/bitvec/Smt/Data/Bitwise.lean.
 
 -/
 
+set_option linter.missingDocs true
+
 open Nat Bool
 
 namespace Bool
@@ -98,6 +100,37 @@ theorem carry_succ (i : Nat) (x y : BitVec w) (c : Bool) :
     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)
 
+/--
+If `x &&& y = 0`, then the carry bit `(x + y + 0)` is always `false` for any index `i`.
+Intuitively, this is because a carry is only produced when at least two of `x`, `y`, and the
+previous carry are true. However, since `x &&& y = 0`, at most one of `x, y` can be true,
+and thus we never have a previous carry, which means that the sum cannot produce a carry.
+-/
+theorem carry_of_and_eq_zero {x y : BitVec w} (h : x &&& y = 0#w) : carry i x y false = false := by
+  induction i with
+  | zero => simp
+  | succ i ih =>
+    replace h := congrArg (·.getLsb i) h
+    simp_all [carry_succ]
+
+/-- The final carry bit when computing `x + y + c` is `true` iff `x.toNat + y.toNat + c.toNat ≥ 2^w`. -/
+theorem carry_width {x y : BitVec w} :
+    carry w x y c = decide (x.toNat + y.toNat + c.toNat ≥ 2^w) := by
+  simp [carry]
+
+/--
+If `x &&& y = 0`, then addition does not overflow, and thus `(x + y).toNat = x.toNat + y.toNat`.
+-/
+theorem toNat_add_of_and_eq_zero {x y : BitVec w} (h : x &&& y = 0#w) :
+    (x + y).toNat = x.toNat + y.toNat := by
+  rw [toNat_add]
+  apply Nat.mod_eq_of_lt
+  suffices ¬ decide (x.toNat + y.toNat + false.toNat ≥ 2^w) by
+    simp only [decide_eq_true_eq] at this
+    omega
+  rw [← carry_width]
+  simp [not_eq_true, carry_of_and_eq_zero h]
+
 /-- Carry function for bitwise addition. -/
 def adcb (x y c : Bool) : Bool × Bool := (atLeastTwo x y c, Bool.xor x (Bool.xor y c))
 
@@ -256,18 +289,18 @@ theorem sle_eq_carry (x y : BitVec w) :
 A recurrence that describes multiplication as repeated addition.
 Is useful for bitblasting multiplication.
 -/
-def mulRec (l r : BitVec w) (s : Nat) : BitVec w :=
-  let cur := if r.getLsb s then (l <<< s) else 0
+def mulRec (x y : BitVec w) (s : Nat) : BitVec w :=
+  let cur := if y.getLsb s then (x <<< s) else 0
   match s with
   | 0 => cur
-  | s + 1 => mulRec l r s + cur
+  | s + 1 => mulRec x y s + cur
 
-theorem mulRec_zero_eq (l r : BitVec w) :
-    mulRec l r 0 = if r.getLsb 0 then l else 0 := by
+theorem mulRec_zero_eq (x y : BitVec w) :
+    mulRec x y 0 = if y.getLsb 0 then x else 0 := by
   simp [mulRec]
 
-theorem mulRec_succ_eq (l r : BitVec w) (s : Nat) :
-    mulRec l r (s + 1) = mulRec l r s + if r.getLsb (s + 1) then (l <<< (s + 1)) else 0 := rfl
+theorem mulRec_succ_eq (x y : BitVec w) (s : Nat) :
+    mulRec x y (s + 1) = mulRec x y s + if y.getLsb (s + 1) then (x <<< (s + 1)) else 0 := rfl
 
 /--
 Recurrence lemma: truncating to `i+1` bits and then zero extending to `w`
@@ -290,32 +323,32 @@ theorem zeroExtend_truncate_succ_eq_zeroExtend_truncate_add_twoPow (x : BitVec w
         simp [hik', hik'']
   · ext k
     simp
-    omega
+    by_cases hi : x.getLsb i <;> simp [hi] <;> omega
 
 /--
-Recurrence lemma: multiplying `l` with the first `s` bits of `r` is the
-same as truncating `r` to `s` bits, then zero extending to the original length,
+Recurrence lemma: multiplying `x` with the first `s` bits of `y` is the
+same as truncating `y` to `s` bits, then zero extending to the original length,
 and performing the multplication. -/
-theorem mulRec_eq_mul_signExtend_truncate (l r : BitVec w) (s : Nat) :
-    mulRec l r s = l * ((r.truncate (s + 1)).zeroExtend w) := by
+theorem mulRec_eq_mul_signExtend_truncate (x y : BitVec w) (s : Nat) :
+    mulRec x y s = x * ((y.truncate (s + 1)).zeroExtend w) := by
   induction s
   case zero =>
     simp only [mulRec_zero_eq, ofNat_eq_ofNat, Nat.reduceAdd]
-    by_cases r.getLsb 0
-    case pos hr =>
-      simp only [hr, ↓reduceIte, truncate, zeroExtend_one_eq_ofBool_getLsb_zero,
-        hr, ofBool_true, ofNat_eq_ofNat]
+    by_cases y.getLsb 0
+    case pos hy =>
+      simp only [hy, ↓reduceIte, truncate, zeroExtend_one_eq_ofBool_getLsb_zero,
+        ofBool_true, ofNat_eq_ofNat]
       rw [zeroExtend_ofNat_one_eq_ofNat_one_of_lt (by omega)]
       simp
-    case neg hr =>
-      simp [hr, zeroExtend_one_eq_ofBool_getLsb_zero]
+    case neg hy =>
+      simp [hy, zeroExtend_one_eq_ofBool_getLsb_zero]
   case succ s' hs =>
     rw [mulRec_succ_eq, hs]
     have heq :
-      (if r.getLsb (s' + 1) = true then l <<< (s' + 1) else 0) =
-        (l * (r &&& (BitVec.twoPow w (s' + 1)))) := by
-      simp only [ofNat_eq_ofNat, and_twoPow_eq]
-      by_cases hr : r.getLsb (s' + 1) <;> simp [hr]
+      (if y.getLsb (s' + 1) = true then x <<< (s' + 1) else 0) =
+        (x * (y &&& (BitVec.twoPow w (s' + 1)))) := by
+      simp only [ofNat_eq_ofNat, and_twoPow]
+      by_cases hy : y.getLsb (s' + 1) <;> simp [hy]
     rw [heq, ← BitVec.mul_add, ← zeroExtend_truncate_succ_eq_zeroExtend_truncate_add_twoPow]
 
 theorem getLsb_mul (x y : BitVec w) (i : Nat) :
@@ -326,4 +359,198 @@ theorem getLsb_mul (x y : BitVec w) (i : Nat) :
   · simp
   · omega
 
+/-! ## shiftLeft recurrence for bitblasting -/
+
+/--
+`shiftLeftRec x y n` shifts `x` to the left by the first `n` bits of `y`.
+
+The theorem `shiftLeft_eq_shiftLeftRec` proves the equivalence of `(x <<< y)` and `shiftLeftRec`.
+
+Together with equations `shiftLeftRec_zero`, `shiftLeftRec_succ`,
+this allows us to unfold `shiftLeft` into a circuit for bitblasting.
+ -/
+def shiftLeftRec (x : BitVec w₁) (y : BitVec w₂) (n : Nat) : BitVec w₁ :=
+  let shiftAmt := (y &&& (twoPow w₂ n))
+  match n with
+  | 0 => x <<< shiftAmt
+  | n + 1 => (shiftLeftRec x y n) <<< shiftAmt
+
+@[simp]
+theorem shiftLeftRec_zero {x : BitVec w₁} {y : BitVec w₂} :
+    shiftLeftRec x y 0 = x <<< (y &&& twoPow w₂ 0)  := by
+  simp [shiftLeftRec]
+
+@[simp]
+theorem shiftLeftRec_succ {x : BitVec w₁} {y : BitVec w₂} :
+    shiftLeftRec x y (n + 1) = (shiftLeftRec x y n) <<< (y &&& twoPow w₂ (n + 1)) := by
+  simp [shiftLeftRec]
+
+/--
+If `y &&& z = 0`, `x <<< (y ||| z) = x <<< y <<< z`.
+This follows as `y &&& z = 0` implies `y ||| z = y + z`,
+and thus `x <<< (y ||| z) = x <<< (y + z) = x <<< y <<< z`.
+-/
+theorem shiftLeft_or_of_and_eq_zero {x : BitVec w₁} {y z : BitVec w₂}
+    (h : y &&& z = 0#w₂) :
+    x <<< (y ||| z) = x <<< y <<< z := by
+  rw [← add_eq_or_of_and_eq_zero _ _ h,
+    shiftLeft_eq', toNat_add_of_and_eq_zero h]
+  simp [shiftLeft_add]
+
+/--
+`shiftLeftRec x y n` shifts `x` to the left by the first `n` bits of `y`.
+-/
+theorem shiftLeftRec_eq {x : BitVec w₁} {y : BitVec w₂} {n : Nat} :
+    shiftLeftRec x y n = x <<< (y.truncate (n + 1)).zeroExtend w₂ := by
+  induction n generalizing x y
+  case zero =>
+    ext i
+    simp only [shiftLeftRec_zero, twoPow_zero, Nat.reduceAdd, truncate_one,
+      and_one_eq_zeroExtend_ofBool_getLsb]
+  case succ n ih =>
+    simp only [shiftLeftRec_succ, and_twoPow]
+    rw [ih]
+    by_cases h : y.getLsb (n + 1)
+    · simp only [h, ↓reduceIte]
+      rw [zeroExtend_truncate_succ_eq_zeroExtend_truncate_or_twoPow_of_getLsb_true h,
+        shiftLeft_or_of_and_eq_zero]
+      simp
+    · simp only [h, false_eq_true, ↓reduceIte, shiftLeft_zero']
+      rw [zeroExtend_truncate_succ_eq_zeroExtend_truncate_of_getLsb_false (i := n + 1)]
+      simp [h]
+
+/--
+Show that `x <<< y` can be written in terms of `shiftLeftRec`.
+This can be unfolded in terms of `shiftLeftRec_zero`, `shiftLeftRec_succ` for bitblasting.
+-/
+theorem shiftLeft_eq_shiftLeftRec (x : BitVec w₁) (y : BitVec w₂) :
+    x <<< y = shiftLeftRec x y (w₂ - 1) := by
+  rcases w₂ with rfl | w₂
+  · simp [of_length_zero]
+  · simp [shiftLeftRec_eq]
+
+/- ### Arithmetic shift right (sshiftRight) recurrence -/
+
+/--
+`sshiftRightRec x y n` shifts `x` arithmetically/signed to the right by the first `n` bits of `y`.
+The theorem `sshiftRight_eq_sshiftRightRec` proves the equivalence of `(x.sshiftRight y)` and `sshiftRightRec`.
+Together with equations `sshiftRightRec_zero`, `sshiftRightRec_succ`,
+this allows us to unfold `sshiftRight` into a circuit for bitblasting.
+-/
+def sshiftRightRec (x : BitVec w₁) (y : BitVec w₂) (n : Nat) : BitVec w₁ :=
+  let shiftAmt := (y &&& (twoPow w₂ n))
+  match n with
+  | 0 => x.sshiftRight' shiftAmt
+  | n + 1 => (sshiftRightRec x y n).sshiftRight' shiftAmt
+
+@[simp]
+theorem sshiftRightRec_zero_eq (x : BitVec w₁) (y : BitVec w₂) :
+    sshiftRightRec x y 0 = x.sshiftRight' (y &&& 1#w₂) := by
+  simp only [sshiftRightRec, twoPow_zero]
+
+@[simp]
+theorem sshiftRightRec_succ_eq (x : BitVec w₁) (y : BitVec w₂) (n : Nat) :
+    sshiftRightRec x y (n + 1) = (sshiftRightRec x y n).sshiftRight' (y &&& twoPow w₂ (n + 1)) := by
+  simp [sshiftRightRec]
+
+/--
+If `y &&& z = 0`, `x.sshiftRight (y ||| z) = (x.sshiftRight y).sshiftRight z`.
+This follows as `y &&& z = 0` implies `y ||| z = y + z`,
+and thus `x.sshiftRight (y ||| z) = x.sshiftRight (y + z) = (x.sshiftRight y).sshiftRight z`.
+-/
+theorem sshiftRight'_or_of_and_eq_zero {x : BitVec w₁} {y z : BitVec w₂}
+    (h : y &&& z = 0#w₂) :
+    x.sshiftRight' (y ||| z) = (x.sshiftRight' y).sshiftRight' z := by
+  simp [sshiftRight', ← add_eq_or_of_and_eq_zero _ _ h,
+    toNat_add_of_and_eq_zero h, sshiftRight_add]
+
+theorem sshiftRightRec_eq (x : BitVec w₁) (y : BitVec w₂) (n : Nat) :
+    sshiftRightRec x y n = x.sshiftRight' ((y.truncate (n + 1)).zeroExtend w₂) := by
+  induction n generalizing x y
+  case zero =>
+    ext i
+    simp [twoPow_zero, Nat.reduceAdd, and_one_eq_zeroExtend_ofBool_getLsb, truncate_one]
+  case succ n ih =>
+    simp only [sshiftRightRec_succ_eq, and_twoPow, ih]
+    by_cases h : y.getLsb (n + 1)
+    · rw [zeroExtend_truncate_succ_eq_zeroExtend_truncate_or_twoPow_of_getLsb_true h,
+        sshiftRight'_or_of_and_eq_zero (by simp), h]
+      simp
+    · rw [zeroExtend_truncate_succ_eq_zeroExtend_truncate_of_getLsb_false (i := n + 1)
+        (by simp [h])]
+      simp [h]
+
+/--
+Show that `x.sshiftRight y` can be written in terms of `sshiftRightRec`.
+This can be unfolded in terms of `sshiftRightRec_zero_eq`, `sshiftRightRec_succ_eq` for bitblasting.
+-/
+theorem sshiftRight_eq_sshiftRightRec (x : BitVec w₁) (y : BitVec w₂) :
+    (x.sshiftRight' y).getLsb i = (sshiftRightRec x y (w₂ - 1)).getLsb i := by
+  rcases w₂ with rfl | w₂
+  · simp [of_length_zero]
+  · simp [sshiftRightRec_eq]
+
+/- ### Logical shift right (ushiftRight) recurrence for bitblasting -/
+
+/--
+`ushiftRightRec x y n` shifts `x` logically to the right by the first `n` bits of `y`.
+
+The theorem `shiftRight_eq_ushiftRightRec` proves the equivalence
+of `(x >>> y)` and `ushiftRightRec`.
+
+Together with equations `ushiftRightRec_zero`, `ushiftRightRec_succ`,
+this allows us to unfold `ushiftRight` into a circuit for bitblasting.
+-/
+def ushiftRightRec (x : BitVec w₁) (y : BitVec w₂) (n : Nat) : BitVec w₁ :=
+  let shiftAmt := (y &&& (twoPow w₂ n))
+  match n with
+  | 0 => x >>> shiftAmt
+  | n + 1 => (ushiftRightRec x y n) >>> shiftAmt
+
+@[simp]
+theorem ushiftRightRec_zero (x : BitVec w₁) (y : BitVec w₂) :
+    ushiftRightRec x y 0 = x >>> (y &&& twoPow w₂ 0) := by
+  simp [ushiftRightRec]
+
+@[simp]
+theorem ushiftRightRec_succ (x : BitVec w₁) (y : BitVec w₂) :
+    ushiftRightRec x y (n + 1) = (ushiftRightRec x y n) >>> (y &&& twoPow w₂ (n + 1)) := by
+  simp [ushiftRightRec]
+
+/--
+If `y &&& z = 0`, `x >>> (y ||| z) = x >>> y >>> z`.
+This follows as `y &&& z = 0` implies `y ||| z = y + z`,
+and thus `x >>> (y ||| z) = x >>> (y + z) = x >>> y >>> z`.
+-/
+theorem ushiftRight'_or_of_and_eq_zero {x : BitVec w₁} {y z : BitVec w₂}
+    (h : y &&& z = 0#w₂) :
+    x >>> (y ||| z) = x >>> y >>> z := by
+  simp [← add_eq_or_of_and_eq_zero _ _ h, toNat_add_of_and_eq_zero h, shiftRight_add]
+
+theorem ushiftRightRec_eq (x : BitVec w₁) (y : BitVec w₂) (n : Nat) :
+    ushiftRightRec x y n = x >>> (y.truncate (n + 1)).zeroExtend w₂ := by
+  induction n generalizing x y
+  case zero =>
+    ext i
+    simp only [ushiftRightRec_zero, twoPow_zero, Nat.reduceAdd,
+      and_one_eq_zeroExtend_ofBool_getLsb, truncate_one]
+  case succ n ih =>
+    simp only [ushiftRightRec_succ, and_twoPow]
+    rw [ih]
+    by_cases h : y.getLsb (n + 1) <;> simp only [h, ↓reduceIte]
+    · rw [zeroExtend_truncate_succ_eq_zeroExtend_truncate_or_twoPow_of_getLsb_true h,
+        ushiftRight'_or_of_and_eq_zero]
+      simp
+    · simp [zeroExtend_truncate_succ_eq_zeroExtend_truncate_of_getLsb_false, h]
+
+/--
+Show that `x >>> y` can be written in terms of `ushiftRightRec`.
+This can be unfolded in terms of `ushiftRightRec_zero`, `ushiftRightRec_succ` for bitblasting.
+-/
+theorem shiftRight_eq_ushiftRightRec (x : BitVec w₁) (y : BitVec w₂) :
+    x >>> y = ushiftRightRec x y (w₂ - 1) := by
+  rcases w₂ with rfl | w₂
+  · simp [of_length_zero]
+  · simp [ushiftRightRec_eq]
+
 end BitVec

src/Init/Data/BitVec/Folds.lean

@@ -8,6 +8,8 @@ import Init.Data.BitVec.Lemmas
 import Init.Data.Nat.Lemmas
 import Init.Data.Fin.Iterate
 
+set_option linter.missingDocs true
+
 namespace BitVec
 
 /--

src/Init/Data/BitVec/Lemmas.lean

@@ -12,6 +12,8 @@ import Init.Data.Nat.Lemmas
 import Init.Data.Nat.Mod
 import Init.Data.Int.Bitwise.Lemmas
 
+set_option linter.missingDocs true
+
 namespace BitVec
 
 /--
@@ -21,7 +23,7 @@ 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
+theorem eq_of_toNat_eq {n} : ∀ {x y : BitVec n}, x.toNat = y.toNat → x = y
   | ⟨_, _⟩, ⟨_, _⟩, rfl => rfl
 
 @[simp] theorem val_toFin (x : BitVec w) : x.toFin.val = x.toNat := rfl
@@ -160,6 +162,16 @@ theorem toNat_zero (n : Nat) : (0#n).toNat = 0 := by trivial
 @[simp] theorem toNat_mod_cancel (x : BitVec n) : x.toNat % (2^n) = x.toNat :=
   Nat.mod_eq_of_lt x.isLt
 
+@[simp] theorem sub_toNat_mod_cancel {x : BitVec w} (h : ¬ x = 0#w) :
+    (2 ^ w - x.toNat) % 2 ^ w = 2 ^ w - x.toNat := by
+  simp only [toNat_eq, toNat_ofNat, Nat.zero_mod] at h
+  rw [Nat.mod_eq_of_lt (by omega)]
+
+@[simp] theorem sub_sub_toNat_cancel {x : BitVec w} :
+    2 ^ w - (2 ^ w - x.toNat) = x.toNat := by
+  simp [Nat.sub_sub_eq_min, Nat.min_eq_right]
+  omega
+
 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)
 
@@ -226,12 +238,12 @@ theorem toNat_ge_of_msb_true {x : BitVec n} (p : BitVec.msb x = true) : x.toNat
 /-! ### 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)
+theorem toInt_eq_toNat_cond (x : BitVec n) :
+    x.toInt =
+      if 2*x.toNat < 2^n then
+        (x.toNat : Int)
       else
-        (i.toNat : Int) - (2^n : Nat) :=
+        (x.toNat : Int) - (2^n : Nat) :=
   rfl
 
 theorem msb_eq_false_iff_two_mul_lt (x : BitVec w) : x.msb = false ↔ 2 * x.toNat < 2^w := by
@@ -258,13 +270,13 @@ theorem toInt_eq_toNat_bmod (x : BitVec n) : x.toInt = Int.bmod x.toNat (2^n) :=
     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
+theorem eq_of_toInt_eq {x y : BitVec n} : x.toInt = y.toInt → x = y := 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
+  have _xlt := x.isLt
+  have _ylt := y.isLt
   split <;> split <;> omega
 
 theorem toInt_inj (x y : BitVec n) : x.toInt = y.toInt ↔ x = y :=
@@ -298,8 +310,7 @@ theorem truncate_eq_zeroExtend {v : Nat} {x : BitVec w} :
 
 @[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]
+  simp [zeroExtend']
 
 @[bv_toNat] theorem toNat_zeroExtend (i : Nat) (x : BitVec n) :
     BitVec.toNat (zeroExtend i x) = x.toNat % 2^i := by
@@ -436,6 +447,12 @@ theorem zeroExtend_ofNat_one_eq_ofNat_one_of_lt {v w : Nat} (hv : 0 < v) :
   have hv := Nat.testBit_one_eq_true_iff_self_eq_zero.mp hi₁
   omega
 
+/-- Truncating to width 1 produces a bitvector equal to the least significant bit. -/
+theorem truncate_one {x : BitVec w} :
+    x.truncate 1 = ofBool (x.getLsb 0) := by
+  ext i
+  simp [show i = 0 by omega]
+
 /-! ## extractLsb -/
 
 @[simp]
@@ -455,10 +472,18 @@ protected theorem extractLsb_ofNat (x n : Nat) (hi lo : Nat) :
 @[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_extractLsb' (start len : Nat) (x : BitVec n) (i : Nat) :
+    (extractLsb' start len x).getLsb i = (i < len && x.getLsb (start+i)) := by
+  simp [getLsb, Nat.lt_succ]
+
 @[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]
+  simp [getLsb, Nat.lt_succ]
+
+theorem extractLsb'_eq_extractLsb {w : Nat} (x : BitVec w) (start len : Nat) (h : len > 0) :
+    x.extractLsb' start len = (x.extractLsb (len - 1 + start) start).cast (by omega) := by
+  apply eq_of_toNat_eq
+  simp [extractLsb, show len - 1 + 1 = len by omega]
 
 /-! ### allOnes -/
 
@@ -499,6 +524,13 @@ theorem or_assoc (x y z : BitVec w) :
     x ||| y ||| z = x ||| (y ||| z) := by
   ext i
   simp [Bool.or_assoc]
+instance : Std.Associative (α := BitVec n) (· ||| ·) := ⟨BitVec.or_assoc⟩
+
+theorem or_comm (x y : BitVec w) :
+    x ||| y = y ||| x := by
+  ext i
+  simp [Bool.or_comm]
+instance : Std.Commutative (fun (x y : BitVec w) => x ||| y) := ⟨BitVec.or_comm⟩
 
 /-! ### and -/
 
@@ -530,6 +562,13 @@ theorem and_assoc (x y z : BitVec w) :
     x &&& y &&& z = x &&& (y &&& z) := by
   ext i
   simp [Bool.and_assoc]
+instance : Std.Associative (α := BitVec n) (· &&& ·) := ⟨BitVec.and_assoc⟩
+
+theorem and_comm (x y : BitVec w) :
+    x &&& y = y &&& x := by
+  ext i
+  simp [Bool.and_comm]
+instance : Std.Commutative (fun (x y : BitVec w) => x &&& y) := ⟨BitVec.and_comm⟩
 
 /-! ### xor -/
 
@@ -546,6 +585,15 @@ theorem and_assoc (x y z : BitVec w) :
   rw [← testBit_toNat, getLsb, getLsb]
   simp
 
+@[simp] theorem getMsb_xor {x y : BitVec w} :
+    (x ^^^ y).getMsb i = (xor (x.getMsb i) (y.getMsb i)) := by
+  simp only [getMsb]
+  by_cases h : i < w <;> simp [h]
+
+@[simp] theorem msb_xor {x y : BitVec w} :
+    (x ^^^ y).msb = (xor x.msb y.msb) := by
+  simp [BitVec.msb]
+
 @[simp] theorem truncate_xor {x y : BitVec w} :
     (x ^^^ y).truncate k = x.truncate k ^^^ y.truncate k := by
   ext
@@ -555,6 +603,13 @@ theorem xor_assoc (x y z : BitVec w) :
     x ^^^ y ^^^ z = x ^^^ (y ^^^ z) := by
   ext i
   simp [Bool.xor_assoc]
+instance : Std.Associative (fun (x y : BitVec w) => x ^^^ y) := ⟨BitVec.xor_assoc⟩
+
+theorem xor_comm (x y : BitVec w) :
+    x ^^^ y = y ^^^ x := by
+  ext i
+  simp [Bool.xor_comm]
+instance : Std.Commutative (fun (x y : BitVec w) => x ^^^ y) := ⟨BitVec.xor_comm⟩
 
 /-! ### not -/
 
@@ -626,6 +681,10 @@ theorem shiftLeft_zero_eq (x : BitVec w) : x <<< 0 = x := by
   apply eq_of_toNat_eq
   simp
 
+@[simp]
+theorem zero_shiftLeft (n : Nat) : 0#w <<< n = 0#w := by
+  simp [bv_toNat]
+
 @[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]
@@ -634,6 +693,27 @@ theorem shiftLeft_zero_eq (x : BitVec w) : x <<< 0 = x := by
   cases h₁ : decide (i < m) <;> cases h₂ : decide (n ≤ i) <;> cases h₃ : decide (i < n)
   all_goals { simp_all <;> omega }
 
+theorem shiftLeft_xor_distrib (x y : BitVec w) (n : Nat) :
+    (x ^^^ y) <<< n = (x <<< n) ^^^ (y <<< n) := by
+  ext i
+  simp only [getLsb_shiftLeft, Fin.is_lt, decide_True, Bool.true_and, getLsb_xor]
+  by_cases h : i < n
+    <;> simp [h]
+
+theorem shiftLeft_and_distrib (x y : BitVec w) (n : Nat) :
+    (x &&& y) <<< n = (x <<< n) &&& (y <<< n) := by
+  ext i
+  simp only [getLsb_shiftLeft, Fin.is_lt, decide_True, Bool.true_and, getLsb_and]
+  by_cases h : i < n
+    <;> simp [h]
+
+theorem shiftLeft_or_distrib (x y : BitVec w) (n : Nat) :
+    (x ||| y) <<< n = (x <<< n) ||| (y <<< n) := by
+  ext i
+  simp only [getLsb_shiftLeft, Fin.is_lt, decide_True, Bool.true_and, getLsb_or]
+  by_cases h : i < n
+    <;> simp [h]
+
 @[simp] theorem getMsb_shiftLeft (x : BitVec w) (i) :
     (x <<< i).getMsb k = x.getMsb (k + i) := by
   simp only [getMsb, getLsb_shiftLeft]
@@ -691,6 +771,22 @@ theorem shiftLeft_shiftLeft {w : Nat} (x : BitVec w) (n m : Nat) :
     (x <<< n) <<< m = x <<< (n + m) := by
   rw [shiftLeft_add]
 
+/-! ### shiftLeft reductions from BitVec to Nat -/
+
+@[simp]
+theorem shiftLeft_eq' {x : BitVec w₁} {y : BitVec w₂} : x <<< y = x <<< y.toNat := by rfl
+
+@[simp]
+theorem shiftLeft_zero' {x : BitVec w₁} : x <<< 0#w₂ = x := by simp
+
+theorem shiftLeft_shiftLeft' {x : BitVec w₁} {y : BitVec w₂} {z : BitVec w₃} :
+    x <<< y <<< z = x <<< (y.toNat + z.toNat) := by
+  simp [shiftLeft_add]
+
+theorem getLsb_shiftLeft' {x : BitVec w₁} {y : BitVec w₂} {i : Nat} :
+    (x <<< y).getLsb i = (decide (i < w₁) && !decide (i < y.toNat) && x.getLsb (i - y.toNat)) := by
+  simp [shiftLeft_eq', getLsb_shiftLeft]
+
 /-! ### ushiftRight -/
 
 @[simp, bv_toNat] theorem toNat_ushiftRight (x : BitVec n) (i : Nat) :
@@ -700,6 +796,31 @@ theorem shiftLeft_shiftLeft {w : Nat} (x : BitVec w) (n m : Nat) :
     getLsb (x >>> i) j = getLsb x (i+j) := by
   unfold getLsb ; simp
 
+theorem ushiftRight_xor_distrib (x y : BitVec w) (n : Nat) :
+    (x ^^^ y) >>> n = (x >>> n) ^^^ (y >>> n) := by
+  ext
+  simp
+
+theorem ushiftRight_and_distrib (x y : BitVec w) (n : Nat) :
+    (x &&& y) >>> n = (x >>> n) &&& (y >>> n) := by
+  ext
+  simp
+
+theorem ushiftRight_or_distrib (x y : BitVec w)  (n : Nat) :
+    (x ||| y) >>> n = (x >>> n) ||| (y >>> n) := by
+  ext
+  simp
+
+@[simp]
+theorem ushiftRight_zero_eq (x : BitVec w) : x >>> 0 = x := by
+  simp [bv_toNat]
+
+/-! ### ushiftRight reductions from BitVec to Nat -/
+
+@[simp]
+theorem ushiftRight_eq' (x : BitVec w₁) (y : BitVec w₂) :
+    x >>> y = x >>> y.toNat := by rfl
+
 /-! ### sshiftRight -/
 
 theorem sshiftRight_eq {x : BitVec n} {i : Nat} :
@@ -743,7 +864,7 @@ theorem sshiftRight_eq_of_msb_true {x : BitVec w} {s : Nat} (h : x.msb = true) :
     · rw [Nat.shiftRight_eq_div_pow]
       apply Nat.lt_of_le_of_lt (Nat.div_le_self _ _) (by omega)
 
-theorem getLsb_sshiftRight (x : BitVec w) (s i : Nat) :
+@[simp] theorem getLsb_sshiftRight (x : BitVec w) (s i : Nat) :
     getLsb (x.sshiftRight s) i =
       (!decide (w ≤ i) && if s + i < w then x.getLsb (s + i) else x.msb) := by
   rcases hmsb : x.msb with rfl | rfl
@@ -764,6 +885,90 @@ theorem getLsb_sshiftRight (x : BitVec w) (s i : Nat) :
         Nat.not_lt, decide_eq_true_eq]
       omega
 
+theorem sshiftRight_xor_distrib (x y : BitVec w) (n : Nat) :
+    (x ^^^ y).sshiftRight n = (x.sshiftRight n) ^^^ (y.sshiftRight n) := by
+  ext i
+  simp only [getLsb_sshiftRight, getLsb_xor, msb_xor]
+  split
+    <;> by_cases w ≤ i
+    <;> simp [*]
+
+theorem sshiftRight_and_distrib (x y : BitVec w) (n : Nat) :
+    (x &&& y).sshiftRight n = (x.sshiftRight n) &&& (y.sshiftRight n) := by
+  ext i
+  simp only [getLsb_sshiftRight, getLsb_and, msb_and]
+  split
+    <;> by_cases w ≤ i
+    <;> simp [*]
+
+theorem sshiftRight_or_distrib (x y : BitVec w) (n : Nat) :
+    (x ||| y).sshiftRight n = (x.sshiftRight n) ||| (y.sshiftRight n) := by
+  ext i
+  simp only [getLsb_sshiftRight, getLsb_or, msb_or]
+  split
+    <;> by_cases w ≤ i
+    <;> simp [*]
+
+/-- The msb after arithmetic shifting right equals the original msb. -/
+theorem sshiftRight_msb_eq_msb {n : Nat} {x : BitVec w} :
+    (x.sshiftRight n).msb = x.msb := by
+  rw [msb_eq_getLsb_last, getLsb_sshiftRight, msb_eq_getLsb_last]
+  by_cases hw₀ : w = 0
+  · simp [hw₀]
+  · simp only [show ¬(w ≤ w - 1) by omega, decide_False, Bool.not_false, Bool.true_and,
+      ite_eq_right_iff]
+    intros h
+    simp [show n = 0 by omega]
+
+@[simp] theorem sshiftRight_zero {x : BitVec w} : x.sshiftRight 0 = x := by
+  ext i
+  simp
+
+theorem sshiftRight_add {x : BitVec w} {m n : Nat} :
+    x.sshiftRight (m + n) = (x.sshiftRight m).sshiftRight n := by
+  ext i
+  simp only [getLsb_sshiftRight, Nat.add_assoc]
+  by_cases h₁ : w ≤ (i : Nat)
+  · simp [h₁]
+  · simp only [h₁, decide_False, Bool.not_false, Bool.true_and]
+    by_cases h₂ : n + ↑i < w
+    · simp [h₂]
+    · simp only [h₂, ↓reduceIte]
+      by_cases h₃ : m + (n + ↑i) < w
+      · simp [h₃]
+        omega
+      · simp [h₃, sshiftRight_msb_eq_msb]
+
+/-! ### sshiftRight reductions from BitVec to Nat -/
+
+@[simp]
+theorem sshiftRight_eq' (x : BitVec w) : x.sshiftRight' y = x.sshiftRight y.toNat := rfl
+
+/-! ### udiv -/
+
+theorem udiv_eq {x y : BitVec n} : x.udiv y = BitVec.ofNat n (x.toNat / y.toNat) := by
+  have h : x.toNat / y.toNat < 2 ^ n := Nat.lt_of_le_of_lt (Nat.div_le_self ..) (by omega)
+  simp [udiv, bv_toNat, h, Nat.mod_eq_of_lt]
+
+@[simp, bv_toNat]
+theorem toNat_udiv {x y : BitVec n} : (x.udiv y).toNat = x.toNat / y.toNat := by
+  simp only [udiv_eq]
+  by_cases h : y = 0
+  · simp [h]
+  · rw [toNat_ofNat, Nat.mod_eq_of_lt]
+    exact Nat.lt_of_le_of_lt (Nat.div_le_self ..) (by omega)
+
+/-! ### umod -/
+
+theorem umod_eq {x y : BitVec n} :
+    x.umod y = BitVec.ofNat n (x.toNat % y.toNat) := by
+  have h : x.toNat % y.toNat < 2 ^ n := Nat.lt_of_le_of_lt (Nat.mod_le _ _) x.isLt
+  simp [umod, bv_toNat, Nat.mod_eq_of_lt h]
+
+@[simp, bv_toNat]
+theorem toNat_umod {x y : BitVec n} :
+    (x.umod y).toNat = x.toNat % y.toNat := rfl
+
 /-! ### signExtend -/
 
 /-- Equation theorem for `Int.sub` when both arguments are `Int.ofNat` -/
@@ -826,15 +1031,15 @@ theorem append_def (x : BitVec v) (y : BitVec w) :
     (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] theorem getLsb_append {x : BitVec n} {y : BitVec m} :
+    getLsb (x ++ y) i = bif i < m then getLsb y i else getLsb x (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] theorem getMsb_append {x : BitVec n} {y : BitVec m} :
+    getMsb (x ++ y) i = bif n ≤ i then getMsb y (i - n) else getMsb x i := by
   simp [append_def]
   by_cases h : n ≤ i
   · simp [h]
@@ -1155,6 +1360,19 @@ theorem neg_eq_not_add (x : BitVec w) : -x = ~~~x + 1 := by
   have hx : x.toNat < 2^w := x.isLt
   rw [Nat.sub_sub, Nat.add_comm 1 x.toNat, ← Nat.sub_sub, Nat.sub_add_cancel (by omega)]
 
+@[simp]
+theorem neg_neg {x : BitVec w} : - - x = x := by
+  by_cases h : x = 0#w
+  · simp [h]
+  · simp [bv_toNat, h]
+
+theorem neg_ne_iff_ne_neg {x y : BitVec w} : -x ≠ y ↔ x ≠ -y := by
+  constructor
+  all_goals
+    intro h h'
+    subst h'
+    simp at h
+
 /-! ### mul -/
 
 theorem mul_def {n} {x y : BitVec n} : x * y = (ofFin <| x.toFin * y.toFin) := by rfl
@@ -1452,12 +1670,18 @@ theorem getLsb_twoPow (i j : Nat) : (twoPow w i).getLsb j = ((i < w) && (i = j))
           simp at hi
         simp_all
 
-theorem and_twoPow_eq (x : BitVec w) (i : Nat) :
+@[simp]
+theorem and_twoPow (x : BitVec w) (i : Nat) :
     x &&& (twoPow w i) = if x.getLsb i then twoPow w i else 0#w := by
   ext j
   simp only [getLsb_and, getLsb_twoPow]
   by_cases hj : i = j <;> by_cases hx : x.getLsb i <;> simp_all
 
+@[simp]
+theorem twoPow_and (x : BitVec w) (i : Nat) :
+    (twoPow w i) &&& x = if x.getLsb i then twoPow w i else 0#w := by
+  rw [BitVec.and_comm, and_twoPow]
+
 @[simp]
 theorem mul_twoPow_eq_shiftLeft (x : BitVec w) (i : Nat) :
     x * (twoPow w i) = x <<< i := by
@@ -1471,6 +1695,14 @@ theorem mul_twoPow_eq_shiftLeft (x : BitVec w) (i : Nat) :
       apply Nat.pow_dvd_pow 2 (by omega)
     simp [Nat.mul_mod, hpow]
 
+theorem twoPow_zero {w : Nat} : twoPow w 0 = 1#w := by
+  apply eq_of_toNat_eq
+  simp
+
+@[simp]
+theorem getLsb_one {w i : Nat} : (1#w).getLsb i = (decide (0 < w) && decide (0 = i)) := by
+  rw [← twoPow_zero, getLsb_twoPow]
+
 /- ### zeroExtend, truncate, and bitwise operations -/
 
 /--
@@ -1504,4 +1736,54 @@ theorem zeroExtend_truncate_succ_eq_zeroExtend_truncate_or_twoPow_of_getLsb_true
     simp [hx]
   · by_cases hik' : k < i + 1 <;> simp [hik, hik'] <;> omega
 
+/-- Bitwise and of `(x : BitVec w)` with `1#w` equals zero extending `x.lsb` to `w`. -/
+theorem and_one_eq_zeroExtend_ofBool_getLsb {x : BitVec w} :
+    (x &&& 1#w) = zeroExtend w (ofBool (x.getLsb 0)) := by
+  ext i
+  simp only [getLsb_and, getLsb_one, getLsb_zeroExtend, Fin.is_lt, decide_True, getLsb_ofBool,
+    Bool.true_and]
+  by_cases h : (0 = (i : Nat)) <;> simp [h] <;> omega
+
+@[simp]
+theorem replicate_zero_eq {x : BitVec w} : x.replicate 0 = 0#0 := by
+  simp [replicate]
+
+@[simp]
+theorem replicate_succ_eq {x : BitVec w} :
+    x.replicate (n + 1) =
+    (x ++ replicate n x).cast (by rw [Nat.mul_succ]; omega) := by
+  simp [replicate]
+
+/--
+If a number `w * n ≤ i < w * (n + 1)`, then `i - w * n` equals `i % w`.
+This is true by subtracting `w * n` from the inequality, giving
+`0 ≤ i - w * n < w`, which uniquely identifies `i % w`.
+-/
+private theorem Nat.sub_mul_eq_mod_of_lt_of_le (hlo : w * n ≤ i) (hhi : i < w * (n + 1)) :
+    i - w * n = i % w := by
+  rw [Nat.mod_def]
+  congr
+  symm
+  apply Nat.div_eq_of_lt_le
+    (by rw [Nat.mul_comm]; omega)
+    (by rw [Nat.mul_comm]; omega)
+
+@[simp]
+theorem getLsb_replicate {n w : Nat} (x : BitVec w) :
+    (x.replicate n).getLsb i =
+    (decide (i < w * n) && x.getLsb (i % w)) := by
+  induction n generalizing x
+  case zero => simp
+  case succ n ih =>
+    simp only [replicate_succ_eq, getLsb_cast, getLsb_append]
+    by_cases hi : i < w * (n + 1)
+    · simp only [hi, decide_True, Bool.true_and]
+      by_cases hi' : i < w * n
+      · simp [hi', ih]
+      · simp only [hi', decide_False, cond_false]
+        rw [Nat.sub_mul_eq_mod_of_lt_of_le] <;> omega
+    · rw [Nat.mul_succ] at hi ⊢
+      simp only [show ¬i < w * n by omega, decide_False, cond_false, hi, Bool.false_and]
+      apply BitVec.getLsb_ge (x := x) (i := i - w * n) (ge := by omega)
+
 end BitVec

src/Init/Data/Bool.lean

@@ -438,6 +438,24 @@ Added for confluence between `if_true_left` and `ite_false_same` on
 -/
 @[simp] theorem eq_true_imp_eq_false : ∀(b:Bool), (b = true → b = false) ↔ (b = false) := by decide
 
+/-! ### forall -/
+
+theorem forall_bool' {p : Bool → Prop} (b : Bool) : (∀ x, p x) ↔ p b ∧ p !b :=
+  ⟨fun h ↦ ⟨h _, h _⟩, fun ⟨h₁, h₂⟩ x ↦ by cases b <;> cases x <;> assumption⟩
+
+@[simp]
+theorem forall_bool {p : Bool → Prop} : (∀ b, p b) ↔ p false ∧ p true :=
+  forall_bool' false
+
+/-! ### exists -/
+
+theorem exists_bool' {p : Bool → Prop} (b : Bool) : (∃ x, p x) ↔ p b ∨ p !b :=
+  ⟨fun ⟨x, hx⟩ ↦ by cases x <;> cases b <;> first | exact .inl ‹_› | exact .inr ‹_›,
+    fun h ↦ by cases h <;> exact ⟨_, ‹_›⟩⟩
+
+@[simp]
+theorem exists_bool {p : Bool → Prop} : (∃ b, p b) ↔ p false ∨ p true :=
+  exists_bool' false
 
 /-! ### cond -/
 
@@ -531,3 +549,19 @@ export Bool (cond_eq_if)
 
 @[simp] theorem true_eq_decide_iff {p : Prop} [h : Decidable p] : true = decide p ↔ p := by
   cases h with | _ q => simp [q]
+
+/-! ### coercions -/
+
+/--
+This should not be turned on globally as an instance because it degrades performance in Mathlib,
+but may be used locally.
+-/
+def boolPredToPred : Coe (α → Bool) (α  → Prop) where
+  coe r := fun a => Eq (r a) true
+
+/--
+This should not be turned on globally as an instance because it degrades performance in Mathlib,
+but may be used locally.
+-/
+def boolRelToRel : Coe (α → α → Bool) (α → α → Prop) where
+  coe r := fun a b => Eq (r a b) true

src/Init/Data/ByteArray/Basic.lean

@@ -37,6 +37,10 @@ def push : ByteArray → UInt8 → ByteArray
 def size : (@& ByteArray) → Nat
   | ⟨bs⟩ => bs.size
 
+@[extern "lean_sarray_size", simp]
+def usize (a : @& ByteArray) : USize :=
+  a.size.toUSize
+
 @[extern "lean_byte_array_uget"]
 def uget : (a : @& ByteArray) → (i : USize) → i.toNat < a.size → UInt8
   | ⟨bs⟩, i, h => bs[i]
@@ -119,7 +123,7 @@ def toList (bs : ByteArray) : List UInt8 :=
   TODO: avoid code duplication in the future after we improve the compiler.
 -/
 @[inline] unsafe def forInUnsafe {β : Type v} {m : Type v → Type w} [Monad m] (as : ByteArray) (b : β) (f : UInt8 → β → m (ForInStep β)) : m β :=
-  let sz := USize.ofNat as.size
+  let sz := as.usize
   let rec @[specialize] loop (i : USize) (b : β) : m β := do
     if i < sz then
       let a := as.uget i lcProof
@@ -187,6 +191,121 @@ def foldlM {β : Type v} {m : Type v → Type w} [Monad m] (f : β → UInt8 →
 def foldl {β : Type v} (f : β → UInt8 → β) (init : β) (as : ByteArray) (start := 0) (stop := as.size) : β :=
   Id.run <| as.foldlM f init start stop
 
+/-- Iterator over the bytes (`UInt8`) of a `ByteArray`.
+
+Typically created by `arr.iter`, where `arr` is a `ByteArray`.
+
+An iterator is *valid* if the position `i` is *valid* for the array `arr`, meaning `0 ≤ i ≤ arr.size`
+
+Most operations on iterators return arbitrary values if the iterator is not valid. The functions in
+the `ByteArray.Iterator` API should rule out the creation of invalid iterators, with two exceptions:
+
+- `Iterator.next iter` is invalid if `iter` is already at the end of the array (`iter.atEnd` is
+  `true`)
+- `Iterator.forward iter n`/`Iterator.nextn iter n` is invalid if `n` is strictly greater than the
+  number of remaining bytes.
+-/
+structure Iterator where
+  /-- The array the iterator is for. -/
+  array : ByteArray
+  /-- The current position.
+
+  This position is not necessarily valid for the array, for instance if one keeps calling
+  `Iterator.next` when `Iterator.atEnd` is true. If the position is not valid, then the
+  current byte is `(default : UInt8)`. -/
+  idx : Nat
+  deriving Inhabited
+
+/-- Creates an iterator at the beginning of an array. -/
+def mkIterator (arr : ByteArray) : Iterator :=
+  ⟨arr, 0⟩
+
+@[inherit_doc mkIterator]
+abbrev iter := mkIterator
+
+/-- The size of an array iterator is the number of bytes remaining. -/
+instance : SizeOf Iterator where
+  sizeOf i := i.array.size - i.idx
+
+theorem Iterator.sizeOf_eq (i : Iterator) : sizeOf i = i.array.size - i.idx :=
+  rfl
+
+namespace Iterator
+
+/-- Number of bytes remaining in the iterator. -/
+def remainingBytes : Iterator → Nat
+  | ⟨arr, i⟩ => arr.size - i
+
+@[inherit_doc Iterator.idx]
+def pos := Iterator.idx
+
+/-- The byte at the current position.
+
+On an invalid position, returns `(default : UInt8)`. -/
+@[inline]
+def curr : Iterator → UInt8
+  | ⟨arr, i⟩ =>
+    if h:i < arr.size then
+      arr[i]'h
+    else
+      default
+
+/-- Moves the iterator's position forward by one byte, unconditionally.
+
+It is only valid to call this function if the iterator is not at the end of the array, *i.e.*
+`Iterator.atEnd` is `false`; otherwise, the resulting iterator will be invalid. -/
+@[inline]
+def next : Iterator → Iterator
+  | ⟨arr, i⟩ => ⟨arr, i + 1⟩
+
+/-- Decreases the iterator's position.
+
+If the position is zero, this function is the identity. -/
+@[inline]
+def prev : Iterator → Iterator
+  | ⟨arr, i⟩ => ⟨arr, i - 1⟩
+
+/-- True if the iterator is past the array's last byte. -/
+@[inline]
+def atEnd : Iterator → Bool
+  | ⟨arr, i⟩ => i ≥ arr.size
+
+/-- True if the iterator is not past the array's last byte. -/
+@[inline]
+def hasNext : Iterator → Bool
+  | ⟨arr, i⟩ => i < arr.size
+
+/-- True if the position is not zero. -/
+@[inline]
+def hasPrev : Iterator → Bool
+  | ⟨_, i⟩ => i > 0
+
+/-- Moves the iterator's position to the end of the array.
+
+Note that `i.toEnd.atEnd` is always `true`. -/
+@[inline]
+def toEnd : Iterator → Iterator
+  | ⟨arr, _⟩ => ⟨arr, arr.size⟩
+
+/-- Moves the iterator's position several bytes forward.
+
+The resulting iterator is only valid if the number of bytes to skip is less than or equal to
+the number of bytes left in the iterator. -/
+@[inline]
+def forward : Iterator → Nat → Iterator
+  | ⟨arr, i⟩, f => ⟨arr, i + f⟩
+
+@[inherit_doc forward, inline]
+def nextn : Iterator → Nat → Iterator := forward
+
+/-- Moves the iterator's position several bytes back.
+
+If asked to go back more bytes than available, stops at the beginning of the array. -/
+@[inline]
+def prevn : Iterator → Nat → Iterator
+  | ⟨arr, i⟩, f => ⟨arr, i - f⟩
+
+end Iterator
 end ByteArray
 
 def List.toByteArray (bs : List UInt8) : ByteArray :=

src/Init/Data/Fin/Basic.lean

@@ -149,6 +149,9 @@ instance : Inhabited (Fin (no_index (n+1))) where
 
 @[simp] theorem zero_eta : (⟨0, Nat.zero_lt_succ _⟩ : Fin (n + 1)) = 0 := rfl
 
+theorem ne_of_val_ne {i j : Fin n} (h : val i ≠ val j) : i ≠ j :=
+  fun h' => absurd (val_eq_of_eq h') h
+
 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
 

src/Init/Data/FloatArray/Basic.lean

@@ -37,6 +37,10 @@ def push : FloatArray → Float → FloatArray
 def size : (@& FloatArray) → Nat
   | ⟨ds⟩ => ds.size
 
+@[extern "lean_sarray_size", simp]
+def usize (a : @& FloatArray) : USize :=
+  a.size.toUSize
+
 @[extern "lean_float_array_uget"]
 def uget : (a : @& FloatArray) → (i : USize) → i.toNat < a.size → Float
   | ⟨ds⟩, i, h => ds[i]
@@ -90,7 +94,7 @@ partial def toList (ds : FloatArray) : List Float :=
 -/
 -- TODO: avoid code duplication in the future after we improve the compiler.
 @[inline] unsafe def forInUnsafe {β : Type v} {m : Type v → Type w} [Monad m] (as : FloatArray) (b : β) (f : Float → β → m (ForInStep β)) : m β :=
-  let sz := USize.ofNat as.size
+  let sz := as.usize
   let rec @[specialize] loop (i : USize) (b : β) : m β := do
     if i < sz then
       let a := as.uget i lcProof

src/Init/Data/Int/Basic.lean

@@ -322,8 +322,8 @@ protected def pow (m : Int) : Nat → Int
   | 0      => 1
   | succ n => Int.pow m n * m
 
-instance : HPow Int Nat Int where
-  hPow := Int.pow
+instance : NatPow Int where
+  pow := Int.pow
 
 instance : LawfulBEq Int where
   eq_of_beq h := by simp [BEq.beq] at h; assumption

src/Init/Data/List.lean

@@ -4,11 +4,22 @@ Released under Apache 2.0 license as described in the file LICENSE.
 Authors: Leonardo de Moura
 -/
 prelude
+import Init.Data.List.Attach
 import Init.Data.List.Basic
 import Init.Data.List.BasicAux
 import Init.Data.List.Control
-import Init.Data.List.Lemmas
-import Init.Data.List.Attach
+import Init.Data.List.Count
+import Init.Data.List.Erase
+import Init.Data.List.Find
 import Init.Data.List.Impl
-import Init.Data.List.TakeDrop
+import Init.Data.List.Lemmas
+import Init.Data.List.MinMax
+import Init.Data.List.Monadic
+import Init.Data.List.Nat
 import Init.Data.List.Notation
+import Init.Data.List.Pairwise
+import Init.Data.List.Sublist
+import Init.Data.List.TakeDrop
+import Init.Data.List.Zip
+import Init.Data.List.Perm
+import Init.Data.List.Sort

src/Init/Data/List/Attach.lean

@@ -4,7 +4,8 @@ Released under Apache 2.0 license as described in the file LICENSE.
 Authors: Mario Carneiro
 -/
 prelude
-import Init.Data.List.Lemmas
+import Init.Data.List.Count
+import Init.Data.Subtype
 
 namespace List
 
@@ -44,3 +45,155 @@ Unsafe implementation of `attachWith`, taking advantage of the fact that the rep
   | nil, hL' => rfl
   | cons _ L', hL' => congrArg _ <| go L' fun _ hx => hL' (.tail _ hx)
   exact go L h'
+
+@[simp] theorem attach_nil : ([] : List α).attach = [] := rfl
+
+@[simp]
+theorem pmap_eq_map (p : α → Prop) (f : α → β) (l : List α) (H) :
+    @pmap _ _ p (fun a _ => f a) l H = map f l := by
+  induction l
+  · rfl
+  · simp only [*, pmap, map]
+
+theorem pmap_congr {p q : α → Prop} {f : ∀ a, p a → β} {g : ∀ a, q a → β} (l : List α) {H₁ H₂}
+    (h : ∀ a ∈ l, ∀ (h₁ h₂), f a h₁ = g a h₂) : pmap f l H₁ = pmap g l H₂ := by
+  induction l with
+  | nil => rfl
+  | cons x l ih => rw [pmap, pmap, h _ (mem_cons_self _ _), ih fun a ha => h a (mem_cons_of_mem _ ha)]
+
+theorem map_pmap {p : α → Prop} (g : β → γ) (f : ∀ a, p a → β) (l H) :
+    map g (pmap f l H) = pmap (fun a h => g (f a h)) l H := by
+  induction l
+  · rfl
+  · simp only [*, pmap, map]
+
+theorem pmap_map {p : β → Prop} (g : ∀ b, p b → γ) (f : α → β) (l H) :
+    pmap g (map f l) H = pmap (fun a h => g (f a) h) l fun a h => H _ (mem_map_of_mem _ h) := by
+  induction l
+  · rfl
+  · simp only [*, pmap, map]
+
+theorem pmap_eq_map_attach {p : α → Prop} (f : ∀ a, p a → β) (l H) :
+    pmap f l H = l.attach.map fun x => f x.1 (H _ x.2) := by
+  rw [attach, attachWith, map_pmap]; exact pmap_congr l fun _ _ _ _ => rfl
+
+theorem attach_map_coe (l : List α) (f : α → β) :
+    (l.attach.map fun (i : {i // i ∈ l}) => f i) = l.map f := by
+  rw [attach, attachWith, map_pmap]; exact pmap_eq_map _ _ _ _
+
+theorem attach_map_val (l : List α) (f : α → β) : (l.attach.map fun i => f i.val) = l.map f :=
+  attach_map_coe _ _
+
+@[simp]
+theorem attach_map_subtype_val (l : List α) : l.attach.map Subtype.val = l :=
+  (attach_map_coe _ _).trans l.map_id
+
+theorem countP_attach (l : List α) (p : α → Bool) : l.attach.countP (fun a : {x // x ∈ l} => p a) = l.countP p := by
+  simp only [← Function.comp_apply (g := Subtype.val), ← countP_map, attach_map_subtype_val]
+
+@[simp]
+theorem count_attach [DecidableEq α] (l : List α) (a : {x // x ∈ l}) : l.attach.count a = l.count ↑a :=
+  Eq.trans (countP_congr fun _ _ => by simp [Subtype.ext_iff]) <| countP_attach _ _
+
+@[simp]
+theorem mem_attach (l : List α) : ∀ x, x ∈ l.attach
+  | ⟨a, h⟩ => by
+    have := mem_map.1 (by rw [attach_map_subtype_val] <;> exact h)
+    rcases this with ⟨⟨_, _⟩, m, rfl⟩
+    exact m
+
+@[simp]
+theorem mem_pmap {p : α → Prop} {f : ∀ a, p a → β} {l H b} :
+    b ∈ pmap f l H ↔ ∃ (a : _) (h : a ∈ l), f a (H a h) = b := by
+  simp only [pmap_eq_map_attach, mem_map, mem_attach, true_and, Subtype.exists, eq_comm]
+
+@[simp]
+theorem length_pmap {p : α → Prop} {f : ∀ a, p a → β} {l H} : length (pmap f l H) = length l := by
+  induction l
+  · rfl
+  · simp only [*, pmap, length]
+
+@[simp]
+theorem length_attach (L : List α) : L.attach.length = L.length :=
+  length_pmap
+
+@[simp]
+theorem pmap_eq_nil {p : α → Prop} {f : ∀ a, p a → β} {l H} : pmap f l H = [] ↔ l = [] := by
+  rw [← length_eq_zero, length_pmap, length_eq_zero]
+
+@[simp]
+theorem attach_eq_nil (l : List α) : l.attach = [] ↔ l = [] :=
+  pmap_eq_nil
+
+theorem getLast_pmap (p : α → Prop) (f : ∀ a, p a → β) (l : List α)
+    (hl₁ : ∀ a ∈ l, p a) (hl₂ : l ≠ []) :
+    (l.pmap f hl₁).getLast (mt List.pmap_eq_nil.1 hl₂) =
+      f (l.getLast hl₂) (hl₁ _ (List.getLast_mem hl₂)) := by
+  induction l with
+  | nil => apply (hl₂ rfl).elim
+  | cons l_hd l_tl l_ih =>
+    by_cases hl_tl : l_tl = []
+    · simp [hl_tl]
+    · simp only [pmap]
+      rw [getLast_cons, l_ih _ hl_tl]
+      simp only [getLast_cons hl_tl]
+
+theorem getElem?_pmap {p : α → Prop} (f : ∀ a, p a → β) {l : List α} (h : ∀ a ∈ l, p a) (n : Nat) :
+    (pmap f l h)[n]? = Option.pmap f l[n]? fun x H => h x (getElem?_mem H) := by
+  induction l generalizing n with
+  | nil => simp
+  | cons hd tl hl =>
+    rcases n with ⟨n⟩
+    · simp only [Option.pmap]
+      split <;> simp_all
+    · simp only [hl, pmap, Option.pmap, getElem?_cons_succ]
+      split <;> rename_i h₁ _ <;> split <;> rename_i h₂ _
+      · simp_all
+      · simp at h₂
+        simp_all
+      · simp_all
+      · simp_all
+
+theorem get?_pmap {p : α → Prop} (f : ∀ a, p a → β) {l : List α} (h : ∀ a ∈ l, p a) (n : Nat) :
+    get? (pmap f l h) n = Option.pmap f (get? l n) fun x H => h x (get?_mem H) := by
+  simp only [get?_eq_getElem?]
+  simp [getElem?_pmap, h]
+
+theorem getElem_pmap {p : α → Prop} (f : ∀ a, p a → β) {l : List α} (h : ∀ a ∈ l, p a) {n : Nat}
+    (hn : n < (pmap f l h).length) :
+    (pmap f l h)[n] =
+      f (l[n]'(@length_pmap _ _ p f l h ▸ hn))
+        (h _ (getElem_mem l n (@length_pmap _ _ p f l h ▸ hn))) := by
+  induction l generalizing n with
+  | nil =>
+    simp only [length, pmap] at hn
+    exact absurd hn (Nat.not_lt_of_le n.zero_le)
+  | cons hd tl hl =>
+    cases n
+    · simp
+    · simp [hl]
+
+theorem get_pmap {p : α → Prop} (f : ∀ a, p a → β) {l : List α} (h : ∀ a ∈ l, p a) {n : Nat}
+    (hn : n < (pmap f l h).length) :
+    get (pmap f l h) ⟨n, hn⟩ =
+      f (get l ⟨n, @length_pmap _ _ p f l h ▸ hn⟩)
+        (h _ (get_mem l n (@length_pmap _ _ p f l h ▸ hn))) := by
+  simp only [get_eq_getElem]
+  simp [getElem_pmap]
+
+theorem pmap_append {p : ι → Prop} (f : ∀ a : ι, p a → α) (l₁ l₂ : List ι)
+    (h : ∀ a ∈ l₁ ++ l₂, p a) :
+    (l₁ ++ l₂).pmap f h =
+      (l₁.pmap f fun a ha => h a (mem_append_left l₂ ha)) ++
+        l₂.pmap f fun a ha => h a (mem_append_right l₁ ha) := by
+  induction l₁ with
+  | nil => rfl
+  | cons _ _ ih =>
+    dsimp only [pmap, cons_append]
+    rw [ih]
+
+theorem pmap_append' {p : α → Prop} (f : ∀ a : α, p a → β) (l₁ l₂ : List α)
+    (h₁ : ∀ a ∈ l₁, p a) (h₂ : ∀ a ∈ l₂, p a) :
+    ((l₁ ++ l₂).pmap f fun a ha => (List.mem_append.1 ha).elim (h₁ a) (h₂ a)) =
+      l₁.pmap f h₁ ++ l₂.pmap f h₂ :=
+  pmap_append f l₁ l₂ _

src/Init/Data/List/Basic.lean

@@ -27,24 +27,32 @@ Recall that `length`, `get`, `set`, `foldl`, and `concat` have already been defi
 The operations are organized as follow:
 * Equality: `beq`, `isEqv`.
 * Lexicographic ordering: `lt`, `le`, and instances.
+* Head and tail operators: `head`, `head?`, `headD?`, `tail`, `tail?`, `tailD`.
 * Basic operations:
-  `map`, `filter`, `filterMap`, `foldr`, `append`, `join`, `pure`, `bind`, `replicate`, and `reverse`.
+  `map`, `filter`, `filterMap`, `foldr`, `append`, `join`, `pure`, `bind`, `replicate`, and
+  `reverse`.
+* Additional functions defined in terms of these: `leftpad`, `rightPad`, and `reduceOption`.
 * List membership: `isEmpty`, `elem`, `contains`, `mem` (and the `∈` notation),
   and decidability for predicates quantifying over membership in a `List`.
 * Sublists: `take`, `drop`, `takeWhile`, `dropWhile`, `partition`, `dropLast`,
-  `isPrefixOf`, `isPrefixOf?`, `isSuffixOf`, `isSuffixOf?`, `Subset`, `Sublist`, `rotateLeft` and `rotateRight`.
-* Manipulating elements: `replace`, `insert`, `erase`, `eraseP`, `eraseIdx`, `find?`, `findSome?`, and `lookup`.
+  `isPrefixOf`, `isPrefixOf?`, `isSuffixOf`, `isSuffixOf?`, `Subset`, `Sublist`,
+  `rotateLeft` and `rotateRight`.
+* Manipulating elements: `replace`, `insert`, `erase`, `eraseP`, `eraseIdx`.
+* Finding elements: `find?`, `findSome?`, `findIdx`, `indexOf`, `findIdx?`, `indexOf?`,
+ `countP`, `count`, and `lookup`.
 * Logic: `any`, `all`, `or`, and `and`.
 * Zippers: `zipWith`, `zip`, `zipWithAll`, and `unzip`.
 * Ranges and enumeration: `range`, `iota`, `enumFrom`, and `enum`.
 * Minima and maxima: `minimum?` and `maximum?`.
-* Other functions: `intersperse`, `intercalate`, `eraseDups`, `eraseReps`, `span`, `groupBy`, `removeAll`
+* Other functions: `intersperse`, `intercalate`, `eraseDups`, `eraseReps`, `span`, `groupBy`,
+  `removeAll`
   (currently these functions are mostly only used in meta code,
   and do not have API suitable for verification).
 
-Further operations are defined in `Init.Data.List.BasicAux` (because they use `Array` in their implementations), namely:
+Further operations are defined in `Init.Data.List.BasicAux`
+(because they use `Array` in their implementations), namely:
 * Variant getters: `get!`, `get?`, `getD`, `getLast`, `getLast!`, `getLast?`, and `getLastD`.
-* Head and tail: `head`, `head!`, `head?`, `headD`, `tail!`, `tail?`, and `tailD`.
+* Head and tail: `head!`, `tail!`.
 * Other operations on sublists: `partitionMap`, `rotateLeft`, and `rotateRight`.
 -/
 
@@ -315,6 +323,16 @@ def headD : (as : List α) → (fallback : α) → α
 @[simp 1100] theorem headD_nil : @headD α [] d = d := rfl
 @[simp 1100] theorem headD_cons : @headD α (a::l) d = a := rfl
 
+/-! ### tail -/
+
+/-- Get the tail of a nonempty list, or return `[]` for `[]`. -/
+def tail : List α → List α
+  | []    => []
+  | _::as => as
+
+@[simp] theorem tail_nil : @tail α [] = [] := rfl
+@[simp] theorem tail_cons : @tail α (a::as) = as := rfl
+
 /-! ### tail? -/
 
 /--
@@ -577,6 +595,28 @@ theorem replicate_succ (a : α) (n) : replicate (n+1) a = a :: replicate n a :=
   | zero => simp
   | succ n ih => simp only [ih, replicate_succ, length_cons, Nat.succ_eq_add_one]
 
+/-! ## Additional functions -/
+
+/-! ### leftpad and rightpad -/
+
+/--
+Pads `l : List α` on the left with repeated occurrences of `a : α` until it is of length `n`.
+If `l` is initially larger than `n`, just return `l`.
+-/
+def leftpad (n : Nat) (a : α) (l : List α) : List α := replicate (n - length l) a ++ l
+
+/--
+Pads `l : List α` on the right with repeated occurrences of `a : α` until it is of length `n`.
+If `l` is initially larger than `n`, just return `l`.
+-/
+def rightpad (n : Nat) (a : α) (l : List α) : List α := l ++ replicate (n - length l) a
+
+/-! ### reduceOption -/
+
+/-- Drop `none`s from a list, and replace each remaining `some a` with `a`. -/
+@[inline] def reduceOption {α} : List (Option α) → List α :=
+  List.filterMap id
+
 /-! ## List membership
 
 * `L.contains a : Bool` determines, using a `[BEq α]` instance, whether `L` contains an element `· == a`.
@@ -719,7 +759,7 @@ def take : Nat → List α → List α
 
 @[simp] theorem take_nil : ([] : List α).take i = [] := by cases i <;> rfl
 @[simp] theorem take_zero (l : List α) : l.take 0 = [] := rfl
-@[simp] theorem take_cons_succ : (a::as).take (i+1) = a :: as.take i := rfl
+@[simp] theorem take_succ_cons : (a::as).take (i+1) = a :: as.take i := rfl
 
 /-! ### drop -/
 
@@ -826,46 +866,6 @@ def dropLast {α} : List α → List α
     have ih := length_dropLast_cons b bs
     simp [dropLast, ih]
 
-/-! ### isPrefixOf -/
-
-/--  `isPrefixOf l₁ l₂` returns `true` Iff `l₁` is a prefix of `l₂`.
-That is, there exists a `t` such that `l₂ == l₁ ++ t`. -/
-def isPrefixOf [BEq α] : List α → List α → Bool
-  | [],    _     => true
-  | _,     []    => false
-  | a::as, b::bs => a == b && isPrefixOf as bs
-
-@[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
-
-/-! ### isPrefixOf? -/
-
-/-- `isPrefixOf? l₁ l₂` returns `some t` when `l₂ == l₁ ++ t`. -/
-def isPrefixOf? [BEq α] : List α → List α → Option (List α)
-  | [], l₂ => some l₂
-  | _, [] => none
-  | (x₁ :: l₁), (x₂ :: l₂) =>
-    if x₁ == x₂ then isPrefixOf? l₁ l₂ else none
-
-/-! ### isSuffixOf -/
-
-/--  `isSuffixOf l₁ l₂` returns `true` Iff `l₁` is a suffix of `l₂`.
-That is, there exists a `t` such that `l₂ == t ++ l₁`. -/
-def isSuffixOf [BEq α] (l₁ l₂ : List α) : Bool :=
-  isPrefixOf l₁.reverse l₂.reverse
-
-@[simp] theorem isSuffixOf_nil_left [BEq α] : isSuffixOf ([] : List α) l = true := by
-  simp [isSuffixOf]
-
-/-! ### isSuffixOf? -/
-
-/-- `isSuffixOf? l₁ l₂` returns `some t` when `l₂ == t ++ l₁`.-/
-def isSuffixOf? [BEq α] (l₁ l₂ : List α) : Option (List α) :=
-  Option.map List.reverse <| isPrefixOf? l₁.reverse l₂.reverse
-
 /-! ### Subset -/
 
 /--
@@ -900,6 +900,88 @@ def isSublist [BEq α] : List α → List α → Bool
     then tl₁.isSublist tl₂
     else l₁.isSublist tl₂
 
+/-! ### IsPrefix / isPrefixOf / isPrefixOf? -/
+
+/--
+`IsPrefix l₁ l₂`, or `l₁ <+: l₂`, means that `l₁` is a prefix of `l₂`,
+that is, `l₂` has the form `l₁ ++ t` for some `t`.
+-/
+def IsPrefix (l₁ : List α) (l₂ : List α) : Prop := Exists fun t => l₁ ++ t = l₂
+
+@[inherit_doc] infixl:50 " <+: " => IsPrefix
+
+/--  `isPrefixOf l₁ l₂` returns `true` Iff `l₁` is a prefix of `l₂`.
+That is, there exists a `t` such that `l₂ == l₁ ++ t`. -/
+def isPrefixOf [BEq α] : List α → List α → Bool
+  | [],    _     => true
+  | _,     []    => false
+  | a::as, b::bs => a == b && isPrefixOf as bs
+
+@[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
+
+/-- `isPrefixOf? l₁ l₂` returns `some t` when `l₂ == l₁ ++ t`. -/
+def isPrefixOf? [BEq α] : List α → List α → Option (List α)
+  | [], l₂ => some l₂
+  | _, [] => none
+  | (x₁ :: l₁), (x₂ :: l₂) =>
+    if x₁ == x₂ then isPrefixOf? l₁ l₂ else none
+
+/-! ### IsSuffix / isSuffixOf / isSuffixOf? -/
+
+/--  `isSuffixOf l₁ l₂` returns `true` Iff `l₁` is a suffix of `l₂`.
+That is, there exists a `t` such that `l₂ == t ++ l₁`. -/
+def isSuffixOf [BEq α] (l₁ l₂ : List α) : Bool :=
+  isPrefixOf l₁.reverse l₂.reverse
+
+@[simp] theorem isSuffixOf_nil_left [BEq α] : isSuffixOf ([] : List α) l = true := by
+  simp [isSuffixOf]
+
+/-- `isSuffixOf? l₁ l₂` returns `some t` when `l₂ == t ++ l₁`.-/
+def isSuffixOf? [BEq α] (l₁ l₂ : List α) : Option (List α) :=
+  Option.map List.reverse <| isPrefixOf? l₁.reverse l₂.reverse
+
+/--
+`IsSuffix l₁ l₂`, or `l₁ <:+ l₂`, means that `l₁` is a suffix of `l₂`,
+that is, `l₂` has the form `t ++ l₁` for some `t`.
+-/
+def IsSuffix (l₁ : List α) (l₂ : List α) : Prop := Exists fun t => t ++ l₁ = l₂
+
+@[inherit_doc] infixl:50 " <:+ " => IsSuffix
+
+/-! ### IsInfix -/
+
+/--
+`IsInfix l₁ l₂`, or `l₁ <:+: l₂`, means that `l₁` is a contiguous
+substring of `l₂`, that is, `l₂` has the form `s ++ l₁ ++ t` for some `s, t`.
+-/
+def IsInfix (l₁ : List α) (l₂ : List α) : Prop := Exists fun s => Exists fun t => s ++ l₁ ++ t = l₂
+
+@[inherit_doc] infixl:50 " <:+: " => IsInfix
+
+/-! ### splitAt -/
+
+/--
+Split a list at an index.
+```
+splitAt 2 [a, b, c] = ([a, b], [c])
+```
+-/
+def splitAt (n : Nat) (l : List α) : List α × List α := go l n [] where
+  /--
+  Auxiliary for `splitAt`:
+  `splitAt.go l xs n acc = (acc.reverse ++ take n xs, drop n xs)` if `n < xs.length`,
+  and `(l, [])` otherwise.
+  -/
+  go : List α → Nat → List α → List α × List α
+  | [], _, _ => (l, []) -- This branch ensures the pointer equality of the result with the input
+                        -- without any runtime branching cost.
+  | x :: xs, n+1, acc => go xs n (x :: acc)
+  | xs, _, acc => (acc.reverse, xs)
+
 /-! ### rotateLeft -/
 
 /--
@@ -1058,6 +1140,8 @@ def eraseIdx : List α → Nat → List α
 @[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
 
+/-! Finding elements -/
+
 /-! ### find? -/
 
 /--
@@ -1095,6 +1179,50 @@ theorem findSome?_cons {f : α → Option β} :
     (a::as).findSome? f = match f a with | some b => some b | none => as.findSome? f :=
   rfl
 
+/-! ### findIdx -/
+
+/-- Returns the index of the first element satisfying `p`, or the length of the list otherwise. -/
+@[inline] def findIdx (p : α → Bool) (l : List α) : Nat := go l 0 where
+  /-- Auxiliary for `findIdx`: `findIdx.go p l n = findIdx p l + n` -/
+  @[specialize] go : List α → Nat → Nat
+  | [], n => n
+  | a :: l, n => bif p a then n else go l (n + 1)
+
+@[simp] theorem findIdx_nil {α : Type _} (p : α → Bool) : [].findIdx p = 0 := rfl
+
+/-! ### indexOf -/
+
+/-- Returns the index of the first element equal to `a`, or the length of the list otherwise. -/
+def indexOf [BEq α] (a : α) : List α → Nat := findIdx (· == a)
+
+@[simp] theorem indexOf_nil [BEq α] : ([] : List α).indexOf x = 0 := rfl
+
+/-! ### findIdx? -/
+
+/-- Return the index of the first occurrence of an element satisfying `p`. -/
+def findIdx? (p : α → Bool) : List α → (start : Nat := 0) → Option Nat
+| [], _ => none
+| a :: l, i => if p a then some i else findIdx? p l (i + 1)
+
+/-! ### indexOf? -/
+
+/-- Return the index of the first occurrence of `a` in the list. -/
+@[inline] def indexOf? [BEq α] (a : α) : List α → Option Nat := findIdx? (· == a)
+
+/-! ### countP -/
+
+/-- `countP p l` is the number of elements of `l` that satisfy `p`. -/
+@[inline] def countP (p : α → Bool) (l : List α) : Nat := go l 0 where
+  /-- Auxiliary for `countP`: `countP.go p l acc = countP p l + acc`. -/
+  @[specialize] go : List α → Nat → Nat
+  | [], acc => acc
+  | x :: xs, acc => bif p x then go xs (acc + 1) else go xs acc
+
+/-! ### count -/
+
+/-- `count a l` is the number of occurrences of `a` in `l`. -/
+@[inline] def count [BEq α] (a : α) : List α → Nat := countP (· == a)
+
 /-! ### lookup -/
 
 /--
@@ -1115,6 +1243,36 @@ theorem lookup_cons [BEq α] {k : α} :
     ((k,b)::es).lookup a = match a == k with | true => some b | false => es.lookup a :=
   rfl
 
+/-! ## Permutations -/
+
+/-! ### Perm -/
+
+/--
+`Perm l₁ l₂` or `l₁ ~ l₂` asserts that `l₁` and `l₂` are permutations
+of each other. This is defined by induction using pairwise swaps.
+-/
+inductive Perm : List α → List α → Prop
+  /-- `[] ~ []` -/
+  | nil : Perm [] []
+  /-- `l₁ ~ l₂ → x::l₁ ~ x::l₂` -/
+  | cons (x : α) {l₁ l₂ : List α} : Perm l₁ l₂ → Perm (x :: l₁) (x :: l₂)
+  /-- `x::y::l ~ y::x::l` -/
+  | swap (x y : α) (l : List α) : Perm (y :: x :: l) (x :: y :: l)
+  /-- `Perm` is transitive. -/
+  | trans {l₁ l₂ l₃ : List α} : Perm l₁ l₂ → Perm l₂ l₃ → Perm l₁ l₃
+
+@[inherit_doc] scoped infixl:50 " ~ " => Perm
+
+/-! ### isPerm -/
+
+/--
+`O(|l₁| * |l₂|)`. Computes whether `l₁` is a permutation of `l₂`. See `isPerm_iff` for a
+characterization in terms of `List.Perm`.
+-/
+def isPerm [BEq α] : List α → List α → Bool
+  | [], l₂ => l₂.isEmpty
+  | a :: l₁, l₂ => l₂.contains a && l₁.isPerm (l₂.erase a)
+
 /-! ## Logical operations -/
 
 /-! ### any -/
@@ -1236,6 +1394,14 @@ def unzip : List (α × β) → List α × List β
 
 /-! ## Ranges and enumeration -/
 
+/-- Sum of a list of natural numbers. -/
+-- This is not in the `List` namespace as later `List.sum` will be defined polymorphically.
+protected def _root_.Nat.sum (l : List Nat) : Nat := l.foldr (·+·) 0
+
+@[simp] theorem _root_.Nat.sum_nil : Nat.sum ([] : List Nat) = 0 := rfl
+@[simp] theorem _root_.Nat.sum_cons (a : Nat) (l : List Nat) :
+    Nat.sum (a::l) = a + Nat.sum l := rfl
+
 /-! ### range -/
 
 /--
@@ -1251,6 +1417,14 @@ where
 
 @[simp] theorem range_zero : range 0 = [] := rfl
 
+/-! ### range' -/
+
+/-- `range' start len step` is the list of numbers `[start, start+step, ..., start+(len-1)*step]`.
+  It is intended mainly for proving properties of `range` and `iota`. -/
+def range' : (start len : Nat) → (step : Nat := 1) → List Nat
+  | _, 0, _ => []
+  | s, n+1, step => s :: range' (s+step) n step
+
 /-! ### iota -/
 
 /--

src/Init/Data/List/BasicAux.lean

@@ -192,7 +192,7 @@ macro "sizeOf_list_dec" : tactic =>
   `(tactic| first
     | with_reducible apply sizeOf_lt_of_mem; assumption; done
     | with_reducible
-        apply Nat.lt_trans (sizeOf_lt_of_mem ?h)
+        apply Nat.lt_of_lt_of_le (sizeOf_lt_of_mem ?h)
         case' h => assumption
       simp_arith)
 

src/Init/Data/List/Control.lean

@@ -127,12 +127,12 @@ 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
-    | [],     bs => pure bs
+    | [],     bs => pure bs.reverse
     | a :: as, bs => do
       match (← f a) with
       | none   => loop as bs
       | some b => loop as (b::bs)
-  loop as.reverse []
+  loop as []
 
 /--
 Folds a monadic function over a list from left to right:
@@ -227,6 +227,8 @@ def findSomeM? {m : Type u → Type v} [Monad m] {α : Type w} {β : Type u} (f
 instance : ForIn m (List α) α where
   forIn := List.forIn
 
+@[simp] theorem forIn_eq_forIn [Monad m] : @List.forIn α β m _ = forIn := rfl
+
 @[simp] theorem forIn_nil [Monad m] (f : α → β → m (ForInStep β)) (b : β) : forIn [] b f = pure b :=
   rfl
 

src/Init/Data/List/Count.lean

@@ -0,0 +1,250 @@
+/-
+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.Sublist
+
+/-!
+# Lemmas about `List.countP` and `List.count`.
+-/
+
+namespace List
+
+open Nat
+
+/-! ### countP -/
+section countP
+
+variable (p q : α → Bool)
+
+@[simp] theorem countP_nil : countP p [] = 0 := rfl
+
+protected theorem countP_go_eq_add (l) : countP.go p l n = n + countP.go p l 0 := by
+  induction l generalizing n with
+  | nil => rfl
+  | cons head tail ih =>
+    unfold countP.go
+    rw [ih (n := n + 1), ih (n := n), ih (n := 1)]
+    if h : p head then simp [h, Nat.add_assoc] else simp [h]
+
+@[simp] theorem countP_cons_of_pos (l) (pa : p a) : countP p (a :: l) = countP p l + 1 := by
+  have : countP.go p (a :: l) 0 = countP.go p l 1 := show cond .. = _ by rw [pa]; rfl
+  unfold countP
+  rw [this, Nat.add_comm, List.countP_go_eq_add]
+
+@[simp] theorem countP_cons_of_neg (l) (pa : ¬p a) : countP p (a :: l) = countP p l := by
+  simp [countP, countP.go, pa]
+
+theorem countP_cons (a : α) (l) : countP p (a :: l) = countP p l + if p a then 1 else 0 := by
+  by_cases h : p a <;> simp [h]
+
+theorem length_eq_countP_add_countP (l) : length l = countP p l + countP (fun a => ¬p a) l := by
+  induction l with
+  | nil => rfl
+  | cons x h ih =>
+    if h : p x then
+      rw [countP_cons_of_pos _ _ h, countP_cons_of_neg _ _ _, length, ih]
+      · rw [Nat.add_assoc, Nat.add_comm _ 1, Nat.add_assoc]
+      · simp only [h, not_true_eq_false, decide_False, not_false_eq_true]
+    else
+      rw [countP_cons_of_pos (fun a => ¬p a) _ _, countP_cons_of_neg _ _ h, length, ih]
+      · rfl
+      · simp only [h, not_false_eq_true, decide_True]
+
+theorem countP_eq_length_filter (l) : countP p l = length (filter p l) := by
+  induction l with
+  | nil => rfl
+  | cons x l ih =>
+    if h : p x
+    then rw [countP_cons_of_pos p l h, ih, filter_cons_of_pos h, length]
+    else rw [countP_cons_of_neg p l h, ih, filter_cons_of_neg h]
+
+theorem countP_le_length : countP p l ≤ l.length := by
+  simp only [countP_eq_length_filter]
+  apply length_filter_le
+
+@[simp] theorem countP_append (l₁ l₂) : countP p (l₁ ++ l₂) = countP p l₁ + countP p l₂ := by
+  simp only [countP_eq_length_filter, filter_append, length_append]
+
+theorem countP_pos : 0 < countP p l ↔ ∃ a ∈ l, p a := by
+  simp only [countP_eq_length_filter, length_pos_iff_exists_mem, mem_filter, exists_prop]
+
+theorem countP_eq_zero : countP p l = 0 ↔ ∀ a ∈ l, ¬p a := by
+  simp only [countP_eq_length_filter, length_eq_zero, filter_eq_nil]
+
+theorem countP_eq_length : countP p l = l.length ↔ ∀ a ∈ l, p a := by
+  rw [countP_eq_length_filter, filter_length_eq_length]
+
+theorem Sublist.countP_le (s : l₁ <+ l₂) : countP p l₁ ≤ countP p l₂ := by
+  simp only [countP_eq_length_filter]
+  apply s.filter _ |>.length_le
+
+theorem IsPrefix.countP_le (s : l₁ <+: l₂) : countP p l₁ ≤ countP p l₂ := s.sublist.countP_le _
+theorem IsSuffix.countP_le (s : l₁ <:+ l₂) : countP p l₁ ≤ countP p l₂ := s.sublist.countP_le _
+theorem IsInfix.countP_le (s : l₁ <:+: l₂) : countP p l₁ ≤ countP p l₂ := s.sublist.countP_le _
+
+theorem countP_filter (l : List α) :
+    countP p (filter q l) = countP (fun a => p a ∧ q a) l := by
+  simp only [countP_eq_length_filter, filter_filter]
+
+@[simp] theorem countP_true {l : List α} : (l.countP fun _ => true) = l.length := by
+  rw [countP_eq_length]
+  simp
+
+@[simp] theorem countP_false {l : List α} : (l.countP fun _ => false) = 0 := by
+  rw [countP_eq_zero]
+  simp
+
+@[simp] theorem countP_map (p : β → Bool) (f : α → β) :
+    ∀ l, countP p (map f l) = countP (p ∘ f) l
+  | [] => rfl
+  | a :: l => by rw [map_cons, countP_cons, countP_cons, countP_map p f l]; rfl
+
+variable {p q}
+
+theorem countP_mono_left (h : ∀ x ∈ l, p x → q x) : countP p l ≤ countP q l := by
+  induction l with
+  | nil => apply Nat.le_refl
+  | cons a l ihl =>
+    rw [forall_mem_cons] at h
+    have ⟨ha, hl⟩ := h
+    simp [countP_cons]
+    cases h : p a
+    · simp only [Bool.false_eq_true, ↓reduceIte, Nat.add_zero]
+      apply Nat.le_trans ?_ (Nat.le_add_right _ _)
+      apply ihl hl
+    · simp only [↓reduceIte, ha h, succ_le_succ_iff]
+      apply ihl hl
+
+theorem countP_congr (h : ∀ x ∈ l, p x ↔ q x) : countP p l = countP q l :=
+  Nat.le_antisymm
+    (countP_mono_left fun x hx => (h x hx).1)
+    (countP_mono_left fun x hx => (h x hx).2)
+
+end countP
+
+/-! ### count -/
+section count
+
+variable [BEq α]
+
+@[simp] theorem count_nil (a : α) : count a [] = 0 := rfl
+
+theorem count_cons (a b : α) (l : List α) :
+    count a (b :: l) = count a l + if b == a then 1 else 0 := by
+  simp [count, countP_cons]
+
+theorem count_tail : ∀ (l : List α) (a : α) (h : l ≠ []),
+      l.tail.count a = l.count a - if l.head h == a then 1 else 0
+  | head :: tail, a, _ => by simp [count_cons]
+
+theorem count_le_length (a : α) (l : List α) : count a l ≤ l.length := countP_le_length _
+
+theorem Sublist.count_le (h : l₁ <+ l₂) (a : α) : count a l₁ ≤ count a l₂ := h.countP_le _
+
+theorem IsPrefix.count_le (h : l₁ <+: l₂) (a : α) : count a l₁ ≤ count a l₂ := h.sublist.count_le _
+theorem IsSuffix.count_le (h : l₁ <:+ l₂) (a : α) : count a l₁ ≤ count a l₂ := h.sublist.count_le _
+theorem IsInfix.count_le (h : l₁ <:+: l₂) (a : α) : count a l₁ ≤ count a l₂ := h.sublist.count_le _
+
+theorem count_le_count_cons (a b : α) (l : List α) : count a l ≤ count a (b :: l) :=
+  (sublist_cons_self _ _).count_le _
+
+theorem count_singleton (a b : α) : count a [b] = if b == a then 1 else 0 := by
+  simp [count_cons]
+
+@[simp] theorem count_append (a : α) : ∀ l₁ l₂, count a (l₁ ++ l₂) = count a l₁ + count a l₂ :=
+  countP_append _
+
+variable [LawfulBEq α]
+
+@[simp] theorem count_cons_self (a : α) (l : List α) : count a (a :: l) = count a l + 1 := by
+  simp [count_cons]
+
+@[simp] theorem count_cons_of_ne (h : a ≠ b) (l : List α) : count a (b :: l) = count a l := by
+  simp only [count_cons, cond_eq_if, beq_iff_eq]
+  split <;> simp_all
+
+theorem count_singleton_self (a : α) : count a [a] = 1 := by simp
+
+theorem count_concat_self (a : α) (l : List α) :
+    count a (concat l a) = (count a l) + 1 := by simp
+
+@[simp]
+theorem count_pos_iff_mem {a : α} {l : List α} : 0 < count a l ↔ a ∈ l := by
+  simp only [count, countP_pos, beq_iff_eq, exists_eq_right]
+
+theorem count_eq_zero_of_not_mem {a : α} {l : List α} (h : a ∉ l) : count a l = 0 :=
+  Decidable.byContradiction fun h' => h <| count_pos_iff_mem.1 (Nat.pos_of_ne_zero h')
+
+theorem not_mem_of_count_eq_zero {a : α} {l : List α} (h : count a l = 0) : a ∉ l :=
+  fun h' => Nat.ne_of_lt (count_pos_iff_mem.2 h') h.symm
+
+theorem count_eq_zero {l : List α} : count a l = 0 ↔ a ∉ l :=
+  ⟨not_mem_of_count_eq_zero, count_eq_zero_of_not_mem⟩
+
+theorem count_eq_length {l : List α} : count a l = l.length ↔ ∀ b ∈ l, a = b := by
+  rw [count, countP_eq_length]
+  refine ⟨fun h b hb => Eq.symm ?_, fun h b hb => ?_⟩
+  · simpa using h b hb
+  · rw [h b hb, beq_self_eq_true]
+
+@[simp] theorem count_replicate_self (a : α) (n : Nat) : count a (replicate n a) = n :=
+  (count_eq_length.2 <| fun _ h => (eq_of_mem_replicate h).symm).trans (length_replicate ..)
+
+theorem count_replicate (a b : α) (n : Nat) : count a (replicate n b) = if b == a then n else 0 := by
+  split <;> (rename_i h; simp only [beq_iff_eq] at h)
+  · exact ‹b = a› ▸ count_replicate_self ..
+  · exact count_eq_zero.2 <| mt eq_of_mem_replicate (Ne.symm h)
+
+theorem filter_beq (l : List α) (a : α) : l.filter (· == a) = replicate (count a l) a := by
+  simp only [count, countP_eq_length_filter, eq_replicate, mem_filter, beq_iff_eq]
+  exact ⟨trivial, fun _ h => h.2⟩
+
+theorem filter_eq {α} [DecidableEq α] (l : List α) (a : α) : l.filter (· = a) = replicate (count a l) a :=
+  filter_beq l a
+
+theorem le_count_iff_replicate_sublist {l : List α} : n ≤ count a l ↔ replicate n a <+ l := by
+  refine ⟨fun h => ?_, fun h => ?_⟩
+  · exact ((replicate_sublist_replicate a).2 h).trans <| filter_beq l a ▸ filter_sublist _
+  · simpa only [count_replicate_self] using h.count_le a
+
+theorem replicate_count_eq_of_count_eq_length {l : List α} (h : count a l = length l) :
+    replicate (count a l) a = l :=
+  (le_count_iff_replicate_sublist.mp (Nat.le_refl _)).eq_of_length <|
+    (length_replicate (count a l) a).trans h
+
+@[simp] theorem count_filter {l : List α} (h : p a) : count a (filter p l) = count a l := by
+  rw [count, countP_filter]; congr; funext b
+  simp; rintro rfl; exact h
+
+theorem count_le_count_map [DecidableEq β] (l : List α) (f : α → β) (x : α) :
+    count x l ≤ count (f x) (map f l) := by
+  rw [count, count, countP_map]
+  apply countP_mono_left; simp (config := { contextual := true })
+
+theorem count_erase (a b : α) :
+    ∀ l : List α, count a (l.erase b) = count a l - if b == a then 1 else 0
+  | [] => by simp
+  | c :: l => by
+    rw [erase_cons]
+    if hc : c = b then
+      have hc_beq := (beq_iff_eq _ _).mpr hc
+      rw [if_pos hc_beq, hc, count_cons, Nat.add_sub_cancel]
+    else
+      have hc_beq := beq_false_of_ne hc
+      simp only [hc_beq, if_false, count_cons, count_cons, count_erase a b l]
+      if ha : b = a then
+        rw [ha, eq_comm] at hc
+        rw [if_pos ((beq_iff_eq _ _).2 ha), if_neg (by simpa using Ne.symm hc), Nat.add_zero, Nat.add_zero]
+      else
+        rw [if_neg (by simpa using ha), Nat.sub_zero, Nat.sub_zero]
+
+@[simp] theorem count_erase_self (a : α) (l : List α) :
+    count a (List.erase l a) = count a l - 1 := by rw [count_erase, if_pos (by simp)]
+
+@[simp] theorem count_erase_of_ne (ab : a ≠ b) (l : List α) : count a (l.erase b) = count a l := by
+  rw [count_erase, if_neg (by simpa using ab.symm), Nat.sub_zero]
+
+end count

src/Init/Data/List/Erase.lean

@@ -0,0 +1,457 @@
+/-
+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,
+  Yury Kudryashov
+-/
+prelude
+import Init.Data.List.Pairwise
+
+/-!
+# Lemmas about `List.eraseP` and `List.erase`.
+-/
+
+namespace List
+
+open Nat
+
+/-! ### eraseP -/
+
+@[simp] theorem eraseP_nil : [].eraseP p = [] := rfl
+
+theorem eraseP_cons (a : α) (l : List α) :
+    (a :: l).eraseP p = bif p a then l else a :: l.eraseP p := rfl
+
+@[simp] theorem eraseP_cons_of_pos {l : List α} {p} (h : p a) : (a :: l).eraseP p = l := by
+  simp [eraseP_cons, h]
+
+@[simp] theorem eraseP_cons_of_neg {l : List α} {p} (h : ¬p a) :
+    (a :: l).eraseP p = a :: l.eraseP p := by simp [eraseP_cons, h]
+
+theorem eraseP_of_forall_not {l : List α} (h : ∀ a, a ∈ l → ¬p a) : l.eraseP p = l := by
+  induction l with
+  | nil => rfl
+  | cons _ _ ih => simp [h _ (.head ..), ih (forall_mem_cons.1 h).2]
+
+theorem exists_of_eraseP : ∀ {l : List α} {a} (al : a ∈ l) (pa : p a),
+    ∃ a l₁ l₂, (∀ b ∈ l₁, ¬p b) ∧ p a ∧ l = l₁ ++ a :: l₂ ∧ l.eraseP p = l₁ ++ l₂
+  | b :: l, a, al, pa =>
+    if pb : p b then
+      ⟨b, [], l, forall_mem_nil _, pb, by simp [pb]⟩
+    else
+      match al with
+      | .head .. => nomatch pb pa
+      | .tail _ al =>
+        let ⟨c, l₁, l₂, h₁, h₂, h₃, h₄⟩ := exists_of_eraseP al pa
+        ⟨c, b::l₁, l₂, (forall_mem_cons ..).2 ⟨pb, h₁⟩,
+          h₂, by rw [h₃, cons_append], by simp [pb, h₄]⟩
+
+theorem exists_or_eq_self_of_eraseP (p) (l : List α) :
+    l.eraseP p = l ∨
+    ∃ a l₁ l₂, (∀ b ∈ l₁, ¬p b) ∧ p a ∧ l = l₁ ++ a :: l₂ ∧ l.eraseP p = l₁ ++ l₂ :=
+  if h : ∃ a ∈ l, p a then
+    let ⟨_, ha, pa⟩ := h
+    .inr (exists_of_eraseP ha pa)
+  else
+    .inl (eraseP_of_forall_not (h ⟨·, ·, ·⟩))
+
+@[simp] theorem length_eraseP_of_mem (al : a ∈ l) (pa : p a) :
+    length (l.eraseP p) = length l - 1 := by
+  let ⟨_, l₁, l₂, _, _, e₁, e₂⟩ := exists_of_eraseP al pa
+  rw [e₂]; simp [length_append, e₁]; rfl
+
+theorem length_eraseP {l : List α} : (l.eraseP p).length = if l.any p then l.length - 1 else l.length := by
+  split <;> rename_i h
+  · simp only [any_eq_true] at h
+    obtain ⟨x, m, h⟩ := h
+    simp [length_eraseP_of_mem m h]
+  · simp only [any_eq_true] at h
+    rw [eraseP_of_forall_not]
+    simp_all
+
+theorem eraseP_sublist (l : List α) : l.eraseP p <+ l := by
+  match exists_or_eq_self_of_eraseP p l with
+  | .inl h => rw [h]; apply Sublist.refl
+  | .inr ⟨c, l₁, l₂, _, _, h₃, h₄⟩ => rw [h₄, h₃]; simp
+
+theorem eraseP_subset (l : List α) : l.eraseP p ⊆ l := (eraseP_sublist l).subset
+
+protected theorem Sublist.eraseP : l₁ <+ l₂ → l₁.eraseP p <+ l₂.eraseP p
+  | .slnil => Sublist.refl _
+  | .cons a s => by
+    by_cases h : p a
+    · simpa [h] using s.eraseP.trans (eraseP_sublist _)
+    · simpa [h] using s.eraseP.cons _
+  | .cons₂ a s => by
+    by_cases h : p a
+    · simpa [h] using s
+    · simpa [h] using s.eraseP
+
+theorem length_eraseP_le (l : List α) : (l.eraseP p).length ≤ l.length :=
+  l.eraseP_sublist.length_le
+
+theorem mem_of_mem_eraseP {l : List α} : a ∈ l.eraseP p → a ∈ l := (eraseP_subset _ ·)
+
+@[simp] theorem mem_eraseP_of_neg {l : List α} (pa : ¬p a) : a ∈ l.eraseP p ↔ a ∈ l := by
+  refine ⟨mem_of_mem_eraseP, fun al => ?_⟩
+  match exists_or_eq_self_of_eraseP p l with
+  | .inl h => rw [h]; assumption
+  | .inr ⟨c, l₁, l₂, h₁, h₂, h₃, h₄⟩ =>
+    rw [h₄]; rw [h₃] at al
+    have : a ≠ c := fun h => (h ▸ pa).elim h₂
+    simp [this] at al; simp [al]
+
+@[simp] theorem eraseP_eq_self_iff {p} {l : List α} : l.eraseP p = l ↔ ∀ a ∈ l, ¬ p a := by
+  rw [← Sublist.length_eq (eraseP_sublist l), length_eraseP]
+  split <;> rename_i h
+  · simp only [any_eq_true, length_eq_zero] at h
+    constructor
+    · intro; simp_all [Nat.sub_one_eq_self]
+    · intro; obtain ⟨x, m, h⟩ := h; simp_all
+  · simp_all
+
+theorem eraseP_map (f : β → α) : ∀ (l : List β), (map f l).eraseP p = map f (l.eraseP (p ∘ f))
+  | [] => rfl
+  | b::l => by by_cases h : p (f b) <;> simp [h, eraseP_map f l, eraseP_cons_of_pos]
+
+theorem eraseP_filterMap (f : α → Option β) : ∀ (l : List α),
+    (filterMap f l).eraseP p = filterMap f (l.eraseP (fun x => match f x with | some y => p y | none => false))
+  | [] => rfl
+  | a::l => by
+    rw [filterMap_cons, eraseP_cons]
+    split <;> rename_i h
+    · simp [h, eraseP_filterMap]
+    · rename_i b
+      rw [h, eraseP_cons]
+      by_cases w : p b
+      · simp [w]
+      · simp only [w, cond_false]
+        rw [filterMap_cons_some h, eraseP_filterMap]
+
+theorem eraseP_filter (f : α → Bool) (l : List α) :
+    (filter f l).eraseP p = filter f (l.eraseP (fun x => p x && f x)) := by
+  rw [← filterMap_eq_filter, eraseP_filterMap]
+  congr
+  ext x
+  simp only [Option.guard]
+  split <;> split at * <;> simp_all
+
+theorem eraseP_append_left {a : α} (pa : p a) :
+    ∀ {l₁ : List α} l₂, a ∈ l₁ → (l₁++l₂).eraseP p = l₁.eraseP p ++ l₂
+  | x :: xs, l₂, h => by
+    by_cases h' : p x <;> simp [h']
+    rw [eraseP_append_left pa l₂ ((mem_cons.1 h).resolve_left (mt _ h'))]
+    intro | rfl => exact pa
+
+theorem eraseP_append_right :
+    ∀ {l₁ : List α} l₂, (∀ b ∈ l₁, ¬p b) → eraseP p (l₁++l₂) = l₁ ++ l₂.eraseP p
+  | [],      l₂, _ => rfl
+  | x :: xs, l₂, h => by
+    simp [(forall_mem_cons.1 h).1, eraseP_append_right _ (forall_mem_cons.1 h).2]
+
+theorem eraseP_append (l₁ l₂ : List α) :
+    (l₁ ++ l₂).eraseP p = if l₁.any p then l₁.eraseP p ++ l₂ else l₁ ++ l₂.eraseP p := by
+  split <;> rename_i h
+  · simp only [any_eq_true] at h
+    obtain ⟨x, m, h⟩ := h
+    rw [eraseP_append_left h _ m]
+  · simp only [any_eq_true] at h
+    rw [eraseP_append_right _]
+    simp_all
+
+protected theorem IsPrefix.eraseP (h : l₁ <+: l₂) : l₁.eraseP p <+: l₂.eraseP p := by
+  rw [IsPrefix] at h
+  obtain ⟨t, rfl⟩ := h
+  rw [eraseP_append]
+  split
+  · exact prefix_append (eraseP p l₁) t
+  · rw [eraseP_of_forall_not (by simp_all)]
+    exact prefix_append l₁ (eraseP p t)
+
+theorem eraseP_eq_iff {p} {l : List α} :
+    l.eraseP p = l' ↔
+      ((∀ a ∈ l, ¬ p a) ∧ l = l') ∨
+        ∃ a l₁ l₂, (∀ b ∈ l₁, ¬ p b) ∧ p a ∧ l = l₁ ++ a :: l₂ ∧ l' = l₁ ++ l₂ := by
+  cases exists_or_eq_self_of_eraseP p l with
+  | inl h =>
+    constructor
+    · intro h'
+      left
+      exact ⟨eraseP_eq_self_iff.1 h, by simp_all⟩
+    · rintro (⟨-, rfl⟩ | ⟨a, l₁, l₂, h₁, h₂, rfl, rfl⟩)
+      · assumption
+      · rw [eraseP_append_right _ h₁, eraseP_cons_of_pos h₂]
+  | inr h =>
+    obtain ⟨a, l₁, l₂, h₁, h₂, w₁, w₂⟩ := h
+    rw [w₂]
+    subst w₁
+    constructor
+    · rintro rfl
+      right
+      refine ⟨a, l₁, l₂, ?_⟩
+      simp_all
+    · rintro (h | h)
+      · simp_all
+      · obtain ⟨a', l₁', l₂', h₁', h₂', h, rfl⟩ := h
+        have p : l₁ = l₁' := by
+          have q : l₁ = takeWhile (fun x => !p x) (l₁ ++ a :: l₂) := by
+            rw [takeWhile_append_of_pos (by simp_all),
+              takeWhile_cons_of_neg (by simp [h₂]), append_nil]
+          have q' : l₁' = takeWhile (fun x => !p x) (l₁' ++ a' :: l₂') := by
+            rw [takeWhile_append_of_pos (by simpa using h₁'),
+              takeWhile_cons_of_neg (by simp [h₂']), append_nil]
+          simp [h] at q
+          rw [q', q]
+        subst p
+        simp_all
+
+@[simp] theorem eraseP_replicate_of_pos {n : Nat} {a : α} (h : p a) :
+    (replicate n a).eraseP p = replicate (n - 1) a := by
+  cases n <;> simp [replicate_succ, h]
+
+@[simp] theorem eraseP_replicate_of_neg {n : Nat} {a : α} (h : ¬p a) :
+    (replicate n a).eraseP p = replicate n a := by
+  rw [eraseP_of_forall_not (by simp_all)]
+
+theorem Nodup.eraseP (p) : Nodup l → Nodup (l.eraseP p) :=
+  Nodup.sublist <| eraseP_sublist _
+
+theorem eraseP_comm {l : List α} (h : ∀ a ∈ l, ¬ p a ∨ ¬ q a) :
+    (l.eraseP p).eraseP q = (l.eraseP q).eraseP p := by
+  induction l with
+  | nil => rfl
+  | cons a l ih =>
+    simp only [eraseP_cons]
+    by_cases h₁ : p a
+    · by_cases h₂ : q a
+      · simp_all
+      · simp [h₁, h₂, ih (fun b m => h b (mem_cons_of_mem _ m))]
+    · by_cases h₂ : q a
+      · simp [h₁, h₂, ih (fun b m => h b (mem_cons_of_mem _ m))]
+      · simp [h₁, h₂, ih (fun b m => h b (mem_cons_of_mem _ m))]
+
+/-! ### erase -/
+section erase
+variable [BEq α]
+
+@[simp] theorem erase_cons_head [LawfulBEq α] (a : α) (l : List α) : (a :: l).erase a = l := by
+  simp [erase_cons]
+
+@[simp] theorem erase_cons_tail {a b : α} {l : List α} (h : ¬(b == a)) :
+    (b :: l).erase a = b :: l.erase a := by simp only [erase_cons, if_neg h]
+
+theorem erase_of_not_mem [LawfulBEq α] {a : α} : ∀ {l : List α}, a ∉ l → l.erase a = l
+  | [], _ => rfl
+  | b :: l, h => by
+    rw [mem_cons, not_or] at h
+    simp only [erase_cons, if_neg, erase_of_not_mem h.2, beq_iff_eq, Ne.symm h.1, not_false_eq_true]
+
+theorem erase_eq_eraseP' (a : α) (l : List α) : l.erase a = l.eraseP (· == a) := by
+  induction l
+  · simp
+  · next b t ih =>
+    rw [erase_cons, eraseP_cons, ih]
+    if h : b == a then simp [h] else simp [h]
+
+theorem erase_eq_eraseP [LawfulBEq α] (a : α) : ∀ l : List α,  l.erase a = l.eraseP (a == ·)
+  | [] => rfl
+  | b :: l => by
+    if h : a = b then simp [h] else simp [h, Ne.symm h, erase_eq_eraseP a l]
+
+theorem exists_erase_eq [LawfulBEq α] {a : α} {l : List α} (h : a ∈ l) :
+    ∃ l₁ l₂, a ∉ l₁ ∧ l = l₁ ++ a :: l₂ ∧ l.erase a = l₁ ++ l₂ := by
+  let ⟨_, l₁, l₂, h₁, e, h₂, h₃⟩ := exists_of_eraseP h (beq_self_eq_true _)
+  rw [erase_eq_eraseP]; exact ⟨l₁, l₂, fun h => h₁ _ h (beq_self_eq_true _), eq_of_beq e ▸ h₂, h₃⟩
+
+@[simp] theorem length_erase_of_mem [LawfulBEq α] {a : α} {l : List α} (h : a ∈ l) :
+    length (l.erase a) = length l - 1 := by
+  rw [erase_eq_eraseP]; exact length_eraseP_of_mem h (beq_self_eq_true a)
+
+theorem length_erase [LawfulBEq α] (a : α) (l : List α) :
+    length (l.erase a) = if a ∈ l then length l - 1 else length l := by
+  rw [erase_eq_eraseP, length_eraseP]
+  split <;> split <;> simp_all
+
+theorem erase_sublist (a : α) (l : List α) : l.erase a <+ l :=
+  erase_eq_eraseP' a l ▸ eraseP_sublist ..
+
+theorem erase_subset (a : α) (l : List α) : l.erase a ⊆ l := (erase_sublist a l).subset
+
+theorem Sublist.erase (a : α) {l₁ l₂ : List α} (h : l₁ <+ l₂) : l₁.erase a <+ l₂.erase a := by
+  simp only [erase_eq_eraseP']; exact h.eraseP
+
+theorem IsPrefix.erase (a : α) {l₁ l₂ : List α} (h : l₁ <+: l₂) : l₁.erase a <+: l₂.erase a := by
+  simp only [erase_eq_eraseP']; exact h.eraseP
+
+theorem length_erase_le (a : α) (l : List α) : (l.erase a).length ≤ l.length :=
+  (erase_sublist a l).length_le
+
+theorem mem_of_mem_erase {a b : α} {l : List α} (h : a ∈ l.erase b) : a ∈ l := erase_subset _ _ h
+
+@[simp] theorem mem_erase_of_ne [LawfulBEq α] {a b : α} {l : List α} (ab : a ≠ b) :
+    a ∈ l.erase b ↔ a ∈ l :=
+  erase_eq_eraseP b l ▸ mem_eraseP_of_neg (mt eq_of_beq ab.symm)
+
+@[simp] theorem erase_eq_self_iff [LawfulBEq α] {l : List α} : l.erase a = l ↔ a ∉ l := by
+  rw [erase_eq_eraseP', eraseP_eq_self_iff]
+  simp
+
+theorem erase_filter [LawfulBEq α] (f : α → Bool) (l : List α) :
+    (filter f l).erase a = filter f (l.erase a) := by
+  induction l with
+  | nil => rfl
+  | cons x xs ih =>
+    by_cases h : a = x
+    · rw [erase_cons]
+      simp only [h, beq_self_eq_true, ↓reduceIte]
+      rw [filter_cons]
+      split
+      · rw [erase_cons_head]
+      · rw [erase_of_not_mem]
+        simp_all [mem_filter]
+    · rw [erase_cons_tail (by simpa using Ne.symm h), filter_cons, filter_cons]
+      split
+      · rw [erase_cons_tail (by simpa using Ne.symm h), ih]
+      · rw [ih]
+
+theorem erase_append_left [LawfulBEq α] {l₁ : List α} (l₂) (h : a ∈ l₁) :
+    (l₁ ++ l₂).erase a = l₁.erase a ++ l₂ := by
+  simp [erase_eq_eraseP]; exact eraseP_append_left (beq_self_eq_true a) l₂ h
+
+theorem erase_append_right [LawfulBEq α] {a : α} {l₁ : List α} (l₂ : List α) (h : a ∉ l₁) :
+    (l₁ ++ l₂).erase a = (l₁ ++ l₂.erase a) := by
+  rw [erase_eq_eraseP, erase_eq_eraseP, eraseP_append_right]
+  intros b h' h''; rw [eq_of_beq h''] at h; exact h h'
+
+theorem erase_append [LawfulBEq α] {a : α} {l₁ l₂ : List α} :
+    (l₁ ++ l₂).erase a = if a ∈ l₁ then l₁.erase a ++ l₂ else l₁ ++ l₂.erase a := by
+  simp [erase_eq_eraseP, eraseP_append]
+
+theorem erase_comm [LawfulBEq α] (a b : α) (l : List α) :
+    (l.erase a).erase b = (l.erase b).erase a := by
+  if ab : a == b then rw [eq_of_beq ab] else ?_
+  if ha : a ∈ l then ?_ else
+    simp only [erase_of_not_mem ha, erase_of_not_mem (mt mem_of_mem_erase ha)]
+  if hb : b ∈ l then ?_ else
+    simp only [erase_of_not_mem hb, erase_of_not_mem (mt mem_of_mem_erase hb)]
+  match l, l.erase a, exists_erase_eq ha with
+  | _, _, ⟨l₁, l₂, ha', rfl, rfl⟩ =>
+    if h₁ : b ∈ l₁ then
+      rw [erase_append_left _ h₁, erase_append_left _ h₁,
+          erase_append_right _ (mt mem_of_mem_erase ha'), erase_cons_head]
+    else
+      rw [erase_append_right _ h₁, erase_append_right _ h₁, erase_append_right _ ha',
+          erase_cons_tail ab, erase_cons_head]
+
+theorem erase_eq_iff [LawfulBEq α] {a : α} {l : List α} :
+    l.erase a = l' ↔
+      (a ∉ l ∧ l = l') ∨
+        ∃ l₁ l₂, a ∉ l₁ ∧ l = l₁ ++ a :: l₂ ∧ l' = l₁ ++ l₂ := by
+  rw [erase_eq_eraseP', eraseP_eq_iff]
+  simp only [beq_iff_eq, forall_mem_ne', exists_and_left]
+  constructor
+  · rintro (⟨h, rfl⟩ | ⟨a', l', h, rfl, x, rfl, rfl⟩)
+    · left; simp_all
+    · right; refine ⟨l', h, x, by simp⟩
+  · rintro (⟨h, rfl⟩ | ⟨l₁, h, x, rfl, rfl⟩)
+    · left; simp_all
+    · right; refine ⟨a, l₁, h, by simp⟩
+
+@[simp] theorem erase_replicate_self [LawfulBEq α] {a : α} :
+    (replicate n a).erase a = replicate (n - 1) a := by
+  cases n <;> simp [replicate_succ]
+
+@[simp] theorem erase_replicate_ne [LawfulBEq α] {a b : α} (h : !b == a) :
+    (replicate n a).erase b = replicate n a := by
+  rw [erase_of_not_mem]
+  simp_all
+
+theorem Nodup.erase_eq_filter [LawfulBEq α] {l} (d : Nodup l) (a : α) : l.erase a = l.filter (· != a) := by
+  induction d with
+  | nil => rfl
+  | cons m _n ih =>
+    rename_i b l
+    by_cases h : b = a
+    · subst h
+      rw [erase_cons_head, filter_cons_of_neg (by simp)]
+      apply Eq.symm
+      rw [filter_eq_self]
+      simpa [@eq_comm α] using m
+    · simp [beq_false_of_ne h, ih, h]
+
+theorem Nodup.mem_erase_iff [LawfulBEq α] {a : α} (d : Nodup l) : a ∈ l.erase b ↔ a ≠ b ∧ a ∈ l := by
+  rw [Nodup.erase_eq_filter d, mem_filter, and_comm, bne_iff_ne]
+
+theorem Nodup.not_mem_erase [LawfulBEq α] {a : α} (h : Nodup l) : a ∉ l.erase a := fun H => by
+  simpa using ((Nodup.mem_erase_iff h).mp H).left
+
+theorem Nodup.erase [LawfulBEq α] (a : α) : Nodup l → Nodup (l.erase a) :=
+  Nodup.sublist <| erase_sublist _ _
+
+end erase
+
+/-! ### eraseIdx -/
+
+theorem length_eraseIdx : ∀ {l i}, i < length l → length (@eraseIdx α l i) = length l - 1
+  | [], _, _ => rfl
+  | _::_, 0, _ => by simp [eraseIdx]
+  | x::xs, i+1, h => by
+    have : i < length xs := Nat.lt_of_succ_lt_succ h
+    simp [eraseIdx, ← Nat.add_one]
+    rw [length_eraseIdx this, Nat.sub_add_cancel (Nat.lt_of_le_of_lt (Nat.zero_le _) this)]
+
+@[simp] theorem eraseIdx_zero (l : List α) : eraseIdx l 0 = tail l := by cases l <;> rfl
+
+theorem eraseIdx_eq_take_drop_succ :
+    ∀ (l : List α) (i : Nat), l.eraseIdx i = l.take i ++ l.drop (i + 1)
+  | nil, _ => by simp
+  | a::l, 0 => by simp
+  | a::l, i + 1 => by simp [eraseIdx_eq_take_drop_succ l i]
+
+theorem eraseIdx_sublist : ∀ (l : List α) (k : Nat), eraseIdx l k <+ l
+  | [], _ => by simp
+  | a::l, 0 => by simp
+  | a::l, k + 1 => by simp [eraseIdx_sublist l k]
+
+theorem eraseIdx_subset (l : List α) (k : Nat) : eraseIdx l k ⊆ l := (eraseIdx_sublist l k).subset
+
+@[simp]
+theorem eraseIdx_eq_self : ∀ {l : List α} {k : Nat}, eraseIdx l k = l ↔ length l ≤ k
+  | [], _ => by simp
+  | a::l, 0 => by simp [(cons_ne_self _ _).symm]
+  | a::l, k + 1 => by simp [eraseIdx_eq_self]
+
+theorem eraseIdx_of_length_le {l : List α} {k : Nat} (h : length l ≤ k) : eraseIdx l k = l := by
+  rw [eraseIdx_eq_self.2 h]
+
+theorem eraseIdx_append_of_lt_length {l : List α} {k : Nat} (hk : k < length l) (l' : List α) :
+    eraseIdx (l ++ l') k = eraseIdx l k ++ l' := by
+  induction l generalizing k with
+  | nil => simp_all
+  | cons x l ih =>
+    cases k with
+    | zero => rfl
+    | succ k => simp_all [eraseIdx_cons_succ, Nat.succ_lt_succ_iff]
+
+theorem eraseIdx_append_of_length_le {l : List α} {k : Nat} (hk : length l ≤ k) (l' : List α) :
+    eraseIdx (l ++ l') k = l ++ eraseIdx l' (k - length l) := by
+  induction l generalizing k with
+  | nil => simp_all
+  | cons x l ih =>
+    cases k with
+    | zero => simp_all
+    | succ k => simp_all [eraseIdx_cons_succ, Nat.succ_sub_succ]
+
+protected theorem IsPrefix.eraseIdx {l l' : List α} (h : l <+: l') (k : Nat) :
+    eraseIdx l k <+: eraseIdx l' k := by
+  rcases h with ⟨t, rfl⟩
+  if hkl : k < length l then
+    simp [eraseIdx_append_of_lt_length hkl]
+  else
+    rw [Nat.not_lt] at hkl
+    simp [eraseIdx_append_of_length_le hkl, eraseIdx_of_length_le hkl]
+
+-- See also `mem_eraseIdx_iff_getElem` and `mem_eraseIdx_iff_getElem?` in
+-- `Init/Data/List/Nat/Basic.lean`.
+
+end List

src/Init/Data/List/Find.lean

@@ -0,0 +1,558 @@
+/-
+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,
+  Kim Morrison, Jannis Limperg
+-/
+prelude
+import Init.Data.List.Lemmas
+import Init.Data.List.Sublist
+import Init.Data.List.Range
+
+/-!
+# Lemmas about `List.find?`, `List.findSome?`, `List.findIdx`, `List.findIdx?`, and `List.indexOf`.
+-/
+
+namespace List
+
+open Nat
+
+/-! ### find? -/
+
+@[simp] theorem find?_cons_of_pos (l) (h : p a) : find? p (a :: l) = some a := by
+  simp [find?, h]
+
+@[simp] theorem find?_cons_of_neg (l) (h : ¬p a) : find? p (a :: l) = find? p l := by
+  simp [find?, h]
+
+@[simp] theorem find?_eq_none : find? p l = none ↔ ∀ x ∈ l, ¬ p x := by
+  induction l <;> simp [find?_cons]; split <;> simp [*]
+
+theorem find?_some : ∀ {l}, find? p l = some a → p a
+  | b :: l, H => by
+    by_cases h : p b <;> simp [find?, h] at H
+    · exact H ▸ h
+    · exact find?_some H
+
+@[simp] theorem mem_of_find?_eq_some : ∀ {l}, find? p l = some a → a ∈ l
+  | b :: l, H => by
+    by_cases h : p b <;> simp [find?, h] at H
+    · exact H ▸ .head _
+    · exact .tail _ (mem_of_find?_eq_some H)
+
+@[simp] theorem find?_map (f : β → α) (l : List β) : find? p (l.map f) = (l.find? (p ∘ f)).map f := by
+  induction l with
+  | nil => simp
+  | cons x xs ih =>
+    simp only [map_cons, find?]
+    by_cases h : p (f x) <;> simp [h, ih]
+
+theorem find?_append {l₁ l₂ : List α} : (l₁ ++ l₂).find? p = (l₁.find? p).or (l₂.find? p) := by
+  induction l₁ with
+  | nil => simp
+  | cons x xs ih =>
+    simp only [cons_append, find?]
+    by_cases h : p x <;> simp [h, ih]
+
+theorem find?_replicate : find? p (replicate n a) = if n = 0 then none else if p a then some a else none := by
+  cases n
+  · simp
+  · by_cases p a <;> simp_all [replicate_succ]
+
+@[simp] theorem find?_replicate_of_length_pos (h : 0 < n) : find? p (replicate n a) = if p a then some a else none := by
+  simp [find?_replicate, Nat.ne_of_gt h]
+
+@[simp] theorem find?_replicate_of_pos (h : p a) : find? p (replicate n a) = if n = 0 then none else some a := by
+  simp [find?_replicate, h]
+
+@[simp] theorem find?_replicate_of_neg (h : ¬ p a) : find? p (replicate n a) = none := by
+  simp [find?_replicate, h]
+
+theorem Sublist.find?_isSome {l₁ l₂ : List α} (h : l₁ <+ l₂) : (l₁.find? p).isSome → (l₂.find? p).isSome := by
+  induction h with
+  | slnil => simp
+  | cons a h ih
+  | cons₂ a h ih =>
+    simp only [find?]
+    split <;> simp_all
+
+theorem Sublist.find?_eq_none {l₁ l₂ : List α} (h : l₁ <+ l₂) : l₂.find? p = none → l₁.find? p = none := by
+  simp only [List.find?_eq_none, Bool.not_eq_true]
+  exact fun w x m => w x (Sublist.mem m h)
+
+theorem IsPrefix.find?_eq_some {l₁ l₂ : List α} {p : α → Bool} (h : l₁ <+: l₂) :
+    List.find? p l₁ = some b → List.find? p l₂ = some b := by
+  rw [IsPrefix] at h
+  obtain ⟨t, rfl⟩ := h
+  simp (config := {contextual := true}) [find?_append]
+
+theorem IsPrefix.find?_eq_none {l₁ l₂ : List α} {p : α → Bool} (h : l₁ <+: l₂) :
+    List.find? p l₂ = none → List.find? p l₁ = none :=
+  h.sublist.find?_eq_none
+theorem IsSuffix.find?_eq_none {l₁ l₂ : List α} {p : α → Bool} (h : l₁ <:+ l₂) :
+    List.find? p l₂ = none → List.find? p l₁ = none :=
+  h.sublist.find?_eq_none
+theorem IsInfix.find?_eq_none {l₁ l₂ : List α} {p : α → Bool} (h : l₁ <:+: l₂) :
+    List.find? p l₂ = none → List.find? p l₁ = none :=
+  h.sublist.find?_eq_none
+
+/-! ### findSome? -/
+
+@[simp] theorem findSome?_cons_of_isSome (l) (h : (f a).isSome) : findSome? f (a :: l) = f a := by
+  simp only [findSome?]
+  split <;> simp_all
+
+@[simp] theorem findSome?_cons_of_isNone (l) (h : (f a).isNone) : findSome? f (a :: l) = findSome? f l := by
+  simp only [findSome?]
+  split <;> simp_all
+
+theorem exists_of_findSome?_eq_some {l : List α} {f : α → Option β} (w : l.findSome? f = some b) :
+    ∃ a, a ∈ l ∧ f a = b := by
+  induction l with
+  | nil => simp_all
+  | cons h l ih =>
+    simp_all only [findSome?_cons, mem_cons, exists_eq_or_imp]
+    split at w <;> simp_all
+
+@[simp] theorem findSome?_eq_none : findSome? p l = none ↔ ∀ x ∈ l, p x = none := by
+  induction l <;> simp [findSome?_cons]; split <;> simp [*]
+
+@[simp] theorem map_findSome? (f : α → Option β) (g : β → γ) (l : List α) :
+    (l.findSome? f).map g = l.findSome? (Option.map g ∘ f) := by
+  induction l <;> simp [findSome?_cons]; split <;> simp [*]
+
+@[simp] theorem findSome?_map (f : β → γ) (l : List β) : findSome? p (l.map f) = l.findSome? (p ∘ f) := by
+  induction l with
+  | nil => simp
+  | cons x xs ih =>
+    simp only [map_cons, findSome?]
+    split <;> simp_all
+
+theorem findSome?_append {l₁ l₂ : List α} : (l₁ ++ l₂).findSome? f = (l₁.findSome? f).or (l₂.findSome? f) := by
+  induction l₁ with
+  | nil => simp
+  | cons x xs ih =>
+    simp only [cons_append, findSome?]
+    split <;> simp_all
+
+theorem findSome?_replicate : findSome? f (replicate n a) = if n = 0 then none else f a := by
+  cases n with
+  | zero => simp
+  | succ n =>
+    simp only [replicate_succ, findSome?_cons]
+    split <;> simp_all
+
+@[simp] theorem findSome?_replicate_of_pos (h : 0 < n) : findSome? f (replicate n a) = f a := by
+  simp [findSome?_replicate, Nat.ne_of_gt h]
+
+-- Argument is unused, but used to decide whether `simp` should unfold.
+@[simp] theorem find?_replicate_of_isSome (_ : (f a).isSome) : findSome? f (replicate n a) = if n = 0 then none else f a := by
+  simp [findSome?_replicate]
+
+@[simp] theorem find?_replicate_of_isNone (h : (f a).isNone) : findSome? f (replicate n a) = none := by
+  rw [Option.isNone_iff_eq_none] at h
+  simp [findSome?_replicate, h]
+
+theorem Sublist.findSome?_isSome {l₁ l₂ : List α} (h : l₁ <+ l₂) :
+    (l₁.findSome? f).isSome → (l₂.findSome? f).isSome := by
+  induction h with
+  | slnil => simp
+  | cons a h ih
+  | cons₂ a h ih =>
+    simp only [findSome?]
+    split <;> simp_all
+
+theorem Sublist.findSome?_eq_none {l₁ l₂ : List α} (h : l₁ <+ l₂) :
+    l₂.findSome? f = none → l₁.findSome? f = none := by
+  simp only [List.findSome?_eq_none, Bool.not_eq_true]
+  exact fun w x m => w x (Sublist.mem m h)
+
+theorem IsPrefix.findSome?_eq_some {l₁ l₂ : List α} {f : α → Option β} (h : l₁ <+: l₂) :
+    List.findSome? f l₁ = some b → List.findSome? f l₂ = some b := by
+  rw [IsPrefix] at h
+  obtain ⟨t, rfl⟩ := h
+  simp (config := {contextual := true}) [findSome?_append]
+
+theorem IsPrefix.findSome?_eq_none {l₁ l₂ : List α} {f : α → Option β} (h : l₁ <+: l₂) :
+    List.findSome? f l₂ = none → List.findSome? f l₁ = none :=
+  h.sublist.findSome?_eq_none
+theorem IsSuffix.findSome?_eq_none {l₁ l₂ : List α} {f : α → Option β} (h : l₁ <:+ l₂) :
+    List.findSome? f l₂ = none → List.findSome? f l₁ = none :=
+  h.sublist.findSome?_eq_none
+theorem IsInfix.findSome?_eq_none {l₁ l₂ : List α} {f : α → Option β} (h : l₁ <:+: l₂) :
+    List.findSome? f l₂ = none → List.findSome? f l₁ = none :=
+  h.sublist.findSome?_eq_none
+
+/-! ### findIdx -/
+
+theorem findIdx_cons (p : α → Bool) (b : α) (l : List α) :
+    (b :: l).findIdx p = bif p b then 0 else (l.findIdx p) + 1 := by
+  cases H : p b with
+  | true => simp [H, findIdx, findIdx.go]
+  | false => simp [H, findIdx, findIdx.go, findIdx_go_succ]
+where
+  findIdx_go_succ (p : α → Bool) (l : List α) (n : Nat) :
+      List.findIdx.go p l (n + 1) = (findIdx.go p l n) + 1 := by
+    cases l with
+    | nil => unfold findIdx.go; exact Nat.succ_eq_add_one n
+    | cons head tail =>
+      unfold findIdx.go
+      cases p head <;> simp only [cond_false, cond_true]
+      exact findIdx_go_succ p tail (n + 1)
+
+theorem findIdx_of_getElem?_eq_some {xs : List α} (w : xs[xs.findIdx p]? = some y) : p y := by
+  induction xs with
+  | nil => simp_all
+  | cons x xs ih => by_cases h : p x <;> simp_all [findIdx_cons]
+
+theorem findIdx_getElem {xs : List α} {w : xs.findIdx p < xs.length} :
+    p xs[xs.findIdx p] :=
+  xs.findIdx_of_getElem?_eq_some (getElem?_eq_getElem w)
+
+@[deprecated findIdx_of_getElem?_eq_some (since := "2024-08-12")]
+theorem findIdx_of_get?_eq_some {xs : List α} (w : xs.get? (xs.findIdx p) = some y) : p y :=
+  findIdx_of_getElem?_eq_some (by simpa using w)
+
+@[deprecated findIdx_getElem (since := "2024-08-12")]
+theorem findIdx_get {xs : List α} {w : xs.findIdx p < xs.length} :
+    p (xs.get ⟨xs.findIdx p, w⟩) :=
+  xs.findIdx_of_getElem?_eq_some (getElem?_eq_getElem w)
+
+theorem findIdx_lt_length_of_exists {xs : List α} (h : ∃ x ∈ xs, p x) :
+    xs.findIdx p < xs.length := by
+  induction xs with
+  | nil => simp_all
+  | cons x xs ih =>
+    by_cases p x
+    · simp_all only [forall_exists_index, and_imp, mem_cons, exists_eq_or_imp, true_or,
+        findIdx_cons, cond_true, length_cons]
+      apply Nat.succ_pos
+    · simp_all [findIdx_cons, Nat.succ_lt_succ_iff]
+      obtain ⟨x', m', h'⟩ := h
+      exact ih x' m' h'
+
+theorem findIdx_getElem?_eq_getElem_of_exists {xs : List α} (h : ∃ x ∈ xs, p x) :
+    xs[xs.findIdx p]? = some (xs[xs.findIdx p]'(xs.findIdx_lt_length_of_exists h)) :=
+  getElem?_eq_getElem (findIdx_lt_length_of_exists h)
+
+@[deprecated findIdx_getElem?_eq_getElem_of_exists (since := "2024-08-12")]
+theorem findIdx_get?_eq_get_of_exists {xs : List α} (h : ∃ x ∈ xs, p x) :
+    xs.get? (xs.findIdx p) = some (xs.get ⟨xs.findIdx p, xs.findIdx_lt_length_of_exists h⟩) :=
+  get?_eq_get (findIdx_lt_length_of_exists h)
+
+@[simp]
+theorem findIdx_eq_length {p : α → Bool} {xs : List α} :
+    xs.findIdx p = xs.length ↔ ∀ x ∈ xs, p x = false := by
+  induction xs with
+  | nil => simp_all
+  | cons x xs ih =>
+    rw [findIdx_cons, length_cons]
+    simp only [cond_eq_if]
+    split <;> simp_all [Nat.succ.injEq]
+
+theorem findIdx_eq_length_of_false {p : α → Bool} {xs : List α} (h : ∀ x ∈ xs, p x = false) :
+    xs.findIdx p = xs.length := by
+  rw [findIdx_eq_length]
+  exact h
+
+theorem findIdx_le_length (p : α → Bool) {xs : List α} : xs.findIdx p ≤ xs.length := by
+  by_cases e : ∃ x ∈ xs, p x
+  · exact Nat.le_of_lt (findIdx_lt_length_of_exists e)
+  · simp at e
+    exact Nat.le_of_eq (findIdx_eq_length.mpr e)
+
+@[simp]
+theorem findIdx_lt_length {p : α → Bool} {xs : List α} :
+    xs.findIdx p < xs.length ↔ ∃ x ∈ xs, p x := by
+  rw [← Decidable.not_iff_not, Nat.not_lt]
+  have := @Nat.le_antisymm_iff (xs.findIdx p) xs.length
+  simp only [findIdx_le_length, true_and] at this
+  rw [← this, findIdx_eq_length, not_exists]
+  simp only [Bool.not_eq_true, not_and]
+
+/-- `p` does not hold for elements with indices less than `xs.findIdx p`. -/
+theorem not_of_lt_findIdx {p : α → Bool} {xs : List α} {i : Nat} (h : i < xs.findIdx p) :
+    ¬p (xs[i]'(Nat.le_trans h (findIdx_le_length p))) := by
+  revert i
+  induction xs with
+  | nil => intro i h; rw [findIdx_nil] at h; simp at h
+  | cons x xs ih =>
+    intro i h
+    have ho := h
+    rw [findIdx_cons] at h
+    have npx : ¬p x := by intro y; rw [y, cond_true] at h; simp at h
+    simp [npx, cond_false] at h
+    cases i.eq_zero_or_pos with
+    | inl e => simpa only [e, Fin.zero_eta, get_cons_zero]
+    | inr e =>
+      have ipm := Nat.succ_pred_eq_of_pos e
+      have ilt := Nat.le_trans ho (findIdx_le_length p)
+      simp (config := { singlePass := true }) only [← ipm, getElem_cons_succ]
+      rw [← ipm, Nat.succ_lt_succ_iff] at h
+      simpa using ih h
+
+/-- If `¬ p xs[j]` for all `j < i`, then `i ≤ xs.findIdx p`. -/
+theorem le_findIdx_of_not {p : α → Bool} {xs : List α} {i : Nat} (h : i < xs.length)
+    (h2 : ∀ j (hji : j < i), ¬p (xs[j]'(Nat.lt_trans hji h))) : i ≤ xs.findIdx p := by
+  apply Decidable.byContradiction
+  intro f
+  simp only [Nat.not_le] at f
+  exact absurd (@findIdx_getElem _ p xs (Nat.lt_trans f h)) (h2 (xs.findIdx p) f)
+
+/-- If `¬ p xs[j]` for all `j ≤ i`, then `i < xs.findIdx p`. -/
+theorem lt_findIdx_of_not {p : α → Bool} {xs : List α} {i : Nat} (h : i < xs.length)
+    (h2 : ∀ j (hji : j ≤ i), ¬p (xs.get ⟨j, Nat.lt_of_le_of_lt hji h⟩)) : i < xs.findIdx p := by
+  apply Decidable.byContradiction
+  intro f
+  simp only [Nat.not_lt] at f
+  exact absurd (@findIdx_getElem _ p xs (Nat.lt_of_le_of_lt f h)) (h2 (xs.findIdx p) f)
+
+/-- `xs.findIdx p = i` iff `p xs[i]` and `¬ p xs [j]` for all `j < i`. -/
+theorem findIdx_eq {p : α → Bool} {xs : List α} {i : Nat} (h : i < xs.length) :
+    xs.findIdx p = i ↔ p xs[i] ∧ ∀ j (hji : j < i), ¬p (xs[j]'(Nat.lt_trans hji h)) := by
+  refine ⟨fun f ↦ ⟨f ▸ (@findIdx_getElem _ p xs (f ▸ h)), fun _ hji ↦ not_of_lt_findIdx (f ▸ hji)⟩,
+    fun ⟨h1, h2⟩ ↦ ?_⟩
+  apply Nat.le_antisymm _ (le_findIdx_of_not h h2)
+  apply Decidable.byContradiction
+  intro h3
+  simp at h3
+  exact not_of_lt_findIdx h3 h1
+
+theorem findIdx_append (p : α → Bool) (l₁ l₂ : List α) :
+    (l₁ ++ l₂).findIdx p =
+      if l₁.findIdx p < l₁.length then l₁.findIdx p else l₂.findIdx p + l₁.length := by
+  simp
+  induction l₁ with
+  | nil => simp
+  | cons x xs ih =>
+    simp only [findIdx_cons, length_cons, cons_append]
+    by_cases h : p x
+    · simp [h]
+    · simp only [h, ih, cond_eq_if, Bool.false_eq_true, ↓reduceIte, mem_cons, exists_eq_or_imp,
+        false_or]
+      split <;> simp [Nat.add_assoc]
+
+theorem IsPrefix.findIdx_le {l₁ l₂ : List α} {p : α → Bool} (h : l₁ <+: l₂) :
+    l₁.findIdx p ≤ l₂.findIdx p := by
+  rw [IsPrefix] at h
+  obtain ⟨t, rfl⟩ := h
+  simp only [findIdx_append, findIdx_lt_length]
+  split
+  · exact Nat.le_refl ..
+  · simp_all [findIdx_eq_length_of_false]
+
+theorem IsPrefix.findIdx_eq_of_findIdx_lt_length {l₁ l₂ : List α} {p : α → Bool} (h : l₁ <+: l₂)
+    (lt : l₁.findIdx p < l₁.length) : l₂.findIdx p = l₁.findIdx p := by
+  rw [IsPrefix] at h
+  obtain ⟨t, rfl⟩ := h
+  simp only [findIdx_append, findIdx_lt_length]
+  split
+  · rfl
+  · simp_all
+
+/-! ### findIdx? -/
+
+@[simp] theorem findIdx?_nil : ([] : List α).findIdx? p i = none := rfl
+
+@[simp] theorem findIdx?_cons :
+    (x :: xs).findIdx? p i = if p x then some i else findIdx? p xs (i + 1) := rfl
+
+@[simp] theorem findIdx?_succ :
+    (xs : List α).findIdx? p (i+1) = (xs.findIdx? p i).map fun i => i + 1 := by
+  induction xs generalizing i with simp
+  | cons _ _ _ => split <;> simp_all
+
+@[simp]
+theorem findIdx?_eq_none_iff {xs : List α} {p : α → Bool} :
+    xs.findIdx? p = none ↔ ∀ x, x ∈ xs → p x = false := by
+  induction xs with
+  | nil => simp_all
+  | cons x xs ih =>
+    simp only [findIdx?_cons]
+    split <;> simp_all [cond_eq_if]
+
+theorem findIdx?_isSome {xs : List α} {p : α → Bool} :
+    (xs.findIdx? p).isSome = xs.any p := by
+  induction xs with
+  | nil => simp
+  | cons x xs ih =>
+    simp only [findIdx?_cons]
+    split <;> simp_all
+
+theorem findIdx?_isNone {xs : List α} {p : α → Bool} :
+    (xs.findIdx? p).isNone = xs.all (¬p ·) := by
+  induction xs with
+  | nil => simp
+  | cons x xs ih =>
+    simp only [findIdx?_cons]
+    split <;> simp_all
+
+theorem findIdx?_eq_some_iff_findIdx_eq {xs : List α} {p : α → Bool} {i : Nat} :
+    xs.findIdx? p = some i ↔ i < xs.length ∧ xs.findIdx p = i := by
+  induction xs generalizing i with
+  | nil => simp_all
+  | cons x xs ih =>
+    simp only [findIdx?_cons, findIdx_cons]
+    split
+    · simp_all [cond_eq_if]
+      rintro rfl
+      exact zero_lt_succ xs.length
+    · simp_all [cond_eq_if, and_assoc]
+      constructor
+      · rintro ⟨a, lt, rfl, rfl⟩
+        simp_all [Nat.succ_lt_succ_iff]
+      · rintro ⟨h, rfl⟩
+        exact ⟨_, by simp_all [Nat.succ_lt_succ_iff], rfl, rfl⟩
+
+theorem findIdx?_eq_some_of_exists {xs : List α} {p : α → Bool} (h : ∃ x, x ∈ xs ∧ p x) :
+    xs.findIdx? p = some (xs.findIdx p) := by
+  rw [findIdx?_eq_some_iff_findIdx_eq]
+  exact ⟨findIdx_lt_length_of_exists h, rfl⟩
+
+theorem findIdx?_eq_none_iff_findIdx_eq {xs : List α} {p : α → Bool} :
+    xs.findIdx? p = none ↔ xs.findIdx p = xs.length := by
+  simp
+
+theorem findIdx?_eq_some_iff_getElem (xs : List α) (p : α → Bool) :
+    xs.findIdx? p = some i ↔
+      ∃ h : i < xs.length, p xs[i] ∧ ∀ j (hji : j < i), ¬p (xs[j]'(Nat.lt_trans hji h)) := by
+  induction xs generalizing i with
+  | nil => simp
+  | cons x xs ih =>
+    simp only [findIdx?_cons, Nat.zero_add, findIdx?_succ]
+    split
+    · simp only [Option.some.injEq, Bool.not_eq_true, length_cons]
+      cases i with
+      | zero => simp_all
+      | succ i =>
+        simp only [Bool.not_eq_true, zero_ne_add_one, getElem_cons_succ, false_iff, not_exists,
+          not_and, Classical.not_forall, Bool.not_eq_false]
+        intros
+        refine ⟨0, zero_lt_succ i, ‹_›⟩
+    · simp only [Option.map_eq_some', ih, Bool.not_eq_true, length_cons]
+      constructor
+      · rintro ⟨a, ⟨⟨h, h₁, h₂⟩, rfl⟩⟩
+        refine ⟨Nat.succ_lt_succ_iff.mpr h, by simpa, fun j hj => ?_⟩
+        cases j with
+        | zero => simp_all
+        | succ j =>
+          apply h₂
+          simp_all [Nat.succ_lt_succ_iff]
+      · rintro ⟨h, h₁, h₂⟩
+        cases i with
+        | zero => simp_all
+        | succ i =>
+          refine ⟨i, ⟨Nat.succ_lt_succ_iff.mp h, by simpa, fun j hj => ?_⟩, rfl⟩
+          simpa using h₂ (j + 1) (Nat.succ_lt_succ_iff.mpr hj)
+
+theorem findIdx?_of_eq_some {xs : List α} {p : α → Bool} (w : xs.findIdx? p = some i) :
+    match xs[i]? with | some a => p a | none => false := by
+  induction xs generalizing i with
+  | nil => simp_all
+  | cons x xs ih =>
+    simp_all only [findIdx?_cons, Nat.zero_add, findIdx?_succ]
+    split at w <;> cases i <;> simp_all [succ_inj']
+
+theorem findIdx?_of_eq_none {xs : List α} {p : α → Bool} (w : xs.findIdx? p = none) :
+    ∀ i : Nat, match xs[i]? with | some a => ¬ p a | none => true := by
+  intro i
+  induction xs generalizing i with
+  | nil => simp_all
+  | cons x xs ih =>
+    simp_all only [Bool.not_eq_true, findIdx?_cons, Nat.zero_add, findIdx?_succ]
+    cases i with
+    | zero =>
+      split at w <;> simp_all
+    | succ i =>
+      simp only [getElem?_cons_succ]
+      apply ih
+      split at w <;> simp_all
+
+@[simp] theorem findIdx?_map (f : β → α) (l : List β) : findIdx? p (l.map f) = l.findIdx? (p ∘ f) := by
+  induction l with
+  | nil => simp
+  | cons x xs ih =>
+    simp only [map_cons, findIdx?]
+    split <;> simp_all
+
+@[simp] theorem findIdx?_append :
+    (xs ++ ys : List α).findIdx? p =
+      (xs.findIdx? p).or ((ys.findIdx? p).map fun i => i + xs.length) := by
+  induction xs with simp
+  | cons _ _ _ => split <;> simp_all [Option.map_or', Option.map_map]; rfl
+
+theorem findIdx?_join {l : List (List α)} {p : α → Bool} :
+    l.join.findIdx? p =
+      (l.findIdx? (·.any p)).map
+        fun i => Nat.sum ((l.take i).map List.length) +
+          (l[i]?.map fun xs => xs.findIdx p).getD 0 := by
+  induction l with
+  | nil => simp
+  | cons xs l ih =>
+    simp only [join, findIdx?_append, map_take, map_cons, findIdx?, any_eq_true, Nat.zero_add,
+      findIdx?_succ]
+    split
+    · simp only [Option.map_some', take_zero, sum_nil, length_cons, zero_lt_succ,
+        getElem?_eq_getElem, getElem_cons_zero, Option.getD_some, Nat.zero_add]
+      rw [Option.or_of_isSome (by simpa [findIdx?_isSome])]
+      rw [findIdx?_eq_some_of_exists ‹_›]
+    · simp_all only [map_take, not_exists, not_and, Bool.not_eq_true, Option.map_map]
+      rw [Option.or_of_isNone (by simpa [findIdx?_isNone])]
+      congr 1
+      ext i
+      simp [Nat.add_comm, Nat.add_assoc]
+
+@[simp] theorem findIdx?_replicate :
+    (replicate n a).findIdx? p = if 0 < n ∧ p a then some 0 else none := by
+  cases n with
+  | zero => simp
+  | succ n =>
+    simp only [replicate, findIdx?_cons, Nat.zero_add, findIdx?_succ, zero_lt_succ, true_and]
+    split <;> simp_all
+
+theorem findIdx?_eq_enum_findSome? {xs : List α} {p : α → Bool} :
+    xs.findIdx? p = xs.enum.findSome? fun ⟨i, a⟩ => if p a then some i else none := by
+  induction xs with
+  | nil => simp
+  | cons x xs ih =>
+    simp only [findIdx?_cons, Nat.zero_add, findIdx?_succ, enum]
+    split
+    · simp_all
+    · simp_all only [enumFrom_cons, ite_false, Option.isNone_none, findSome?_cons_of_isNone]
+      simp [Function.comp_def, ← map_fst_add_enum_eq_enumFrom]
+
+theorem Sublist.findIdx?_isSome {l₁ l₂ : List α} (h : l₁ <+ l₂) :
+    (l₁.findIdx? p).isSome → (l₂.findIdx? p).isSome := by
+  simp only [List.findIdx?_isSome, any_eq_true]
+  rintro ⟨w, m, q⟩
+  exact ⟨w, h.mem m, q⟩
+
+theorem Sublist.findIdx?_eq_none {l₁ l₂ : List α} (h : l₁ <+ l₂) :
+    l₂.findIdx? p = none → l₁.findIdx? p = none := by
+  simp only [findIdx?_eq_none_iff]
+  exact fun w x m => w x (h.mem m)
+
+theorem IsPrefix.findIdx?_eq_some {l₁ l₂ : List α} {p : α → Bool} (h : l₁ <+: l₂) :
+    List.findIdx? p l₁ = some i → List.findIdx? p l₂ = some i := by
+  rw [IsPrefix] at h
+  obtain ⟨t, rfl⟩ := h
+  intro h
+  simp [findIdx?_append, h]
+theorem IsPrefix.findIdx?_eq_none {l₁ l₂ : List α} {p : α → Bool} (h : l₁ <+: l₂) :
+    List.findIdx? p l₂ = none → List.findIdx? p l₁ = none :=
+  h.sublist.findIdx?_eq_none
+theorem IsSuffix.findIdx?_eq_none {l₁ l₂ : List α} {p : α → Bool} (h : l₁ <:+ l₂) :
+    List.findIdx? p l₂ = none → List.findIdx? p l₁ = none :=
+  h.sublist.findIdx?_eq_none
+theorem IsInfix.findIdx?_eq_none {l₁ l₂ : List α} {p : α → Bool} (h : l₁ <:+: l₂) :
+    List.findIdx? p l₂ = none → List.findIdx? p l₁ = none :=
+  h.sublist.findIdx?_eq_none
+
+/-! ### indexOf -/
+
+theorem indexOf_cons [BEq α] :
+    (x :: xs : List α).indexOf y = bif x == y then 0 else xs.indexOf y + 1 := by
+  dsimp [indexOf]
+  simp [findIdx_cons]
+
+end List

src/Init/Data/List/Impl.lean

@@ -193,6 +193,17 @@ theorem replicateTR_loop_eq : ∀ n, replicateTR.loop a n acc = replicate n a ++
   apply funext; intro α; apply funext; intro n; apply funext; intro a
   exact (replicateTR_loop_replicate_eq _ 0 n).symm
 
+/-! ## Additional functions -/
+
+/-! ### leftpad -/
+
+/-- Optimized version of `leftpad`. -/
+@[inline] def leftpadTR (n : Nat) (a : α) (l : List α) : List α :=
+  replicateTR.loop a (n - length l) l
+
+@[csimp] theorem leftpad_eq_leftpadTR : @leftpad = @leftpadTR := by
+  funext α n a l; simp [leftpad, leftpadTR, replicateTR_loop_eq]
+
 /-! ## Sublists -/
 
 /-! ### take -/
@@ -366,6 +377,26 @@ def unzipTR (l : List (α × β)) : List α × List β :=
 
 /-! ## Ranges and enumeration -/
 
+/-! ### range' -/
+
+/-- Optimized version of `range'`. -/
+@[inline] def range'TR (s n : Nat) (step : Nat := 1) : List Nat := go n (s + step * n) [] where
+  /-- Auxiliary for `range'TR`: `range'TR.go n e = [e-n, ..., e-1] ++ acc`. -/
+  go : Nat → Nat → List Nat → List Nat
+  | 0, _, acc => acc
+  | n+1, e, acc => go n (e-step) ((e-step) :: acc)
+
+@[csimp] theorem range'_eq_range'TR : @range' = @range'TR := by
+  funext s n step
+  let rec go (s) : ∀ n m,
+    range'TR.go step n (s + step * n) (range' (s + step * n) m step) = range' s (n + m) step
+  | 0, m => by simp [range'TR.go]
+  | n+1, m => by
+    simp [range'TR.go]
+    rw [Nat.mul_succ, ← Nat.add_assoc, Nat.add_sub_cancel, Nat.add_right_comm n]
+    exact go s n (m + 1)
+  exact (go s n 0).symm
+
 /-! ### iota -/
 
 /-- Tail-recursive version of `List.iota`. -/

src/Init/Data/List/MinMax.lean

@@ -0,0 +1,153 @@
+/-
+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.Lemmas
+
+/-!
+# Lemmas about `List.minimum?` and `List.maximum?.
+-/
+
+namespace List
+
+open Nat
+
+/-! ## Minima and maxima -/
+
+/-! ### 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]
+
+-- See also `Init.Data.List.Nat.Basic` for specialisations of the next two results to `Nat`.
+
+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))
+
+theorem minimum?_replicate [Min α] {n : Nat} {a : α} (w : min a a = a) :
+    (replicate n a).minimum? = if n = 0 then none else some a := by
+  induction n with
+  | zero => rfl
+  | succ n ih => cases n <;> simp_all [replicate_succ, minimum?_cons]
+
+@[simp] theorem minimum?_replicate_of_pos [Min α] {n : Nat} {a : α} (w : min a a = a) (h : 0 < n) :
+    (replicate n a).minimum? = some a := by
+  simp [minimum?_replicate, Nat.ne_of_gt h, w]
+
+/-! ### maximum? -/
+
+@[simp] theorem maximum?_nil [Max α] : ([] : List α).maximum? = none := rfl
+
+-- We don't put `@[simp]` on `maximum?_cons`,
+-- because the definition in terms of `foldl` is not useful for proofs.
+theorem maximum?_cons [Max α] {xs : List α} : (x :: xs).maximum? = foldl max x xs := rfl
+
+@[simp] theorem maximum?_eq_none_iff {xs : List α} [Max α] : xs.maximum? = none ↔ xs = [] := by
+  cases xs <;> simp [maximum?]
+
+theorem maximum?_mem [Max α] (min_eq_or : ∀ a b : α, max a b = a ∨ max a b = b) :
+    {xs : List α} → xs.maximum? = some a → a ∈ xs
+  | nil => by simp
+  | cons x xs => by
+    rw [maximum?]; rintro ⟨⟩
+    induction xs generalizing x with simp at *
+    | cons y xs ih =>
+      rcases ih (max x y) with h | h <;> simp [h]
+      simp [← or_assoc, min_eq_or x y]
+
+-- See also `Init.Data.List.Nat.Basic` for specialisations of the next two results to `Nat`.
+
+theorem maximum?_le_iff [Max α] [LE α]
+    (max_le_iff : ∀ a b c : α, max b c ≤ a ↔ b ≤ a ∧ c ≤ a) :
+    {xs : List α} → xs.maximum? = some a → ∀ x, a ≤ x ↔ ∀ b ∈ xs, b ≤ x
+  | nil => by simp
+  | cons x xs => by
+    rw [maximum?]; rintro ⟨⟩ y
+    induction xs generalizing x with
+    | nil => simp
+    | cons y xs ih => simp [ih, max_le_iff, and_assoc]
+
+-- This could be refactored by designing appropriate typeclasses to replace `le_refl`, `max_eq_or`,
+-- and `le_min_iff`.
+theorem maximum?_eq_some_iff [Max α] [LE α] [anti : Antisymm ((· : α) ≤ ·)]
+    (le_refl : ∀ a : α, a ≤ a)
+    (max_eq_or : ∀ a b : α, max a b = a ∨ max a b = b)
+    (max_le_iff : ∀ a b c : α, max b c ≤ a ↔ b ≤ a ∧ c ≤ a) {xs : List α} :
+    xs.maximum? = some a ↔ a ∈ xs ∧ ∀ b ∈ xs, b ≤ a := by
+  refine ⟨fun h => ⟨maximum?_mem max_eq_or h, (maximum?_le_iff max_le_iff h _).1 (le_refl _)⟩, ?_⟩
+  intro ⟨h₁, h₂⟩
+  cases xs with
+  | nil => simp at h₁
+  | cons x xs =>
+    exact congrArg some <| anti.1
+      (h₂ _ (maximum?_mem max_eq_or (xs := x::xs) rfl))
+      ((maximum?_le_iff max_le_iff (xs := x::xs) rfl _).1 (le_refl _) _ h₁)
+
+theorem maximum?_replicate [Max α] {n : Nat} {a : α} (w : max a a = a) :
+    (replicate n a).maximum? = if n = 0 then none else some a := by
+  induction n with
+  | zero => rfl
+  | succ n ih => cases n <;> simp_all [replicate_succ, maximum?_cons]
+
+@[simp] theorem maximum?_replicate_of_pos [Max α] {n : Nat} {a : α} (w : max a a = a) (h : 0 < n) :
+    (replicate n a).maximum? = some a := by
+  simp [maximum?_replicate, Nat.ne_of_gt h, w]
+
+end List

src/Init/Data/List/Monadic.lean

@@ -0,0 +1,69 @@
+/-
+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.TakeDrop
+
+/-!
+# Lemmas about `List.mapM` and `List.forM`.
+-/
+
+namespace List
+
+open Nat
+
+/-! ## Monadic operations -/
+
+-- 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 `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.
+
+/-! ### 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`:
+
+@[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 _ _ _
+
+@[simp] theorem forM_append [Monad m] [LawfulMonad m] (l₁ l₂ : List α) (f : α → m PUnit) :
+    (l₁ ++ l₂).forM f = (do l₁.forM f; l₂.forM f) := by
+  induction l₁ <;> simp [*]
+
+end List

src/Init/Data/List/Nat.lean

@@ -0,0 +1,11 @@
+/-
+Copyright (c) 2024 Lean FRO. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Kim Morrison
+-/
+prelude
+import Init.Data.List.Nat.Basic
+import Init.Data.List.Nat.Pairwise
+import Init.Data.List.Nat.Range
+import Init.Data.List.Nat.Sublist
+import Init.Data.List.Nat.TakeDrop

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

@@ -0,0 +1,133 @@
+/-
+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.Count
+import Init.Data.List.MinMax
+import Init.Data.Nat.Lemmas
+
+/-!
+# Miscellaneous `List` lemmas, that require more `Nat` lemmas than are available in `Init.Data.List.Lemmas`.
+
+In particular, `omega` is available here.
+-/
+
+open Nat
+
+namespace List
+
+/-! ### filter -/
+
+theorem length_filter_lt_length_iff_exists (l) :
+    length (filter p l) < length l ↔ ∃ x ∈ l, ¬p x := by
+  simpa [length_eq_countP_add_countP p l, countP_eq_length_filter] using
+  countP_pos (fun x => ¬p x) (l := l)
+
+/-! ### reverse -/
+
+theorem getElem_eq_getElem_reverse {l : List α} {i} (h : i < l.length) :
+    l[i] = l.reverse[l.length - 1 - i]'(by simpa using Nat.sub_one_sub_lt_of_lt h) := by
+  rw [getElem_reverse]
+  congr
+  omega
+
+/-! ### leftpad -/
+
+/-- The length of the List returned by `List.leftpad n a l` is equal
+  to the larger of `n` and `l.length` -/
+@[simp]
+theorem leftpad_length (n : Nat) (a : α) (l : List α) :
+    (leftpad n a l).length = max n l.length := by
+  simp only [leftpad, length_append, length_replicate, Nat.sub_add_eq_max]
+
+/-! ### eraseIdx -/
+
+theorem mem_eraseIdx_iff_getElem {x : α} :
+    ∀ {l} {k}, x ∈ eraseIdx l k ↔ ∃ i h, i ≠ k ∧ l[i]'h = x
+  | [], _ => by
+    simp only [eraseIdx, not_mem_nil, false_iff]
+    rintro ⟨i, h, -⟩
+    exact Nat.not_lt_zero _ h
+  | a::l, 0 => by simp [mem_iff_getElem, Nat.succ_lt_succ_iff]
+  | a::l, k+1 => by
+    rw [← Nat.or_exists_add_one]
+    simp [mem_eraseIdx_iff_getElem, @eq_comm _ a, succ_inj', Nat.succ_lt_succ_iff]
+
+theorem mem_eraseIdx_iff_getElem? {x : α} {l} {k} : x ∈ eraseIdx l k ↔ ∃ i ≠ k, l[i]? = some x := by
+  simp only [mem_eraseIdx_iff_getElem, getElem_eq_iff, exists_and_left]
+  refine exists_congr fun i => and_congr_right' ?_
+  constructor
+  · rintro ⟨_, h⟩; exact h
+  · rintro h;
+    obtain ⟨h', -⟩ := getElem?_eq_some.1 h
+    exact ⟨h', h⟩
+
+/-! ### minimum? -/
+
+-- A specialization of `minimum?_eq_some_iff` to Nat.
+theorem minimum?_eq_some_iff' {xs : List Nat} :
+    xs.minimum? = some a ↔ (a ∈ xs ∧ ∀ b ∈ xs, a ≤ b) :=
+  minimum?_eq_some_iff
+    (le_refl := Nat.le_refl)
+    (min_eq_or := fun _ _ => by omega)
+    (le_min_iff := fun _ _ _ => by omega)
+
+-- This could be generalized,
+-- but will first require further work on order typeclasses in the core repository.
+theorem minimum?_cons' {a : Nat} {l : List Nat} :
+    (a :: l).minimum? = some (match l.minimum? with
+    | none => a
+    | some m => min a m) := by
+  rw [minimum?_eq_some_iff']
+  split <;> rename_i h m
+  · simp_all
+  · rw [minimum?_eq_some_iff'] at m
+    obtain ⟨m, le⟩ := m
+    rw [Nat.min_def]
+    constructor
+    · split
+      · exact mem_cons_self a l
+      · exact mem_cons_of_mem a m
+    · intro b m
+      cases List.mem_cons.1 m with
+      | inl => split <;> omega
+      | inr h =>
+        specialize le b h
+        split <;> omega
+
+/-! ### maximum? -/
+
+-- A specialization of `maximum?_eq_some_iff` to Nat.
+theorem maximum?_eq_some_iff' {xs : List Nat} :
+    xs.maximum? = some a ↔ (a ∈ xs ∧ ∀ b ∈ xs, b ≤ a) :=
+  maximum?_eq_some_iff
+    (le_refl := Nat.le_refl)
+    (max_eq_or := fun _ _ => by omega)
+    (max_le_iff := fun _ _ _ => by omega)
+
+-- This could be generalized,
+-- but will first require further work on order typeclasses in the core repository.
+theorem maximum?_cons' {a : Nat} {l : List Nat} :
+    (a :: l).maximum? = some (match l.maximum? with
+    | none => a
+    | some m => max a m) := by
+  rw [maximum?_eq_some_iff']
+  split <;> rename_i h m
+  · simp_all
+  · rw [maximum?_eq_some_iff'] at m
+    obtain ⟨m, le⟩ := m
+    rw [Nat.max_def]
+    constructor
+    · split
+      · exact mem_cons_of_mem a m
+      · exact mem_cons_self a l
+    · intro b m
+      cases List.mem_cons.1 m with
+      | inl => split <;> omega
+      | inr h =>
+        specialize le b h
+        split <;> omega
+
+end List

src/Init/Data/List/Nat/Pairwise.lean

@@ -0,0 +1,73 @@
+/-
+Copyright (c) 2018 Mario Carneiro. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Mario Carneiro, James Gallicchio
+-/
+prelude
+import Init.Data.Fin.Lemmas
+import Init.Data.List.Nat.TakeDrop
+import Init.Data.List.Pairwise
+
+/-!
+# Lemmas about `List.Pairwise`
+-/
+
+namespace List
+
+/-- Given a list `is` of monotonically increasing indices into `l`, getting each index
+  produces a sublist of `l`.  -/
+theorem map_getElem_sublist {l : List α} {is : List (Fin l.length)} (h : is.Pairwise (· < ·)) :
+    is.map (l[·]) <+ l := by
+  suffices ∀ n l', l' = l.drop n → (∀ i ∈ is, n ≤ i) → map (l[·]) is <+ l'
+    from this 0 l (by simp) (by simp)
+  rintro n l' rfl his
+  induction is generalizing n with
+  | nil => simp
+  | cons hd tl IH =>
+    simp only [Fin.getElem_fin, map_cons]
+    have := IH h.of_cons (hd+1) (pairwise_cons.mp h).1
+    specialize his hd (.head _)
+    have := (drop_eq_getElem_cons ..).symm ▸ this.cons₂ (get l hd)
+    have := Sublist.append (nil_sublist (take hd l |>.drop n)) this
+    rwa [nil_append, ← (drop_append_of_le_length ?_), take_append_drop] at this
+    simp [Nat.min_eq_left (Nat.le_of_lt hd.isLt), his]
+
+@[deprecated map_getElem_sublist (since := "2024-07-30")]
+theorem map_get_sublist {l : List α} {is : List (Fin l.length)} (h : is.Pairwise (·.val < ·.val)) :
+    is.map (get l) <+ l := by
+  simpa using map_getElem_sublist h
+
+/-- Given a sublist `l' <+ l`, there exists an increasing list of indices `is` such that
+  `l' = is.map fun i => l[i]`. -/
+theorem sublist_eq_map_getElem {l l' : List α} (h : l' <+ l) : ∃ is : List (Fin l.length),
+    l' = is.map (l[·]) ∧ is.Pairwise (· < ·) := by
+  induction h with
+  | slnil => exact ⟨[], by simp⟩
+  | cons _ _ IH =>
+    let ⟨is, IH⟩ := IH
+    refine ⟨is.map (·.succ), ?_⟩
+    simpa [Function.comp_def, pairwise_map]
+  | cons₂ _ _ IH =>
+    rcases IH with ⟨is,IH⟩
+    refine ⟨⟨0, by simp [Nat.zero_lt_succ]⟩ :: is.map (·.succ), ?_⟩
+    simp [Function.comp_def, pairwise_map, IH, ← get_eq_getElem]
+
+@[deprecated sublist_eq_map_getElem (since := "2024-07-30")]
+theorem sublist_eq_map_get (h : l' <+ l) : ∃ is : List (Fin l.length),
+    l' = map (get l) is ∧ is.Pairwise (· < ·) := by
+  simpa using sublist_eq_map_getElem h
+
+theorem pairwise_iff_getElem : Pairwise R l ↔
+    ∀ (i j : Nat) (_hi : i < l.length) (_hj : j < l.length) (_hij : i < j), R l[i] l[j] := by
+  rw [pairwise_iff_forall_sublist]
+  constructor <;> intro h
+  · intros i j hi hj h'
+    apply h
+    simpa [h'] using map_getElem_sublist (is := [⟨i, hi⟩, ⟨j, hj⟩])
+  · intros a b h'
+    have ⟨is, h', hij⟩ := sublist_eq_map_getElem h'
+    rcases is with ⟨⟩ | ⟨a', ⟨⟩ | ⟨b', ⟨⟩⟩⟩ <;> simp at h'
+    rcases h' with ⟨rfl, rfl⟩
+    apply h; simpa using hij
+
+end List

src/Init/Data/List/Nat/Range.lean

@@ -0,0 +1,378 @@
+/-
+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.Nat.TakeDrop
+import Init.Data.List.Range
+import Init.Data.List.Pairwise
+
+/-!
+# Lemmas about `List.range` and `List.enum`
+-/
+
+namespace List
+
+open Nat
+
+/-! ## Ranges and enumeration -/
+
+/-! ### range' -/
+
+theorem range'_succ (s n step) : range' s (n + 1) step = s :: range' (s + step) n step := by
+  simp [range', Nat.add_succ, Nat.mul_succ]
+
+@[simp] theorem range'_one {s step : Nat} : range' s 1 step = [s] := rfl
+
+@[simp] theorem length_range' (s step) : ∀ n : Nat, length (range' s n step) = n
+  | 0 => rfl
+  | _ + 1 => congrArg succ (length_range' _ _ _)
+
+@[simp] theorem range'_eq_nil : range' s n step = [] ↔ n = 0 := by
+  rw [← length_eq_zero, length_range']
+
+theorem mem_range' : ∀{n}, m ∈ range' s n step ↔ ∃ i < n, m = s + step * i
+  | 0 => by simp [range', Nat.not_lt_zero]
+  | n + 1 => by
+    have h (i) : i ≤ n ↔ i = 0 ∨ ∃ j, i = succ j ∧ j < n := by
+      cases i <;> simp [Nat.succ_le, Nat.succ_inj']
+    simp [range', mem_range', Nat.lt_succ, h]; simp only [← exists_and_right, and_assoc]
+    rw [exists_comm]; simp [Nat.mul_succ, Nat.add_assoc, Nat.add_comm]
+
+@[simp] theorem mem_range'_1 : m ∈ range' s n ↔ s ≤ m ∧ m < s + n := by
+  simp [mem_range']; exact ⟨
+    fun ⟨i, h, e⟩ => e ▸ ⟨Nat.le_add_right .., Nat.add_lt_add_left h _⟩,
+    fun ⟨h₁, h₂⟩ => ⟨m - s, Nat.sub_lt_left_of_lt_add h₁ h₂, (Nat.add_sub_cancel' h₁).symm⟩⟩
+
+theorem pairwise_lt_range' s n (step := 1) (pos : 0 < step := by simp) :
+    Pairwise (· < ·) (range' s n step) :=
+  match s, n, step, pos with
+  | _, 0, _, _ => Pairwise.nil
+  | s, n + 1, step, pos => by
+    simp only [range'_succ, pairwise_cons]
+    constructor
+    · intros n m
+      rw [mem_range'] at m
+      omega
+    · exact pairwise_lt_range' (s + step) n step pos
+
+theorem pairwise_le_range' s n (step := 1) :
+    Pairwise (· ≤ ·) (range' s n step) :=
+  match s, n, step with
+  | _, 0, _ => Pairwise.nil
+  | s, n + 1, step => by
+    simp only [range'_succ, pairwise_cons]
+    constructor
+    · intros n m
+      rw [mem_range'] at m
+      omega
+    · exact pairwise_le_range' (s + step) n step
+
+theorem nodup_range' (s n : Nat) (step := 1) (h : 0 < step := by simp) : Nodup (range' s n step) :=
+  (pairwise_lt_range' s n step h).imp Nat.ne_of_lt
+
+@[simp]
+theorem map_add_range' (a) : ∀ s n step, map (a + ·) (range' s n step) = range' (a + s) n step
+  | _, 0, _ => rfl
+  | s, n + 1, step => by simp [range', map_add_range' _ (s + step) n step, Nat.add_assoc]
+
+theorem map_sub_range' (a s n : Nat) (h : a ≤ s) :
+    map (· - a) (range' s n step) = range' (s - a) n step := by
+  conv => lhs; rw [← Nat.add_sub_cancel' h]
+  rw [← map_add_range', map_map, (?_ : _∘_ = _), map_id]
+  funext x; apply Nat.add_sub_cancel_left
+
+theorem range'_append : ∀ s m n step : Nat,
+    range' s m step ++ range' (s + step * m) n step = range' s (n + m) step
+  | s, 0, n, step => rfl
+  | s, m + 1, n, step => by
+    simpa [range', Nat.mul_succ, Nat.add_assoc, Nat.add_comm]
+      using range'_append (s + step) m n step
+
+@[simp] theorem range'_append_1 (s m n : Nat) :
+    range' s m ++ range' (s + m) n = range' s (n + m) := by simpa using range'_append s m n 1
+
+theorem range'_sublist_right {s m n : Nat} : range' s m step <+ range' s n step ↔ m ≤ n :=
+  ⟨fun h => by simpa only [length_range'] using h.length_le,
+   fun h => by rw [← Nat.sub_add_cancel h, ← range'_append]; apply sublist_append_left⟩
+
+theorem range'_subset_right {s m n : Nat} (step0 : 0 < step) :
+    range' s m step ⊆ range' s n step ↔ m ≤ n := by
+  refine ⟨fun h => Nat.le_of_not_lt fun hn => ?_, fun h => (range'_sublist_right.2 h).subset⟩
+  have ⟨i, h', e⟩ := mem_range'.1 <| h <| mem_range'.2 ⟨_, hn, rfl⟩
+  exact Nat.ne_of_gt h' (Nat.eq_of_mul_eq_mul_left step0 (Nat.add_left_cancel e))
+
+theorem range'_subset_right_1 {s m n : Nat} : range' s m ⊆ range' s n ↔ m ≤ n :=
+  range'_subset_right (by decide)
+
+theorem getElem?_range' (s step) :
+    ∀ {m n : Nat}, m < n → (range' s n step)[m]? = some (s + step * m)
+  | 0, n + 1, _ => by simp [range'_succ]
+  | m + 1, n + 1, h => by
+    simp only [range'_succ, getElem?_cons_succ]
+    exact (getElem?_range' (s + step) step (Nat.lt_of_add_lt_add_right h)).trans <| by
+      simp [Nat.mul_succ, Nat.add_assoc, Nat.add_comm]
+
+@[simp] theorem getElem_range' {n m step} (i) (H : i < (range' n m step).length) :
+    (range' n m step)[i] = n + step * i :=
+  (getElem?_eq_some.1 <| getElem?_range' n step (by simpa using H)).2
+
+theorem range'_concat (s n : Nat) : range' s (n + 1) step = range' s n step ++ [s + step * n] := by
+  rw [Nat.add_comm n 1]; exact (range'_append s n 1 step).symm
+
+theorem range'_1_concat (s n : Nat) : range' s (n + 1) = range' s n ++ [s + n] := by
+  simp [range'_concat]
+
+/-! ### range -/
+
+theorem range_loop_range' : ∀ s n : Nat, range.loop s (range' s n) = range' 0 (n + s)
+  | 0, n => rfl
+  | s + 1, n => by rw [← Nat.add_assoc, Nat.add_right_comm n s 1]; exact range_loop_range' s (n + 1)
+
+theorem range_eq_range' (n : Nat) : range n = range' 0 n :=
+  (range_loop_range' n 0).trans <| by rw [Nat.zero_add]
+
+theorem range_succ_eq_map (n : Nat) : range (n + 1) = 0 :: map succ (range n) := by
+  rw [range_eq_range', range_eq_range', range', Nat.add_comm, ← map_add_range']
+  congr; exact funext (Nat.add_comm 1)
+
+theorem reverse_range' : ∀ s n : Nat, reverse (range' s n) = map (s + n - 1 - ·) (range n)
+  | s, 0 => rfl
+  | s, n + 1 => by
+    rw [range'_1_concat, reverse_append, range_succ_eq_map,
+      show s + (n + 1) - 1 = s + n from rfl, map, map_map]
+    simp [reverse_range', Nat.sub_right_comm, Nat.sub_sub]
+
+theorem range'_eq_map_range (s n : Nat) : range' s n = map (s + ·) (range n) := by
+  rw [range_eq_range', map_add_range']; rfl
+
+@[simp] theorem length_range (n : Nat) : length (range n) = n := by
+  simp only [range_eq_range', length_range']
+
+@[simp] theorem range_eq_nil {n : Nat} : range n = [] ↔ n = 0 := by
+  rw [← length_eq_zero, length_range]
+
+@[simp]
+theorem range_sublist {m n : Nat} : range m <+ range n ↔ m ≤ n := by
+  simp only [range_eq_range', range'_sublist_right]
+
+@[simp]
+theorem range_subset {m n : Nat} : range m ⊆ range n ↔ m ≤ n := by
+  simp only [range_eq_range', range'_subset_right, lt_succ_self]
+
+@[simp]
+theorem mem_range {m n : Nat} : m ∈ range n ↔ m < n := by
+  simp only [range_eq_range', mem_range'_1, Nat.zero_le, true_and, Nat.zero_add]
+
+theorem not_mem_range_self {n : Nat} : n ∉ range n := by simp
+
+theorem self_mem_range_succ (n : Nat) : n ∈ range (n + 1) := by simp
+
+theorem pairwise_lt_range (n : Nat) : Pairwise (· < ·) (range n) := by
+  simp (config := {decide := true}) only [range_eq_range', pairwise_lt_range']
+
+theorem pairwise_le_range (n : Nat) : Pairwise (· ≤ ·) (range n) :=
+  Pairwise.imp Nat.le_of_lt (pairwise_lt_range _)
+
+theorem getElem?_range {m n : Nat} (h : m < n) : (range n)[m]? = some m := by
+  simp [range_eq_range', getElem?_range' _ _ h]
+
+@[simp] theorem getElem_range {n : Nat} (m) (h : m < (range n).length) : (range n)[m] = m := by
+  simp [range_eq_range']
+
+theorem range_succ (n : Nat) : range (succ n) = range n ++ [n] := by
+  simp only [range_eq_range', range'_1_concat, Nat.zero_add]
+
+theorem range_add (a b : Nat) : range (a + b) = range a ++ (range b).map (a + ·) := by
+  rw [← range'_eq_map_range]
+  simpa [range_eq_range', Nat.add_comm] using (range'_append_1 0 a b).symm
+
+theorem take_range (m n : Nat) : take m (range n) = range (min m n) := by
+  apply List.ext_getElem
+  · simp
+  · simp (config := { contextual := true }) [← getElem_take, Nat.lt_min]
+
+theorem nodup_range (n : Nat) : Nodup (range n) := by
+  simp (config := {decide := true}) only [range_eq_range', nodup_range']
+
+/-! ### iota -/
+
+theorem iota_eq_reverse_range' : ∀ n : Nat, iota n = reverse (range' 1 n)
+  | 0 => rfl
+  | n + 1 => by simp [iota, range'_concat, iota_eq_reverse_range' n, reverse_append, Nat.add_comm]
+
+@[simp] theorem length_iota (n : Nat) : length (iota n) = n := by simp [iota_eq_reverse_range']
+
+@[simp]
+theorem mem_iota {m n : Nat} : m ∈ iota n ↔ 1 ≤ m ∧ m ≤ n := by
+  simp [iota_eq_reverse_range', Nat.add_comm, Nat.lt_succ]
+
+theorem pairwise_gt_iota (n : Nat) : Pairwise (· > ·) (iota n) := by
+  simpa only [iota_eq_reverse_range', pairwise_reverse] using pairwise_lt_range' 1 n
+
+theorem nodup_iota (n : Nat) : Nodup (iota n) :=
+  (pairwise_gt_iota n).imp Nat.ne_of_gt
+
+/-! ### enumFrom -/
+
+@[simp]
+theorem enumFrom_singleton (x : α) (n : Nat) : enumFrom n [x] = [(n, x)] :=
+  rfl
+
+theorem mk_add_mem_enumFrom_iff_getElem? {n i : Nat} {x : α} {l : List α} :
+    (n + i, x) ∈ enumFrom n l ↔ l[i]? = some x := by
+  simp [mem_iff_get?]
+
+theorem mk_mem_enumFrom_iff_le_and_getElem?_sub {n i : Nat} {x : α} {l : List α} :
+    (i, x) ∈ enumFrom n l ↔ n ≤ i ∧ l[i - n]? = x := by
+  if h : n ≤ i then
+    rcases Nat.exists_eq_add_of_le h with ⟨i, rfl⟩
+    simp [mk_add_mem_enumFrom_iff_getElem?, Nat.add_sub_cancel_left]
+  else
+    have : ∀ k, n + k ≠ i := by rintro k rfl; simp at h
+    simp [h, mem_iff_get?, this]
+
+theorem le_fst_of_mem_enumFrom {x : Nat × α} {n : Nat} {l : List α} (h : x ∈ enumFrom n l) :
+    n ≤ x.1 :=
+  (mk_mem_enumFrom_iff_le_and_getElem?_sub.1 h).1
+
+theorem fst_lt_add_of_mem_enumFrom {x : Nat × α} {n : Nat} {l : List α} (h : x ∈ enumFrom n l) :
+    x.1 < n + length l := by
+  rcases mem_iff_get.1 h with ⟨i, rfl⟩
+  simpa using i.isLt
+
+theorem map_enumFrom (f : α → β) (n : Nat) (l : List α) :
+    map (Prod.map id f) (enumFrom n l) = enumFrom n (map f l) := by
+  induction l generalizing n <;> simp_all
+
+@[simp]
+theorem enumFrom_map_fst (n) :
+    ∀ (l : List α), map Prod.fst (enumFrom n l) = range' n l.length
+  | [] => rfl
+  | _ :: _ => congrArg (cons _) (enumFrom_map_fst _ _)
+
+@[simp]
+theorem enumFrom_map_snd : ∀ (n) (l : List α), map Prod.snd (enumFrom n l) = l
+  | _, [] => rfl
+  | _, _ :: _ => congrArg (cons _) (enumFrom_map_snd _ _)
+
+theorem snd_mem_of_mem_enumFrom {x : Nat × α} {n : Nat} {l : List α} (h : x ∈ enumFrom n l) : x.2 ∈ l :=
+  enumFrom_map_snd n l ▸ mem_map_of_mem _ h
+
+theorem snd_eq_of_mem_enumFrom {x : Nat × α} {n : Nat} {l : List α} (h : x ∈ enumFrom n l) :
+    x.2 = l[x.1 - n]'(by have := le_fst_of_mem_enumFrom h; have := fst_lt_add_of_mem_enumFrom h; omega) := by
+  induction l generalizing n with
+  | nil => cases h
+  | cons hd tl ih =>
+    cases h with
+    | head h => simp
+    | tail h m =>
+      specialize ih m
+      have : x.1 - n = x.1 - (n + 1) + 1 := by
+        have := le_fst_of_mem_enumFrom m
+        omega
+      simp [this, ih]
+
+theorem mem_enumFrom {x : α} {i j : Nat} {xs : List α} (h : (i, x) ∈ xs.enumFrom j) :
+    j ≤ i ∧ i < j + xs.length ∧
+      x = xs[i - j]'(by have := le_fst_of_mem_enumFrom h; have := fst_lt_add_of_mem_enumFrom h; omega) :=
+  ⟨le_fst_of_mem_enumFrom h, fst_lt_add_of_mem_enumFrom h, snd_eq_of_mem_enumFrom h⟩
+
+theorem enumFrom_cons' (n : Nat) (x : α) (xs : List α) :
+    enumFrom n (x :: xs) = (n, x) :: (enumFrom n xs).map (Prod.map (· + 1) id) := by
+  rw [enumFrom_cons, Nat.add_comm, ← map_fst_add_enumFrom_eq_enumFrom]
+
+theorem enumFrom_map (n : Nat) (l : List α) (f : α → β) :
+    enumFrom n (l.map f) = (enumFrom n l).map (Prod.map id f) := by
+  induction l with
+  | nil => rfl
+  | cons hd tl IH =>
+    rw [map_cons, enumFrom_cons', enumFrom_cons', map_cons, map_map, IH, map_map]
+    rfl
+
+theorem enumFrom_append (xs ys : List α) (n : Nat) :
+    enumFrom n (xs ++ ys) = enumFrom n xs ++ enumFrom (n + xs.length) ys := by
+  induction xs generalizing ys n with
+  | nil => simp
+  | cons x xs IH =>
+    rw [cons_append, enumFrom_cons, IH, ← cons_append, ← enumFrom_cons, length, Nat.add_right_comm,
+      Nat.add_assoc]
+
+theorem enumFrom_eq_zip_range' (l : List α) {n : Nat} : l.enumFrom n = (range' n l.length).zip l :=
+  zip_of_prod (enumFrom_map_fst _ _) (enumFrom_map_snd _ _)
+
+@[simp]
+theorem unzip_enumFrom_eq_prod (l : List α) {n : Nat} :
+    (l.enumFrom n).unzip = (range' n l.length, l) := by
+  simp only [enumFrom_eq_zip_range', unzip_zip, length_range']
+
+/-! ### enum -/
+
+theorem enum_cons : (a::as).enum = (0, a) :: as.enumFrom 1 := rfl
+
+theorem enum_cons' (x : α) (xs : List α) :
+    enum (x :: xs) = (0, x) :: (enum xs).map (Prod.map (· + 1) id) :=
+  enumFrom_cons' _ _ _
+
+@[simp]
+theorem enum_eq_nil {l : List α} : List.enum l = [] ↔ l = [] := enumFrom_eq_nil
+
+@[simp] theorem enum_singleton (x : α) : enum [x] = [(0, x)] := rfl
+
+@[simp] theorem enum_length : (enum l).length = l.length :=
+  enumFrom_length
+
+@[simp]
+theorem getElem?_enum (l : List α) (n : Nat) : (enum l)[n]? = l[n]?.map fun a => (n, a) := by
+  rw [enum, getElem?_enumFrom, Nat.zero_add]
+
+@[simp]
+theorem getElem_enum (l : List α) (i : Nat) (h : i < l.enum.length) :
+    l.enum[i] = (i, l[i]'(by simpa [enum_length] using h)) := by
+  simp [enum]
+
+theorem mk_mem_enum_iff_getElem? {i : Nat} {x : α} {l : List α} : (i, x) ∈ enum l ↔ l[i]? = x := by
+  simp [enum, mk_mem_enumFrom_iff_le_and_getElem?_sub]
+
+theorem mem_enum_iff_getElem? {x : Nat × α} {l : List α} : x ∈ enum l ↔ l[x.1]? = some x.2 :=
+  mk_mem_enum_iff_getElem?
+
+theorem fst_lt_of_mem_enum {x : Nat × α} {l : List α} (h : x ∈ enum l) : x.1 < length l := by
+  simpa using fst_lt_add_of_mem_enumFrom h
+
+theorem snd_mem_of_mem_enum {x : Nat × α} {l : List α} (h : x ∈ enum l) : x.2 ∈ l :=
+  snd_mem_of_mem_enumFrom h
+
+theorem snd_eq_of_mem_enum {x : Nat × α} {l : List α} (h : x ∈ enum l) :
+    x.2 = l[x.1]'(fst_lt_of_mem_enum h) :=
+  snd_eq_of_mem_enumFrom h
+
+theorem mem_enum {x : α} {i : Nat} {xs : List α} (h : (i, x) ∈ xs.enum) :
+    i < xs.length ∧ x = xs[i]'(fst_lt_of_mem_enum h) :=
+  by simpa using mem_enumFrom h
+
+theorem map_enum (f : α → β) (l : List α) : map (Prod.map id f) (enum l) = enum (map f l) :=
+  map_enumFrom f 0 l
+
+@[simp] theorem enum_map_fst (l : List α) : map Prod.fst (enum l) = range l.length := by
+  simp only [enum, enumFrom_map_fst, range_eq_range']
+
+@[simp]
+theorem enum_map_snd (l : List α) : map Prod.snd (enum l) = l :=
+  enumFrom_map_snd _ _
+
+theorem enum_map (l : List α) (f : α → β) : (l.map f).enum = l.enum.map (Prod.map id f) :=
+  enumFrom_map _ _ _
+
+theorem enum_append (xs ys : List α) : enum (xs ++ ys) = enum xs ++ enumFrom xs.length ys := by
+  simp [enum, enumFrom_append]
+
+theorem enum_eq_zip_range (l : List α) : l.enum = (range l.length).zip l :=
+  zip_of_prod (enum_map_fst _) (enum_map_snd _)
+
+@[simp]
+theorem unzip_enum_eq_prod (l : List α) : l.enum.unzip = (range l.length, l) := by
+  simp only [enum_eq_zip_range, unzip_zip, length_range]
+
+end List

src/Init/Data/List/Nat/Sublist.lean

@@ -0,0 +1,129 @@
+/-
+Copyright (c) 2024 Lean FRO. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Kim Morrison
+-/
+prelude
+import Init.Data.List.Sublist
+import Init.Data.List.Nat.Basic
+import Init.Data.List.Nat.TakeDrop
+import Init.Data.Nat.Lemmas
+
+/-!
+# Further lemmas about `List.IsSuffix` / `List.IsPrefix` / `List.IsInfix`.
+
+These are in a separate file from most of the lemmas about `List.IsSuffix`
+as they required importing more lemmas about natural numbers, and use `omega`.
+-/
+
+namespace List
+
+theorem IsSuffix.getElem {x y : List α} (h : x <:+ y) {n} (hn : n < x.length) :
+    x[n] = y[y.length - x.length + n]'(by have := h.length_le; omega) := by
+  rw [getElem_eq_getElem_reverse, h.reverse.getElem, getElem_reverse]
+  congr
+  have := h.length_le
+  omega
+
+theorem isSuffix_iff : l₁ <:+ l₂ ↔
+    l₁.length ≤ l₂.length ∧ ∀ i (h : i < l₁.length), l₂[i + l₂.length - l₁.length]? = some l₁[i] := by
+  suffices l₁.length ≤ l₂.length ∧ l₁ <:+ l₂ ↔
+      l₁.length ≤ l₂.length ∧ ∀ i (h : i < l₁.length), l₂[i + l₂.length - l₁.length]? = some l₁[i] by
+    constructor
+    · intro h
+      exact this.mp ⟨h.length_le, h⟩
+    · intro h
+      exact (this.mpr h).2
+  simp only [and_congr_right_iff]
+  intro le
+  rw [← reverse_prefix, isPrefix_iff]
+  simp only [length_reverse]
+  constructor
+  · intro w i h
+    specialize w (l₁.length - 1 - i) (by omega)
+    rw [getElem?_reverse (by omega)] at w
+    have p : l₂.length - 1 - (l₁.length - 1 - i) = i + l₂.length - l₁.length := by omega
+    rw [p] at w
+    rw [w, getElem_reverse]
+    congr
+    omega
+  · intro w i h
+    rw [getElem?_reverse]
+    specialize w (l₁.length - 1 - i) (by omega)
+    have p : l₁.length - 1 - i + l₂.length - l₁.length = l₂.length - 1 - i := by omega
+    rw [p] at w
+    rw [w, getElem_reverse]
+    exact Nat.lt_of_lt_of_le h le
+
+theorem isInfix_iff : l₁ <:+: l₂ ↔
+    ∃ k, l₁.length + k ≤ l₂.length ∧ ∀ i (h : i < l₁.length), l₂[i + k]? = some l₁[i] := by
+  constructor
+  · intro h
+    obtain ⟨t, p, s⟩ := infix_iff_suffix_prefix.mp h
+    refine ⟨t.length - l₁.length, by have := p.length_le; have := s.length_le; omega, ?_⟩
+    rw [isSuffix_iff] at p
+    obtain ⟨p', p⟩ := p
+    rw [isPrefix_iff] at s
+    intro i h
+    rw [s _ (by omega)]
+    specialize p i (by omega)
+    rw [Nat.add_sub_assoc (by omega)] at p
+    rw [← getElem?_eq_getElem, p]
+  · rintro ⟨k, le, w⟩
+    refine ⟨l₂.take k, l₂.drop (k + l₁.length), ?_⟩
+    ext1 i
+    rw [getElem?_append]
+    split
+    · rw [getElem?_append]
+      split
+      · rw [getElem?_take]; simp_all; omega
+      · simp_all
+        have p : i = (i - k) + k := by omega
+        rw [p, w _ (by omega), getElem?_eq_getElem]
+        · congr 2
+          omega
+        · omega
+    · rw [getElem?_drop]
+      congr
+      simp_all
+      omega
+
+theorem suffix_iff_eq_append : l₁ <:+ l₂ ↔ take (length l₂ - length l₁) l₂ ++ l₁ = l₂ :=
+  ⟨by rintro ⟨r, rfl⟩; simp only [length_append, Nat.add_sub_cancel_right, take_left], fun e =>
+    ⟨_, e⟩⟩
+
+theorem prefix_take_iff {x y : List α} {n : Nat} : x <+: y.take n ↔ x <+: y ∧ x.length ≤ n := by
+  constructor
+  · intro h
+    constructor
+    · exact List.IsPrefix.trans h <| List.take_prefix n y
+    · replace h := h.length_le
+      rw [length_take, Nat.le_min] at h
+      exact h.left
+  · intro ⟨hp, hl⟩
+    have hl' := hp.length_le
+    rw [List.prefix_iff_eq_take] at *
+    rw [hp, List.take_take]
+    simp [Nat.min_eq_left, hl, hl']
+
+theorem suffix_iff_eq_drop : l₁ <:+ l₂ ↔ l₁ = drop (length l₂ - length l₁) l₂ :=
+  ⟨fun h => append_cancel_left <| (suffix_iff_eq_append.1 h).trans (take_append_drop _ _).symm,
+    fun e => e.symm ▸ drop_suffix _ _⟩
+
+theorem prefix_take_le_iff {L : List α} (hm : m < L.length) :
+    L.take m <+: L.take n ↔ m ≤ n := by
+  simp only [prefix_iff_eq_take, length_take]
+  induction m generalizing L n with
+  | zero => simp [Nat.min_eq_left, eq_self_iff_true, Nat.zero_le, take]
+  | succ m IH =>
+    cases L with
+    | nil => simp_all
+    | cons l ls =>
+      cases n with
+      | zero =>
+        simp
+      | succ n =>
+        simp only [length_cons, Nat.succ_eq_add_one, Nat.add_lt_add_iff_right] at hm
+        simp [← @IH n ls hm, Nat.min_eq_left, Nat.le_of_lt hm]
+
+end List

src/Init/Data/List/Nat/TakeDrop.lean

@@ -0,0 +1,544 @@
+/-
+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.Zip
+import Init.Data.List.Sublist
+import Init.Data.Nat.Lemmas
+
+/-!
+# Further lemmas about `List.take`, `List.drop`, `List.zip` and `List.zipWith`.
+
+These are in a separate file from most of the list lemmas
+as they required importing more lemmas about natural numbers, and use `omega`.
+-/
+
+namespace List
+
+open Nat
+
+/-! ### take -/
+
+@[simp] theorem length_take : ∀ (i : Nat) (l : List α), length (take i l) = min i (length l)
+  | 0, l => by simp [Nat.zero_min]
+  | succ n, [] => by simp [Nat.min_zero]
+  | succ n, _ :: l => by simp [Nat.succ_min_succ, length_take]
+
+theorem length_take_le (n) (l : List α) : length (take n l) ≤ n := by simp [Nat.min_le_left]
+
+theorem length_take_le' (n) (l : List α) : length (take n l) ≤ l.length :=
+  by simp [Nat.min_le_right]
+
+theorem length_take_of_le (h : n ≤ length l) : length (take n l) = n := by simp [Nat.min_eq_left h]
+
+/-- The `i`-th element of a list coincides with the `i`-th element of any of its prefixes of
+length `> i`. Version designed to rewrite from the big list to the small list. -/
+theorem getElem_take (L : List α) {i j : Nat} (hi : i < L.length) (hj : i < j) :
+    L[i] = (L.take j)[i]'(length_take .. ▸ Nat.lt_min.mpr ⟨hj, hi⟩) :=
+  getElem_of_eq (take_append_drop j L).symm _ ▸ getElem_append ..
+
+/-- The `i`-th element of a list coincides with the `i`-th element of any of its prefixes of
+length `> i`. Version designed to rewrite from the small list to the big list. -/
+theorem getElem_take' (L : List α) {j i : Nat} {h : i < (L.take j).length} :
+    (L.take j)[i] =
+    L[i]'(Nat.lt_of_lt_of_le h (length_take_le' _ _)) := by
+  rw [length_take, Nat.lt_min] at h; rw [getElem_take L _ h.1]
+
+/-- The `i`-th element of a list coincides with the `i`-th element of any of its prefixes of
+length `> i`. Version designed to rewrite from the big list to the small list. -/
+@[deprecated getElem_take (since := "2024-06-12")]
+theorem get_take (L : List α) {i j : Nat} (hi : i < L.length) (hj : i < j) :
+    get L ⟨i, hi⟩ = get (L.take j) ⟨i, length_take .. ▸ Nat.lt_min.mpr ⟨hj, hi⟩⟩ := by
+  simp [getElem_take _ hi hj]
+
+/-- The `i`-th element of a list coincides with the `i`-th element of any of its prefixes of
+length `> i`. Version designed to rewrite from the small list to the big list. -/
+@[deprecated getElem_take (since := "2024-06-12")]
+theorem get_take' (L : List α) {j i} :
+    get (L.take j) i =
+    get L ⟨i.1, Nat.lt_of_lt_of_le i.2 (length_take_le' _ _)⟩ := by
+  simp [getElem_take']
+
+theorem getElem?_take_eq_none {l : List α} {n m : Nat} (h : n ≤ m) :
+    (l.take n)[m]? = none :=
+  getElem?_eq_none <| Nat.le_trans (length_take_le _ _) h
+
+@[deprecated getElem?_take_eq_none (since := "2024-06-12")]
+theorem get?_take_eq_none {l : List α} {n m : Nat} (h : n ≤ m) :
+    (l.take n).get? m = none := by
+  simp [getElem?_take_eq_none h]
+
+theorem getElem?_take {l : List α} {n m : Nat} :
+    (l.take n)[m]? = if m < n then l[m]? else none := by
+  split
+  · next h => exact getElem?_take_of_lt h
+  · next h => exact getElem?_take_eq_none (Nat.le_of_not_lt h)
+
+@[deprecated getElem?_take (since := "2024-06-12")]
+theorem get?_take_eq_if {l : List α} {n m : Nat} :
+    (l.take n).get? m = if m < n then l.get? m else none := by
+  simp [getElem?_take]
+
+theorem head?_take {l : List α} {n : Nat} :
+    (l.take n).head? = if n = 0 then none else l.head? := by
+  simp [head?_eq_getElem?, getElem?_take]
+  split
+  · rw [if_neg (by omega)]
+  · rw [if_pos (by omega)]
+
+theorem head_take {l : List α} {n : Nat} (h : l.take n ≠ []) :
+    (l.take n).head h = l.head (by simp_all) := by
+  apply Option.some_inj.1
+  rw [← head?_eq_head, ← head?_eq_head, head?_take, if_neg]
+  simp_all
+
+theorem getLast?_take {l : List α} : (l.take n).getLast? = if n = 0 then none else l[n - 1]?.or l.getLast? := by
+  rw [getLast?_eq_getElem?, getElem?_take, length_take]
+  split
+  · rw [if_neg (by omega)]
+    rw [Nat.min_def]
+    split
+    · rw [getElem?_eq_getElem (by omega)]
+      simp
+    · rw [← getLast?_eq_getElem?, getElem?_eq_none (by omega)]
+      simp
+  · rw [if_pos]
+    omega
+
+theorem getLast_take {l : List α} (h : l.take n ≠ []) :
+    (l.take n).getLast h = l[n - 1]?.getD (l.getLast (by simp_all)) := by
+  rw [getLast_eq_getElem, getElem_take']
+  simp [length_take, Nat.min_def]
+  simp at h
+  split
+  · rw [getElem?_eq_getElem (by omega)]
+    simp
+  · rw [getElem?_eq_none (by omega), getLast_eq_getElem]
+    simp
+
+theorem take_take : ∀ (n m) (l : List α), take n (take m l) = take (min n m) l
+  | n, 0, l => by rw [Nat.min_zero, take_zero, take_nil]
+  | 0, m, l => by rw [Nat.zero_min, take_zero, take_zero]
+  | succ n, succ m, nil => by simp only [take_nil]
+  | succ n, succ m, a :: l => by
+    simp only [take, succ_min_succ, take_take n m l]
+
+theorem take_set_of_lt (a : α) {n m : Nat} (l : List α) (h : m < n) :
+    (l.set n a).take m = l.take m :=
+  List.ext_getElem? fun i => by
+    rw [getElem?_take, getElem?_take]
+    split
+    · next h' => rw [getElem?_set_ne (by omega)]
+    · rfl
+
+@[simp] theorem take_replicate (a : α) : ∀ n m : Nat, take n (replicate m a) = replicate (min n m) a
+  | n, 0 => by simp [Nat.min_zero]
+  | 0, m => by simp [Nat.zero_min]
+  | succ n, succ m => by simp [replicate_succ, succ_min_succ, take_replicate]
+
+@[simp] theorem drop_replicate (a : α) : ∀ n m : Nat, drop n (replicate m a) = replicate (m - n) a
+  | n, 0 => by simp
+  | 0, m => by simp
+  | succ n, succ m => by simp [replicate_succ, succ_sub_succ, drop_replicate]
+
+/-- Taking the first `n` elements in `l₁ ++ l₂` is the same as appending the first `n` elements
+of `l₁` to the first `n - l₁.length` elements of `l₂`. -/
+theorem take_append_eq_append_take {l₁ l₂ : List α} {n : Nat} :
+    take n (l₁ ++ l₂) = take n l₁ ++ take (n - l₁.length) l₂ := by
+  induction l₁ generalizing n
+  · simp
+  · cases n
+    · simp [*]
+    · simp only [cons_append, take_succ_cons, length_cons, succ_eq_add_one, cons.injEq,
+        append_cancel_left_eq, true_and, *]
+      congr 1
+      omega
+
+theorem take_append_of_le_length {l₁ l₂ : List α} {n : Nat} (h : n ≤ l₁.length) :
+    (l₁ ++ l₂).take n = l₁.take n := by
+  simp [take_append_eq_append_take, Nat.sub_eq_zero_of_le h]
+
+/-- Taking the first `l₁.length + i` elements in `l₁ ++ l₂` is the same as appending the first
+`i` elements of `l₂` to `l₁`. -/
+theorem take_append {l₁ l₂ : List α} (i : Nat) :
+    take (l₁.length + i) (l₁ ++ l₂) = l₁ ++ take i l₂ := by
+  rw [take_append_eq_append_take, take_of_length_le (Nat.le_add_right _ _), Nat.add_sub_cancel_left]
+
+@[simp]
+theorem take_eq_take :
+    ∀ {l : List α} {m n : Nat}, l.take m = l.take n ↔ min m l.length = min n l.length
+  | [], m, n => by simp [Nat.min_zero]
+  | _ :: xs, 0, 0 => by simp
+  | x :: xs, m + 1, 0 => by simp [Nat.zero_min, succ_min_succ]
+  | x :: xs, 0, n + 1 => by simp [Nat.zero_min, succ_min_succ]
+  | x :: xs, m + 1, n + 1 => by simp [succ_min_succ, take_eq_take]
+
+theorem take_add (l : List α) (m n : Nat) : l.take (m + n) = l.take m ++ (l.drop m).take n := by
+  suffices take (m + n) (take m l ++ drop m l) = take m l ++ take n (drop m l) by
+    rw [take_append_drop] at this
+    assumption
+  rw [take_append_eq_append_take, take_of_length_le, append_right_inj]
+  · simp only [take_eq_take, length_take, length_drop]
+    omega
+  apply Nat.le_trans (m := m)
+  · apply length_take_le
+  · apply Nat.le_add_right
+
+theorem dropLast_take {n : Nat} {l : List α} (h : n < l.length) :
+    (l.take n).dropLast = l.take (n - 1) := by
+  simp only [dropLast_eq_take, length_take, Nat.le_of_lt h, Nat.min_eq_left, take_take, sub_le]
+
+theorem map_eq_append_split {f : α → β} {l : List α} {s₁ s₂ : List β}
+    (h : map f l = s₁ ++ s₂) : ∃ l₁ l₂, l = l₁ ++ l₂ ∧ map f l₁ = s₁ ∧ map f l₂ = s₂ := by
+  have := h
+  rw [← take_append_drop (length s₁) l] at this ⊢
+  rw [map_append] at this
+  refine ⟨_, _, rfl, append_inj this ?_⟩
+  rw [length_map, length_take, Nat.min_eq_left]
+  rw [← length_map l f, h, length_append]
+  apply Nat.le_add_right
+
+theorem take_prefix_take_left (l : List α) {m n : Nat} (h : m ≤ n) : take m l <+: take n l := by
+  rw [isPrefix_iff]
+  intro i w
+  rw [getElem?_take_of_lt, getElem_take', getElem?_eq_getElem]
+  simp only [length_take] at w
+  exact Nat.lt_of_lt_of_le (Nat.lt_of_lt_of_le w (Nat.min_le_left _ _)) h
+
+theorem take_sublist_take_left (l : List α) {m n : Nat} (h : m ≤ n) : take m l <+ take n l :=
+  (take_prefix_take_left l h).sublist
+
+theorem take_subset_take_left (l : List α) {m n : Nat} (h : m ≤ n) : take m l ⊆ take n l :=
+  (take_sublist_take_left l h).subset
+
+/-! ### drop -/
+
+theorem lt_length_drop (L : List α) {i j : Nat} (h : i + j < L.length) : j < (L.drop i).length := by
+  have A : i < L.length := Nat.lt_of_le_of_lt (Nat.le.intro rfl) h
+  rw [(take_append_drop i L).symm] at h
+  simpa only [Nat.le_of_lt A, Nat.min_eq_left, Nat.add_lt_add_iff_left, length_take,
+    length_append] using h
+
+/-- The `i + j`-th element of a list coincides with the `j`-th element of the list obtained by
+dropping the first `i` elements. Version designed to rewrite from the big list to the small list. -/
+theorem getElem_drop (L : List α) {i j : Nat} (h : i + j < L.length) :
+    L[i + j] = (L.drop i)[j]'(lt_length_drop L h) := by
+  have : i ≤ L.length := Nat.le_trans (Nat.le_add_right _ _) (Nat.le_of_lt h)
+  rw [getElem_of_eq (take_append_drop i L).symm h, getElem_append_right'] <;>
+    simp [Nat.min_eq_left this, Nat.add_sub_cancel_left, Nat.le_add_right]
+
+/-- The `i + j`-th element of a list coincides with the `j`-th element of the list obtained by
+dropping the first `i` elements. Version designed to rewrite from the big list to the small list. -/
+@[deprecated getElem_drop (since := "2024-06-12")]
+theorem get_drop (L : List α) {i j : Nat} (h : i + j < L.length) :
+    get L ⟨i + j, h⟩ = get (L.drop i) ⟨j, lt_length_drop L h⟩ := by
+  simp [getElem_drop]
+
+/-- The `i + j`-th element of a list coincides with the `j`-th element of the list obtained by
+dropping the first `i` elements. Version designed to rewrite from the small list to the big list. -/
+theorem getElem_drop' (L : List α) {i : Nat} {j : Nat} {h : j < (L.drop i).length} :
+    (L.drop i)[j] = L[i + j]'(by
+      rw [Nat.add_comm]
+      exact Nat.add_lt_of_lt_sub (length_drop i L ▸ h)) := by
+  rw [getElem_drop]
+
+/-- The `i + j`-th element of a list coincides with the `j`-th element of the list obtained by
+dropping the first `i` elements. Version designed to rewrite from the small list to the big list. -/
+@[deprecated getElem_drop' (since := "2024-06-12")]
+theorem get_drop' (L : List α) {i j} :
+    get (L.drop i) j = get L ⟨i + j, by
+      rw [Nat.add_comm]
+      exact Nat.add_lt_of_lt_sub (length_drop i L ▸ j.2)⟩ := by
+  simp [getElem_drop']
+
+@[simp]
+theorem getElem?_drop (L : List α) (i j : Nat) : (L.drop i)[j]? = L[i + j]? := by
+  ext
+  simp only [getElem?_eq_some, getElem_drop', Option.mem_def]
+  constructor <;> intro ⟨h, ha⟩
+  · exact ⟨_, ha⟩
+  · refine ⟨?_, ha⟩
+    rw [length_drop]
+    rw [Nat.add_comm] at h
+    apply Nat.lt_sub_of_add_lt h
+
+@[deprecated getElem?_drop (since := "2024-06-12")]
+theorem get?_drop (L : List α) (i j : Nat) : get? (L.drop i) j = get? L (i + j) := by
+  simp
+
+theorem head?_drop (l : List α) (n : Nat) :
+    (l.drop n).head? = l[n]? := by
+  rw [head?_eq_getElem?, getElem?_drop, Nat.add_zero]
+
+theorem head_drop {l : List α} {n : Nat} (h : l.drop n ≠ []) :
+    (l.drop n).head h = l[n]'(by simp_all) := by
+  have w : n < l.length := length_lt_of_drop_ne_nil h
+  simpa [head?_eq_head, getElem?_eq_getElem, h, w] using head?_drop l n
+
+theorem getLast?_drop {l : List α} : (l.drop n).getLast? = if l.length ≤ n then none else l.getLast? := by
+  rw [getLast?_eq_getElem?, getElem?_drop]
+  rw [length_drop]
+  split
+  · rw [getElem?_eq_none (by omega)]
+  · rw [getLast?_eq_getElem?]
+    congr
+    omega
+
+theorem getLast_drop {l : List α} (h : l.drop n ≠ []) :
+    (l.drop n).getLast h = l.getLast (ne_nil_of_length_pos (by simp at h; omega)) := by
+  simp only [ne_eq, drop_eq_nil_iff_le] at h
+  apply Option.some_inj.1
+  simp only [← getLast?_eq_getLast, getLast?_drop, ite_eq_right_iff]
+  omega
+
+theorem drop_length_cons {l : List α} (h : l ≠ []) (a : α) :
+    (a :: l).drop l.length = [l.getLast h] := by
+  induction l generalizing a with
+  | nil =>
+    cases h rfl
+  | cons y l ih =>
+    simp only [drop, length]
+    by_cases h₁ : l = []
+    · simp [h₁]
+    rw [getLast_cons h₁]
+    exact ih h₁ y
+
+/-- Dropping the elements up to `n` in `l₁ ++ l₂` is the same as dropping the elements up to `n`
+in `l₁`, dropping the elements up to `n - l₁.length` in `l₂`, and appending them. -/
+theorem drop_append_eq_append_drop {l₁ l₂ : List α} {n : Nat} :
+    drop n (l₁ ++ l₂) = drop n l₁ ++ drop (n - l₁.length) l₂ := by
+  induction l₁ generalizing n
+  · simp
+  · cases n
+    · simp [*]
+    · simp only [cons_append, drop_succ_cons, length_cons, succ_eq_add_one, append_cancel_left_eq, *]
+      congr 1
+      omega
+
+theorem drop_append_of_le_length {l₁ l₂ : List α} {n : Nat} (h : n ≤ l₁.length) :
+    (l₁ ++ l₂).drop n = l₁.drop n ++ l₂ := by
+  simp [drop_append_eq_append_drop, Nat.sub_eq_zero_of_le h]
+
+/-- Dropping the elements up to `l₁.length + i` in `l₁ + l₂` is the same as dropping the elements
+up to `i` in `l₂`. -/
+@[simp]
+theorem drop_append {l₁ l₂ : List α} (i : Nat) : drop (l₁.length + i) (l₁ ++ l₂) = drop i l₂ := by
+  rw [drop_append_eq_append_drop, drop_eq_nil_of_le] <;>
+    simp [Nat.add_sub_cancel_left, Nat.le_add_right]
+
+theorem set_eq_take_append_cons_drop {l : List α} {n : Nat} {a : α} :
+    l.set n a = if n < l.length then l.take n ++ a :: l.drop (n + 1) else l := by
+  split <;> rename_i h
+  · ext1 m
+    by_cases h' : m < n
+    · rw [getElem?_append_left (by simp [length_take]; omega), getElem?_set_ne (by omega),
+        getElem?_take_of_lt h']
+    · by_cases h'' : m = n
+      · subst h''
+        rw [getElem?_set_eq ‹_›, getElem?_append_right, length_take,
+          Nat.min_eq_left (by omega), Nat.sub_self, getElem?_cons_zero]
+        rw [length_take]
+        exact Nat.min_le_left m l.length
+      · have h''' : n < m := by omega
+        rw [getElem?_set_ne (by omega), getElem?_append_right, length_take,
+          Nat.min_eq_left (by omega)]
+        · obtain ⟨k, rfl⟩ := Nat.exists_eq_add_of_lt h'''
+          have p : n + k + 1 - n = k + 1 := by omega
+          rw [p]
+          rw [getElem?_cons_succ, getElem?_drop]
+          congr 1
+          omega
+        · rw [length_take]
+          exact Nat.le_trans (Nat.min_le_left _ _) (by omega)
+  · rw [set_eq_of_length_le]
+    omega
+
+theorem exists_of_set {n : Nat} {a' : α} {l : List α} (h : n < l.length) :
+    ∃ l₁ l₂, l = l₁ ++ l[n] :: l₂ ∧ l₁.length = n ∧ l.set n a' = l₁ ++ a' :: l₂ := by
+  refine ⟨l.take n, l.drop (n + 1), ⟨by simp, ⟨length_take_of_le (Nat.le_of_lt h), ?_⟩⟩⟩
+  simp [set_eq_take_append_cons_drop, h]
+
+theorem drop_set_of_lt (a : α) {n m : Nat} (l : List α)
+    (hnm : n < m) : drop m (l.set n a) = l.drop m :=
+  ext_getElem? fun k => by simpa only [getElem?_drop] using getElem?_set_ne (by omega)
+
+theorem drop_take : ∀ (m n : Nat) (l : List α), drop n (take m l) = take (m - n) (drop n l)
+  | 0, _, _ => by simp
+  | _, 0, _ => by simp
+  | _, _, [] => by simp
+  | m+1, n+1, h :: t => by
+    simp [take_succ_cons, drop_succ_cons, drop_take m n t]
+    congr 1
+    omega
+
+theorem take_reverse {α} {xs : List α} {n : Nat} :
+    xs.reverse.take n = (xs.drop (xs.length - n)).reverse := by
+  by_cases h : n ≤ xs.length
+  · induction xs generalizing n <;>
+      simp only [reverse_cons, drop, reverse_nil, Nat.zero_sub, length, take_nil]
+    next xs_hd xs_tl xs_ih =>
+    cases Nat.lt_or_eq_of_le h with
+    | inl h' =>
+      have h' := Nat.le_of_succ_le_succ h'
+      rw [take_append_of_le_length, xs_ih h']
+      rw [show xs_tl.length + 1 - n = succ (xs_tl.length - n) from _, drop]
+      · rwa [succ_eq_add_one, Nat.sub_add_comm]
+      · rwa [length_reverse]
+    | inr h' =>
+      subst h'
+      rw [length, Nat.sub_self, drop]
+      suffices xs_tl.length + 1 = (xs_tl.reverse ++ [xs_hd]).length by
+        rw [this, take_length, reverse_cons]
+      rw [length_append, length_reverse]
+      rfl
+  · have w : xs.length - n = 0 := by omega
+    rw [take_of_length_le, w, drop_zero]
+    simp
+    omega
+
+theorem drop_reverse {α} {xs : List α} {n : Nat} :
+    xs.reverse.drop n = (xs.take (xs.length - n)).reverse := by
+  by_cases h : n ≤ xs.length
+  · conv =>
+      rhs
+      rw [← reverse_reverse xs]
+    rw [← reverse_reverse xs] at h
+    generalize xs.reverse = xs' at h ⊢
+    rw [take_reverse]
+    · simp only [length_reverse, reverse_reverse] at *
+      congr
+      omega
+  · have w : xs.length - n = 0 := by omega
+    rw [drop_of_length_le, w, take_zero, reverse_nil]
+    simp
+    omega
+
+theorem reverse_take {l : List α} {n : Nat} :
+    (l.take n).reverse = l.reverse.drop (l.length - n) := by
+  by_cases h : n ≤ l.length
+  · rw [drop_reverse]
+    congr
+    omega
+  · have w : l.length - n = 0 := by omega
+    rw [w, drop_zero, take_of_length_le]
+    omega
+
+theorem reverse_drop {l : List α} {n : Nat} :
+    (l.drop n).reverse = l.reverse.take (l.length - n) := by
+  by_cases h : n ≤ l.length
+  · rw [take_reverse]
+    congr
+    omega
+  · have w : l.length - n = 0 := by omega
+    rw [w, take_zero, drop_of_length_le, reverse_nil]
+    omega
+
+/-! ### rotateLeft -/
+
+@[simp] theorem rotateLeft_replicate (n) (a : α) : rotateLeft (replicate m a) n = replicate m a := by
+  cases n with
+  | zero => simp
+  | succ n =>
+    suffices 1 < m → m - (n + 1) % m + min ((n + 1) % m) m = m by
+      simpa [rotateLeft]
+    intro h
+    rw [Nat.min_eq_left (Nat.le_of_lt (Nat.mod_lt _ (by omega)))]
+    have : (n + 1) % m < m := Nat.mod_lt _ (by omega)
+    omega
+
+/-! ### rotateRight -/
+
+@[simp] theorem rotateRight_replicate (n) (a : α) : rotateRight (replicate m a) n = replicate m a := by
+  cases n with
+  | zero => simp
+  | succ n =>
+    suffices 1 < m → m - (m - (n + 1) % m) + min (m - (n + 1) % m) m = m by
+      simpa [rotateRight]
+    intro h
+    have : (n + 1) % m < m := Nat.mod_lt _ (by omega)
+    rw [Nat.min_eq_left (by omega)]
+    omega
+
+/-! ### zipWith -/
+
+@[simp] theorem length_zipWith (f : α → β → γ) (l₁ l₂) :
+    length (zipWith f l₁ l₂) = min (length l₁) (length l₂) := by
+  induction l₁ generalizing l₂ <;> cases l₂ <;>
+    simp_all [succ_min_succ, Nat.zero_min, Nat.min_zero]
+
+theorem lt_length_left_of_zipWith {f : α → β → γ} {i : Nat} {l : List α} {l' : List β}
+    (h : i < (zipWith f l l').length) : i < l.length := by rw [length_zipWith] at h; omega
+
+theorem lt_length_right_of_zipWith {f : α → β → γ} {i : Nat} {l : List α} {l' : List β}
+    (h : i < (zipWith f l l').length) : i < l'.length := by rw [length_zipWith] at h; omega
+
+@[simp]
+theorem getElem_zipWith {f : α → β → γ} {l : List α} {l' : List β}
+    {i : Nat} {h : i < (zipWith f l l').length} :
+    (zipWith f l l')[i] =
+      f (l[i]'(lt_length_left_of_zipWith h))
+        (l'[i]'(lt_length_right_of_zipWith h)) := by
+  rw [← Option.some_inj, ← getElem?_eq_getElem, getElem?_zipWith_eq_some]
+  exact
+    ⟨l[i]'(lt_length_left_of_zipWith h), l'[i]'(lt_length_right_of_zipWith h),
+      by rw [getElem?_eq_getElem], by rw [getElem?_eq_getElem]; exact ⟨rfl, rfl⟩⟩
+
+theorem zipWith_eq_zipWith_take_min : ∀ (l₁ : List α) (l₂ : List β),
+    zipWith f l₁ l₂ = zipWith f (l₁.take (min l₁.length l₂.length)) (l₂.take (min l₁.length l₂.length))
+  | [], _ => by simp
+  | _, [] => by simp
+  | a :: l₁, b :: l₂ => by simp [succ_min_succ, zipWith_eq_zipWith_take_min l₁ l₂]
+
+theorem reverse_zipWith (h : l.length = l'.length) :
+    (zipWith f l l').reverse = zipWith f l.reverse l'.reverse := by
+  induction l generalizing l' with
+  | nil => simp
+  | cons hd tl hl =>
+    cases l' with
+    | nil => simp
+    | cons hd' tl' =>
+      simp only [Nat.add_right_cancel_iff, length] at h
+      have : tl.reverse.length = tl'.reverse.length := by simp [h]
+      simp [hl h, zipWith_append _ _ _ _ _ this]
+
+@[deprecated reverse_zipWith (since := "2024-07-28")] abbrev zipWith_distrib_reverse := @reverse_zipWith
+
+@[simp] theorem zipWith_replicate {a : α} {b : β} {m n : Nat} :
+    zipWith f (replicate m a) (replicate n b) = replicate (min m n) (f a b) := by
+  rw [zipWith_eq_zipWith_take_min]
+  simp
+
+/-! ### zip -/
+
+@[simp] theorem length_zip (l₁ : List α) (l₂ : List β) :
+    length (zip l₁ l₂) = min (length l₁) (length l₂) := by
+  simp [zip]
+
+theorem lt_length_left_of_zip {i : Nat} {l : List α} {l' : List β} (h : i < (zip l l').length) :
+    i < l.length :=
+  lt_length_left_of_zipWith h
+
+theorem lt_length_right_of_zip {i : Nat} {l : List α} {l' : List β} (h : i < (zip l l').length) :
+    i < l'.length :=
+  lt_length_right_of_zipWith h
+
+@[simp]
+theorem getElem_zip {l : List α} {l' : List β} {i : Nat} {h : i < (zip l l').length} :
+    (zip l l')[i] =
+      (l[i]'(lt_length_left_of_zip h), l'[i]'(lt_length_right_of_zip h)) :=
+  getElem_zipWith (h := h)
+
+theorem zip_eq_zip_take_min : ∀ (l₁ : List α) (l₂ : List β),
+    zip l₁ l₂ = zip (l₁.take (min l₁.length l₂.length)) (l₂.take (min l₁.length l₂.length))
+  | [], _ => by simp
+  | _, [] => by simp
+  | a :: l₁, b :: l₂ => by simp [succ_min_succ, zip_eq_zip_take_min l₁ l₂]
+
+@[simp] theorem zip_replicate {a : α} {b : β} {m n : Nat} :
+    zip (replicate m a) (replicate n b) = replicate (min m n) (a, b) := by
+  rw [zip_eq_zip_take_min]
+  simp
+
+end List

src/Init/Data/List/Pairwise.lean

@@ -0,0 +1,307 @@
+/-
+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.Sublist
+import Init.Data.List.Attach
+
+/-!
+# Lemmas about `List.Pairwise` and `List.Nodup`.
+-/
+
+namespace List
+
+open Nat
+
+/-! ## Pairwise and Nodup -/
+
+/-! ### Pairwise -/
+
+theorem Pairwise.sublist : l₁ <+ l₂ → l₂.Pairwise R → l₁.Pairwise R
+  | .slnil, h => h
+  | .cons _ s, .cons _ h₂ => h₂.sublist s
+  | .cons₂ _ s, .cons h₁ h₂ => (h₂.sublist s).cons fun _ h => h₁ _ (s.subset h)
+
+theorem Pairwise.imp {α R S} (H : ∀ {a b}, R a b → S a b) :
+    ∀ {l : List α}, l.Pairwise R → l.Pairwise S
+  | _, .nil => .nil
+  | _, .cons h₁ h₂ => .cons (H ∘ h₁ ·) (h₂.imp H)
+
+theorem rel_of_pairwise_cons (p : (a :: l).Pairwise R) : ∀ {a'}, a' ∈ l → R a a' :=
+  (pairwise_cons.1 p).1 _
+
+theorem Pairwise.of_cons (p : (a :: l).Pairwise R) : Pairwise R l :=
+  (pairwise_cons.1 p).2
+
+theorem Pairwise.tail : ∀ {l : List α} (_p : Pairwise R l), Pairwise R l.tail
+  | [], h => h
+  | _ :: _, h => h.of_cons
+
+theorem Pairwise.imp_of_mem {S : α → α → Prop}
+    (H : ∀ {a b}, a ∈ l → b ∈ l → R a b → S a b) (p : Pairwise R l) : Pairwise S l := by
+  induction p with
+  | nil => constructor
+  | @cons a l r _ ih =>
+    constructor
+    · exact fun x h => H (mem_cons_self ..) (mem_cons_of_mem _ h) <| r x h
+    · exact ih fun m m' => H (mem_cons_of_mem _ m) (mem_cons_of_mem _ m')
+
+theorem Pairwise.and (hR : Pairwise R l) (hS : Pairwise S l) :
+    l.Pairwise fun a b => R a b ∧ S a b := by
+  induction hR with
+  | nil => simp only [Pairwise.nil]
+  | cons R1 _ IH =>
+    simp only [Pairwise.nil, pairwise_cons] at hS ⊢
+    exact ⟨fun b bl => ⟨R1 b bl, hS.1 b bl⟩, IH hS.2⟩
+
+theorem pairwise_and_iff : l.Pairwise (fun a b => R a b ∧ S a b) ↔ Pairwise R l ∧ Pairwise S l :=
+  ⟨fun h => ⟨h.imp fun h => h.1, h.imp fun h => h.2⟩, fun ⟨hR, hS⟩ => hR.and hS⟩
+
+theorem Pairwise.imp₂ (H : ∀ a b, R a b → S a b → T a b)
+    (hR : Pairwise R l) (hS : l.Pairwise S) : l.Pairwise T :=
+  (hR.and hS).imp fun ⟨h₁, h₂⟩ => H _ _ h₁ h₂
+
+theorem Pairwise.iff_of_mem {S : α → α → Prop} {l : List α}
+    (H : ∀ {a b}, a ∈ l → b ∈ l → (R a b ↔ S a b)) : Pairwise R l ↔ Pairwise S l :=
+  ⟨Pairwise.imp_of_mem fun m m' => (H m m').1, Pairwise.imp_of_mem fun m m' => (H m m').2⟩
+
+theorem Pairwise.iff {S : α → α → Prop} (H : ∀ a b, R a b ↔ S a b) {l : List α} :
+    Pairwise R l ↔ Pairwise S l :=
+  Pairwise.iff_of_mem fun _ _ => H ..
+
+theorem pairwise_of_forall {l : List α} (H : ∀ x y, R x y) : Pairwise R l := by
+  induction l <;> simp [*]
+
+theorem Pairwise.and_mem {l : List α} :
+    Pairwise R l ↔ Pairwise (fun x y => x ∈ l ∧ y ∈ l ∧ R x y) l :=
+  Pairwise.iff_of_mem <| by simp (config := { contextual := true })
+
+theorem Pairwise.imp_mem {l : List α} :
+    Pairwise R l ↔ Pairwise (fun x y => x ∈ l → y ∈ l → R x y) l :=
+  Pairwise.iff_of_mem <| by simp (config := { contextual := true })
+
+theorem Pairwise.forall_of_forall_of_flip (h₁ : ∀ x ∈ l, R x x) (h₂ : Pairwise R l)
+    (h₃ : l.Pairwise (flip R)) : ∀ ⦃x⦄, x ∈ l → ∀ ⦃y⦄, y ∈ l → R x y := by
+  induction l with
+  | nil => exact forall_mem_nil _
+  | cons a l ih =>
+    rw [pairwise_cons] at h₂ h₃
+    simp only [mem_cons]
+    rintro x (rfl | hx) y (rfl | hy)
+    · exact h₁ _ (l.mem_cons_self _)
+    · exact h₂.1 _ hy
+    · exact h₃.1 _ hx
+    · exact ih (fun x hx => h₁ _ <| mem_cons_of_mem _ hx) h₂.2 h₃.2 hx hy
+
+theorem pairwise_singleton (R) (a : α) : Pairwise R [a] := by simp
+
+theorem pairwise_pair {a b : α} : Pairwise R [a, b] ↔ R a b := by simp
+
+theorem pairwise_map {l : List α} :
+    (l.map f).Pairwise R ↔ l.Pairwise fun a b => R (f a) (f b) := by
+  induction l
+  · simp
+  · simp only [map, pairwise_cons, forall_mem_map, *]
+
+theorem Pairwise.of_map {S : β → β → Prop} (f : α → β) (H : ∀ a b : α, S (f a) (f b) → R a b)
+    (p : Pairwise S (map f l)) : Pairwise R l :=
+  (pairwise_map.1 p).imp (H _ _)
+
+theorem Pairwise.map {S : β → β → Prop} (f : α → β) (H : ∀ a b : α, R a b → S (f a) (f b))
+    (p : Pairwise R l) : Pairwise S (map f l) :=
+  pairwise_map.2 <| p.imp (H _ _)
+
+theorem pairwise_filterMap (f : β → Option α) {l : List β} :
+    Pairwise R (filterMap f l) ↔ Pairwise (fun a a' : β => ∀ b ∈ f a, ∀ b' ∈ f a', R b b') l := by
+  let _S (a a' : β) := ∀ b ∈ f a, ∀ b' ∈ f a', R b b'
+  simp only [Option.mem_def]
+  induction l with
+  | nil => simp only [filterMap, Pairwise.nil]
+  | cons a l IH => ?_
+  match e : f a with
+  | none =>
+    rw [filterMap_cons_none e, pairwise_cons]
+    simp only [e, false_implies, implies_true, true_and, IH]
+  | some b =>
+    rw [filterMap_cons_some e]
+    simpa [IH, e] using fun _ =>
+      ⟨fun h a ha b hab => h _ _ ha hab, fun h a b ha hab => h _ ha _ hab⟩
+
+theorem Pairwise.filterMap {S : β → β → Prop} (f : α → Option β)
+    (H : ∀ a a' : α, R a a' → ∀ b ∈ f a, ∀ b' ∈ f a', S b b') {l : List α} (p : Pairwise R l) :
+    Pairwise S (filterMap f l) :=
+  (pairwise_filterMap _).2 <| p.imp (H _ _)
+
+@[deprecated Pairwise.filterMap (since := "2024-07-29")] abbrev Pairwise.filter_map := @Pairwise.filterMap
+
+theorem pairwise_filter (p : α → Prop) [DecidablePred p] {l : List α} :
+    Pairwise R (filter p l) ↔ Pairwise (fun x y => p x → p y → R x y) l := by
+  rw [← filterMap_eq_filter, pairwise_filterMap]
+  simp
+
+theorem Pairwise.filter (p : α → Bool) : Pairwise R l → Pairwise R (filter p l) :=
+  Pairwise.sublist (filter_sublist _)
+
+theorem pairwise_append {l₁ l₂ : List α} :
+    (l₁ ++ l₂).Pairwise R ↔ l₁.Pairwise R ∧ l₂.Pairwise R ∧ ∀ a ∈ l₁, ∀ b ∈ l₂, R a b := by
+  induction l₁ <;> simp [*, or_imp, forall_and, and_assoc, and_left_comm]
+
+theorem pairwise_append_comm {R : α → α → Prop} (s : ∀ {x y}, R x y → R y x) {l₁ l₂ : List α} :
+    Pairwise R (l₁ ++ l₂) ↔ Pairwise R (l₂ ++ l₁) := by
+  have (l₁ l₂ : List α) (H : ∀ x : α, x ∈ l₁ → ∀ y : α, y ∈ l₂ → R x y)
+    (x : α) (xm : x ∈ l₂) (y : α) (ym : y ∈ l₁) : R x y := s (H y ym x xm)
+  simp only [pairwise_append, and_left_comm]; rw [Iff.intro (this l₁ l₂) (this l₂ l₁)]
+
+theorem pairwise_middle {R : α → α → Prop} (s : ∀ {x y}, R x y → R y x) {a : α} {l₁ l₂ : List α} :
+    Pairwise R (l₁ ++ a :: l₂) ↔ Pairwise R (a :: (l₁ ++ l₂)) := by
+  show Pairwise R (l₁ ++ ([a] ++ l₂)) ↔ Pairwise R ([a] ++ l₁ ++ l₂)
+  rw [← append_assoc, pairwise_append, @pairwise_append _ _ ([a] ++ l₁), pairwise_append_comm s]
+  simp only [mem_append, or_comm]
+
+theorem pairwise_join {L : List (List α)} :
+    Pairwise R (join L) ↔
+      (∀ l ∈ L, Pairwise R l) ∧ Pairwise (fun l₁ l₂ => ∀ x ∈ l₁, ∀ y ∈ l₂, R x y) L := by
+  induction L with
+  | nil => simp
+  | cons l L IH =>
+    simp only [join, pairwise_append, IH, mem_join, exists_imp, and_imp, forall_mem_cons,
+      pairwise_cons, and_assoc, and_congr_right_iff]
+    rw [and_comm, and_congr_left_iff]
+    intros; exact ⟨fun h a b c d e => h c d e a b, fun h c d e a b => h a b c d e⟩
+
+theorem pairwise_bind {R : β → β → Prop} {l : List α} {f : α → List β} :
+    List.Pairwise R (l.bind f) ↔
+      (∀ a ∈ l, Pairwise R (f a)) ∧ Pairwise (fun a₁ a₂ => ∀ x ∈ f a₁, ∀ y ∈ f a₂, R x y) l := by
+  simp [List.bind, pairwise_join, pairwise_map]
+
+theorem pairwise_reverse {l : List α} :
+    l.reverse.Pairwise R ↔ l.Pairwise (fun a b => R b a) := by
+  induction l <;> simp [*, pairwise_append, and_comm]
+
+@[simp] theorem pairwise_replicate {n : Nat} {a : α} :
+    (replicate n a).Pairwise R ↔ n ≤ 1 ∨ R a a := by
+  induction n with
+  | zero => simp
+  | succ n ih =>
+    simp only [replicate_succ, pairwise_cons, mem_replicate, ne_eq, and_imp,
+      forall_eq_apply_imp_iff, ih]
+    constructor
+    · rintro ⟨h, h' | h'⟩
+      · by_cases w : n = 0
+        · left
+          subst w
+          simp
+        · right
+          exact h w
+      · right
+        exact h'
+    · rintro (h | h)
+      · obtain rfl := eq_zero_of_le_zero (le_of_lt_succ h)
+        simp
+      · exact ⟨fun _ => h, Or.inr h⟩
+
+theorem Pairwise.drop {l : List α} {n : Nat} (h : List.Pairwise R l) : List.Pairwise R (l.drop n) :=
+  h.sublist (drop_sublist _ _)
+
+theorem Pairwise.take {l : List α} {n : Nat} (h : List.Pairwise R l) : List.Pairwise R (l.take n) :=
+  h.sublist (take_sublist _ _)
+
+theorem pairwise_iff_forall_sublist : l.Pairwise R ↔ (∀ {a b}, [a,b] <+ l → R a b) := by
+  induction l with
+  | nil => simp
+  | cons hd tl IH =>
+    rw [List.pairwise_cons]
+    constructor <;> intro h
+    · intro
+      | a, b, .cons _ hab => exact IH.mp h.2 hab
+      | _, b, .cons₂ _ hab => refine h.1 _ (hab.subset ?_); simp
+    · constructor
+      · intro x hx
+        apply h
+        rw [List.cons_sublist_cons, List.singleton_sublist]
+        exact hx
+      · apply IH.mpr
+        intro a b hab
+        apply h; exact hab.cons _
+
+theorem Pairwise.rel_of_mem_take_of_mem_drop
+    {l : List α} (h : l.Pairwise R) (hx : x ∈ l.take n) (hy : y ∈ l.drop n) : R x y := by
+  apply pairwise_iff_forall_sublist.mp h
+  rw [← take_append_drop n l, sublist_append_iff]
+  refine ⟨[x], [y], rfl, by simpa, by simpa⟩
+
+theorem Pairwise.rel_of_mem_append
+    {l₁ l₂ : List α} (h : (l₁ ++ l₂).Pairwise R) (hx : x ∈ l₁) (hy : y ∈ l₂) : R x y := by
+  apply pairwise_iff_forall_sublist.mp h
+  rw [sublist_append_iff]
+  exact ⟨[x], [y], rfl, by simpa, by simpa⟩
+
+theorem pairwise_of_forall_mem_list {l : List α} {r : α → α → Prop} (h : ∀ a ∈ l, ∀ b ∈ l, r a b) :
+    l.Pairwise r := by
+  rw [pairwise_iff_forall_sublist]
+  intro a b hab
+  apply h <;> (apply hab.subset; simp)
+
+theorem pairwise_pmap {p : β → Prop} {f : ∀ b, p b → α} {l : List β} (h : ∀ x ∈ l, p x) :
+    Pairwise R (l.pmap f h) ↔
+      Pairwise (fun b₁ b₂ => ∀ (h₁ : p b₁) (h₂ : p b₂), R (f b₁ h₁) (f b₂ h₂)) l := by
+  induction l with
+  | nil => simp
+  | cons a l ihl =>
+    obtain ⟨_, hl⟩ : p a ∧ ∀ b, b ∈ l → p b := by simpa using h
+    simp only [ihl hl, pairwise_cons, exists₂_imp, pmap, and_congr_left_iff, mem_pmap]
+    refine fun _ => ⟨fun H b hb _ hpb => H _ _ hb rfl, ?_⟩
+    rintro H _ b hb rfl
+    exact H b hb _ _
+
+theorem Pairwise.pmap {l : List α} (hl : Pairwise R l) {p : α → Prop} {f : ∀ a, p a → β}
+    (h : ∀ x ∈ l, p x) {S : β → β → Prop}
+    (hS : ∀ ⦃x⦄ (hx : p x) ⦃y⦄ (hy : p y), R x y → S (f x hx) (f y hy)) :
+    Pairwise S (l.pmap f h) := by
+  refine (pairwise_pmap h).2 (Pairwise.imp_of_mem ?_ hl)
+  intros; apply hS; assumption
+
+/-! ### Nodup -/
+
+@[simp]
+theorem nodup_nil : @Nodup α [] :=
+  Pairwise.nil
+
+@[simp]
+theorem nodup_cons {a : α} {l : List α} : Nodup (a :: l) ↔ a ∉ l ∧ Nodup l := by
+  simp only [Nodup, pairwise_cons, forall_mem_ne]
+
+theorem Nodup.sublist : l₁ <+ l₂ → Nodup l₂ → Nodup l₁ :=
+  Pairwise.sublist
+
+theorem Sublist.nodup : l₁ <+ l₂ → Nodup l₂ → Nodup l₁ :=
+  Nodup.sublist
+
+theorem getElem?_inj {xs : List α}
+    (h₀ : i < xs.length) (h₁ : Nodup xs) (h₂ : xs[i]? = xs[j]?) : i = j := by
+  induction xs generalizing i j with
+  | nil => cases h₀
+  | cons x xs ih =>
+    match i, j with
+    | 0, 0 => rfl
+    | i+1, j+1 =>
+      cases h₁ with
+      | cons ha h₁ =>
+        simp only [getElem?_cons_succ] at h₂
+        exact congrArg (· + 1) (ih (Nat.lt_of_succ_lt_succ h₀) h₁ h₂)
+    | i+1, 0 => ?_
+    | 0, j+1 => ?_
+    all_goals
+      simp only [get?_eq_getElem?, getElem?_cons_zero, getElem?_cons_succ] at h₂
+      cases h₁; rename_i h' h
+      have := h x ?_ rfl; cases this
+      rw [mem_iff_get?]
+      simp only [get?_eq_getElem?]
+    exact ⟨_, h₂⟩; exact ⟨_ , h₂.symm⟩
+
+@[simp] theorem nodup_replicate {n : Nat} {a : α} :
+    (replicate n a).Nodup ↔ n ≤ 1 := by simp [Nodup]
+
+end List

src/Init/Data/List/Perm.lean

@@ -0,0 +1,465 @@
+/-
+Copyright (c) 2015 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.List.Pairwise
+import Init.Data.List.Erase
+
+/-!
+# List Permutations
+
+This file introduces the `List.Perm` relation, which is true if two lists are permutations of one
+another.
+
+## Notation
+
+The notation `~` is used for permutation equivalence.
+-/
+
+open Nat
+
+namespace List
+
+open Perm (swap)
+
+@[simp, refl] protected theorem Perm.refl : ∀ l : List α, l ~ l
+  | [] => .nil
+  | x :: xs => (Perm.refl xs).cons x
+
+protected theorem Perm.rfl {l : List α} : l ~ l := .refl _
+
+theorem Perm.of_eq (h : l₁ = l₂) : l₁ ~ l₂ := h ▸ .rfl
+
+protected theorem Perm.symm {l₁ l₂ : List α} (h : l₁ ~ l₂) : l₂ ~ l₁ := by
+  induction h with
+  | nil => exact nil
+  | cons _ _ ih => exact cons _ ih
+  | swap => exact swap ..
+  | trans _ _ ih₁ ih₂ => exact trans ih₂ ih₁
+
+theorem perm_comm {l₁ l₂ : List α} : l₁ ~ l₂ ↔ l₂ ~ l₁ := ⟨Perm.symm, Perm.symm⟩
+
+theorem Perm.swap' (x y : α) {l₁ l₂ : List α} (p : l₁ ~ l₂) : y :: x :: l₁ ~ x :: y :: l₂ :=
+  (swap ..).trans <| p.cons _ |>.cons _
+
+/--
+Similar to `Perm.recOn`, but the `swap` case is generalized to `Perm.swap'`,
+where the tail of the lists are not necessarily the same.
+-/
+@[elab_as_elim] theorem Perm.recOnSwap'
+    {motive : (l₁ : List α) → (l₂ : List α) → l₁ ~ l₂ → Prop} {l₁ l₂ : List α} (p : l₁ ~ l₂)
+    (nil : motive [] [] .nil)
+    (cons : ∀ x {l₁ l₂}, (h : l₁ ~ l₂) → motive l₁ l₂ h → motive (x :: l₁) (x :: l₂) (.cons x h))
+    (swap' : ∀ x y {l₁ l₂}, (h : l₁ ~ l₂) → motive l₁ l₂ h →
+      motive (y :: x :: l₁) (x :: y :: l₂) (.swap' _ _ h))
+    (trans : ∀ {l₁ l₂ l₃}, (h₁ : l₁ ~ l₂) → (h₂ : l₂ ~ l₃) → motive l₁ l₂ h₁ → motive l₂ l₃ h₂ →
+      motive l₁ l₃ (.trans h₁ h₂)) : motive l₁ l₂ p :=
+  have motive_refl l : motive l l (.refl l) :=
+    List.recOn l nil fun x xs ih => cons x (.refl xs) ih
+  Perm.recOn p nil cons (fun x y l => swap' x y (.refl l) (motive_refl l)) trans
+
+theorem Perm.eqv (α) : Equivalence (@Perm α) := ⟨.refl, .symm, .trans⟩
+
+instance isSetoid (α) : Setoid (List α) := .mk Perm (Perm.eqv α)
+
+theorem Perm.mem_iff {a : α} {l₁ l₂ : List α} (p : l₁ ~ l₂) : a ∈ l₁ ↔ a ∈ l₂ := by
+  induction p with
+  | nil => rfl
+  | cons _ _ ih => simp only [mem_cons, ih]
+  | swap => simp only [mem_cons, or_left_comm]
+  | trans _ _ ih₁ ih₂ => simp only [ih₁, ih₂]
+
+theorem Perm.subset {l₁ l₂ : List α} (p : l₁ ~ l₂) : l₁ ⊆ l₂ := fun _ => p.mem_iff.mp
+
+theorem Perm.append_right {l₁ l₂ : List α} (t₁ : List α) (p : l₁ ~ l₂) : l₁ ++ t₁ ~ l₂ ++ t₁ := by
+  induction p with
+  | nil => rfl
+  | cons _ _ ih => exact cons _ ih
+  | swap => exact swap ..
+  | trans _ _ ih₁ ih₂ => exact trans ih₁ ih₂
+
+theorem Perm.append_left {t₁ t₂ : List α} : ∀ l : List α, t₁ ~ t₂ → l ++ t₁ ~ l ++ t₂
+  | [], p => p
+  | x :: xs, p => (p.append_left xs).cons x
+
+theorem Perm.append {l₁ l₂ t₁ t₂ : List α} (p₁ : l₁ ~ l₂) (p₂ : t₁ ~ t₂) : l₁ ++ t₁ ~ l₂ ++ t₂ :=
+  (p₁.append_right t₁).trans (p₂.append_left l₂)
+
+theorem Perm.append_cons (a : α) {h₁ h₂ t₁ t₂ : List α} (p₁ : h₁ ~ h₂) (p₂ : t₁ ~ t₂) :
+    h₁ ++ a :: t₁ ~ h₂ ++ a :: t₂ := p₁.append (p₂.cons a)
+
+@[simp] theorem perm_middle {a : α} : ∀ {l₁ l₂ : List α}, l₁ ++ a :: l₂ ~ a :: (l₁ ++ l₂)
+  | [], _ => .refl _
+  | b :: _, _ => (Perm.cons _ perm_middle).trans (swap a b _)
+
+@[simp] theorem perm_append_singleton (a : α) (l : List α) : l ++ [a] ~ a :: l :=
+  perm_middle.trans <| by rw [append_nil]
+
+theorem perm_append_comm : ∀ {l₁ l₂ : List α}, l₁ ++ l₂ ~ l₂ ++ l₁
+  | [], l₂ => by simp
+  | a :: t, l₂ => (perm_append_comm.cons _).trans perm_middle.symm
+
+theorem perm_append_comm_assoc (l₁ l₂ l₃ : List α) :
+    Perm (l₁ ++ (l₂ ++ l₃)) (l₂ ++ (l₁ ++ l₃)) := by
+  simpa only [List.append_assoc] using perm_append_comm.append_right _
+
+theorem concat_perm (l : List α) (a : α) : concat l a ~ a :: l := by simp
+
+theorem Perm.length_eq {l₁ l₂ : List α} (p : l₁ ~ l₂) : length l₁ = length l₂ := by
+  induction p with
+  | nil => rfl
+  | cons _ _ ih => simp only [length_cons, ih]
+  | swap => rfl
+  | trans _ _ ih₁ ih₂ => simp only [ih₁, ih₂]
+
+theorem Perm.eq_nil {l : List α} (p : l ~ []) : l = [] := eq_nil_of_length_eq_zero p.length_eq
+
+theorem Perm.nil_eq {l : List α} (p : [] ~ l) : [] = l := p.symm.eq_nil.symm
+
+@[simp] theorem perm_nil {l₁ : List α} : l₁ ~ [] ↔ l₁ = [] :=
+  ⟨fun p => p.eq_nil, fun e => e ▸ .rfl⟩
+
+@[simp] theorem nil_perm {l₁ : List α} : [] ~ l₁ ↔ l₁ = [] := perm_comm.trans perm_nil
+
+@[simp]
+theorem not_perm_nil_cons (x : α) (l : List α) : ¬[] ~ x :: l := (nomatch ·.symm.eq_nil)
+
+@[simp]
+theorem not_perm_cons_nil {l : List α} {a : α} : ¬(Perm (a::l) []) :=
+  fun h => by simpa using h.length_eq
+
+theorem Perm.isEmpty_eq {l l' : List α} (h : Perm l l') : l.isEmpty = l'.isEmpty := by
+  cases l <;> cases l' <;> simp_all
+
+@[simp] theorem reverse_perm : ∀ l : List α, reverse l ~ l
+  | [] => .nil
+  | a :: l => reverse_cons .. ▸ (perm_append_singleton _ _).trans ((reverse_perm l).cons a)
+
+theorem perm_cons_append_cons {l l₁ l₂ : List α} (a : α) (p : l ~ l₁ ++ l₂) :
+    a :: l ~ l₁ ++ a :: l₂ := (p.cons a).trans perm_middle.symm
+
+@[simp] theorem perm_replicate {n : Nat} {a : α} {l : List α} :
+    l ~ replicate n a ↔ l = replicate n a := by
+  refine ⟨fun p => eq_replicate.2 ?_, fun h => h ▸ .rfl⟩
+  exact ⟨p.length_eq.trans <| length_replicate .., fun _b m => eq_of_mem_replicate <| p.subset m⟩
+
+@[simp] theorem replicate_perm {n : Nat} {a : α} {l : List α} :
+    replicate n a ~ l ↔ replicate n a = l := (perm_comm.trans perm_replicate).trans eq_comm
+
+@[simp] theorem perm_singleton {a : α} {l : List α} : l ~ [a] ↔ l = [a] := perm_replicate (n := 1)
+
+@[simp] theorem singleton_perm {a : α} {l : List α} : [a] ~ l ↔ [a] = l := replicate_perm (n := 1)
+
+theorem Perm.eq_singleton (h : l ~ [a]) : l = [a] := perm_singleton.mp h
+theorem Perm.singleton_eq (h : [a] ~ l) : [a] = l := singleton_perm.mp h
+
+theorem singleton_perm_singleton {a b : α} : [a] ~ [b] ↔ a = b := by simp
+
+theorem perm_cons_erase [DecidableEq α] {a : α} {l : List α} (h : a ∈ l) : l ~ a :: l.erase a :=
+  let ⟨_l₁, _l₂, _, e₁, e₂⟩ := exists_erase_eq h
+  e₂ ▸ e₁ ▸ perm_middle
+
+theorem Perm.filterMap (f : α → Option β) {l₁ l₂ : List α} (p : l₁ ~ l₂) :
+    filterMap f l₁ ~ filterMap f l₂ := by
+  induction p with
+  | nil => simp
+  | cons x _p IH => cases h : f x <;> simp [h, filterMap_cons, IH, Perm.cons]
+  | swap x y l₂ => cases hx : f x <;> cases hy : f y <;> simp [hx, hy, filterMap_cons, swap]
+  | trans _p₁ _p₂ IH₁ IH₂ => exact IH₁.trans IH₂
+
+theorem Perm.map (f : α → β) {l₁ l₂ : List α} (p : l₁ ~ l₂) : map f l₁ ~ map f l₂ :=
+  filterMap_eq_map f ▸ p.filterMap _
+
+theorem Perm.pmap {p : α → Prop} (f : ∀ a, p a → β) {l₁ l₂ : List α} (p : l₁ ~ l₂) {H₁ H₂} :
+    pmap f l₁ H₁ ~ pmap f l₂ H₂ := by
+  induction p with
+  | nil => simp
+  | cons x _p IH => simp [IH, Perm.cons]
+  | swap x y => simp [swap]
+  | trans _p₁ p₂ IH₁ IH₂ => exact IH₁.trans (IH₂ (H₁ := fun a m => H₂ a (p₂.subset m)))
+
+theorem Perm.filter (p : α → Bool) {l₁ l₂ : List α} (s : l₁ ~ l₂) :
+    filter p l₁ ~ filter p l₂ := by rw [← filterMap_eq_filter]; apply s.filterMap
+
+theorem filter_append_perm (p : α → Bool) (l : List α) :
+    filter p l ++ filter (fun x => !p x) l ~ l := by
+  induction l with
+  | nil => rfl
+  | cons x l ih =>
+    by_cases h : p x <;> simp [h]
+    · exact ih.cons x
+    · exact Perm.trans (perm_append_comm.trans (perm_append_comm.cons _)) (ih.cons x)
+
+theorem exists_perm_sublist {l₁ l₂ l₂' : List α} (s : l₁ <+ l₂) (p : l₂ ~ l₂') :
+    ∃ l₁', l₁' ~ l₁ ∧ l₁' <+ l₂' := by
+  induction p generalizing l₁ with
+  | nil => exact ⟨[], sublist_nil.mp s ▸ .rfl, nil_sublist _⟩
+  | cons x _ IH =>
+    match s with
+    | .cons _ s => let ⟨l₁', p', s'⟩ := IH s; exact ⟨l₁', p', s'.cons _⟩
+    | .cons₂ _ s => let ⟨l₁', p', s'⟩ := IH s; exact ⟨x :: l₁', p'.cons x, s'.cons₂ _⟩
+  | swap x y l' =>
+    match s with
+    | .cons _ (.cons _ s) => exact ⟨_, .rfl, (s.cons _).cons _⟩
+    | .cons _ (.cons₂ _ s) => exact ⟨x :: _, .rfl, (s.cons _).cons₂ _⟩
+    | .cons₂ _ (.cons _ s) => exact ⟨y :: _, .rfl, (s.cons₂ _).cons _⟩
+    | .cons₂ _ (.cons₂ _ s) => exact ⟨x :: y :: _, .swap .., (s.cons₂ _).cons₂ _⟩
+  | trans _ _ IH₁ IH₂ =>
+    let ⟨m₁, pm, sm⟩ := IH₁ s
+    let ⟨r₁, pr, sr⟩ := IH₂ sm
+    exact ⟨r₁, pr.trans pm, sr⟩
+
+theorem Perm.sizeOf_eq_sizeOf [SizeOf α] {l₁ l₂ : List α} (h : l₁ ~ l₂) :
+    sizeOf l₁ = sizeOf l₂ := by
+  induction h with
+  | nil => rfl
+  | cons _ _ h_sz₁₂ => simp [h_sz₁₂]
+  | swap => simp [Nat.add_left_comm]
+  | trans _ _ h_sz₁₂ h_sz₂₃ => simp [h_sz₁₂, h_sz₂₃]
+
+theorem Sublist.exists_perm_append {l₁ l₂ : List α} : l₁ <+ l₂ → ∃ l, l₂ ~ l₁ ++ l
+  | Sublist.slnil => ⟨nil, .rfl⟩
+  | Sublist.cons a s =>
+    let ⟨l, p⟩ := Sublist.exists_perm_append s
+    ⟨a :: l, (p.cons a).trans perm_middle.symm⟩
+  | Sublist.cons₂ a s =>
+    let ⟨l, p⟩ := Sublist.exists_perm_append s
+    ⟨l, p.cons a⟩
+
+theorem Perm.countP_eq (p : α → Bool) {l₁ l₂ : List α} (s : l₁ ~ l₂) :
+    countP p l₁ = countP p l₂ := by
+  simp only [countP_eq_length_filter]
+  exact (s.filter _).length_eq
+
+theorem Perm.countP_congr {l₁ l₂ : List α} (s : l₁ ~ l₂) {p p' : α → Bool}
+    (hp : ∀ x ∈ l₁, p x = p' x) : l₁.countP p = l₂.countP p' := by
+  rw [← s.countP_eq p']
+  clear s
+  induction l₁ with
+  | nil => rfl
+  | cons y s hs =>
+    simp only [mem_cons, forall_eq_or_imp] at hp
+    simp only [countP_cons, hs hp.2, hp.1]
+
+theorem countP_eq_countP_filter_add (l : List α) (p q : α → Bool) :
+    l.countP p = (l.filter q).countP p + (l.filter fun a => !q a).countP p :=
+  countP_append .. ▸ Perm.countP_eq _ (filter_append_perm _ _).symm
+
+theorem Perm.count_eq [DecidableEq α] {l₁ l₂ : List α} (p : l₁ ~ l₂) (a) :
+    count a l₁ = count a l₂ := p.countP_eq _
+
+theorem Perm.foldl_eq' {f : β → α → β} {l₁ l₂ : List α} (p : l₁ ~ l₂)
+    (comm : ∀ x ∈ l₁, ∀ y ∈ l₁, ∀ (z), f (f z x) y = f (f z y) x)
+    (init) : foldl f init l₁ = foldl f init l₂ := by
+  induction p using recOnSwap' generalizing init with
+  | nil => simp
+  | cons x _p IH =>
+    simp only [foldl]
+    apply IH; intros; apply comm <;> exact .tail _ ‹_›
+  | swap' x y _p IH =>
+    simp only [foldl]
+    rw [comm x (.tail _ <| .head _) y (.head _)]
+    apply IH; intros; apply comm <;> exact .tail _ (.tail _ ‹_›)
+  | trans p₁ _p₂ IH₁ IH₂ =>
+    refine (IH₁ comm init).trans (IH₂ ?_ _)
+    intros; apply comm <;> apply p₁.symm.subset <;> assumption
+
+theorem Perm.rec_heq {β : List α → Sort _} {f : ∀ a l, β l → β (a :: l)} {b : β []} {l l' : List α}
+    (hl : l ~ l') (f_congr : ∀ {a l l' b b'}, l ~ l' → HEq b b' → HEq (f a l b) (f a l' b'))
+    (f_swap : ∀ {a a' l b}, HEq (f a (a' :: l) (f a' l b)) (f a' (a :: l) (f a l b))) :
+    HEq (@List.rec α β b f l) (@List.rec α β b f l') := by
+  induction hl with
+  | nil => rfl
+  | cons a h ih => exact f_congr h ih
+  | swap a a' l => exact f_swap
+  | trans _h₁ _h₂ ih₁ ih₂ => exact ih₁.trans ih₂
+
+/-- Lemma used to destruct perms element by element. -/
+theorem perm_inv_core {a : α} {l₁ l₂ r₁ r₂ : List α} :
+    l₁ ++ a :: r₁ ~ l₂ ++ a :: r₂ → l₁ ++ r₁ ~ l₂ ++ r₂ := by
+  -- Necessary generalization for `induction`
+  suffices ∀ s₁ s₂ (_ : s₁ ~ s₂) {l₁ l₂ r₁ r₂},
+      l₁ ++ a :: r₁ = s₁ → l₂ ++ a :: r₂ = s₂ → l₁ ++ r₁ ~ l₂ ++ r₂ from (this _ _ · rfl rfl)
+  intro s₁ s₂ p
+  induction p using Perm.recOnSwap' with intro l₁ l₂ r₁ r₂ e₁ e₂
+  | nil =>
+    simp at e₁
+  | cons x p IH =>
+    cases l₁ <;> cases l₂ <;>
+      dsimp at e₁ e₂ <;> injections <;> subst_vars
+    · exact p
+    · exact p.trans perm_middle
+    · exact perm_middle.symm.trans p
+    · exact (IH rfl rfl).cons _
+  | swap' x y p IH =>
+    obtain _ | ⟨y, _ | ⟨z, l₁⟩⟩ := l₁
+      <;> obtain _ | ⟨u, _ | ⟨v, l₂⟩⟩ := l₂
+      <;> dsimp at e₁ e₂ <;> injections <;> subst_vars
+      <;> try exact p.cons _
+    · exact (p.trans perm_middle).cons u
+    · exact ((p.trans perm_middle).cons _).trans (swap _ _ _)
+    · exact (perm_middle.symm.trans p).cons y
+    · exact (swap _ _ _).trans ((perm_middle.symm.trans p).cons u)
+    · exact (IH rfl rfl).swap' _ _
+  | trans p₁ p₂ IH₁ IH₂ =>
+    subst e₁ e₂
+    obtain ⟨l₂, r₂, rfl⟩ := append_of_mem (a := a) (p₁.subset (by simp))
+    exact (IH₁ rfl rfl).trans (IH₂ rfl rfl)
+
+theorem Perm.cons_inv {a : α} {l₁ l₂ : List α} : a :: l₁ ~ a :: l₂ → l₁ ~ l₂ :=
+  perm_inv_core (l₁ := []) (l₂ := [])
+
+@[simp] theorem perm_cons (a : α) {l₁ l₂ : List α} : a :: l₁ ~ a :: l₂ ↔ l₁ ~ l₂ :=
+  ⟨.cons_inv, .cons a⟩
+
+theorem perm_append_left_iff {l₁ l₂ : List α} : ∀ l, l ++ l₁ ~ l ++ l₂ ↔ l₁ ~ l₂
+  | [] => .rfl
+  | a :: l => (perm_cons a).trans (perm_append_left_iff l)
+
+theorem perm_append_right_iff {l₁ l₂ : List α} (l) : l₁ ++ l ~ l₂ ++ l ↔ l₁ ~ l₂ := by
+  refine ⟨fun p => ?_, .append_right _⟩
+  exact (perm_append_left_iff _).1 <| perm_append_comm.trans <| p.trans perm_append_comm
+
+section DecidableEq
+
+variable [DecidableEq α]
+
+theorem Perm.erase (a : α) {l₁ l₂ : List α} (p : l₁ ~ l₂) : l₁.erase a ~ l₂.erase a :=
+  if h₁ : a ∈ l₁ then
+    have h₂ : a ∈ l₂ := p.subset h₁
+    .cons_inv <| (perm_cons_erase h₁).symm.trans <| p.trans (perm_cons_erase h₂)
+  else by
+    have h₂ : a ∉ l₂ := mt p.mem_iff.2 h₁
+    rw [erase_of_not_mem h₁, erase_of_not_mem h₂]; exact p
+
+theorem cons_perm_iff_perm_erase {a : α} {l₁ l₂ : List α} :
+    a :: l₁ ~ l₂ ↔ a ∈ l₂ ∧ l₁ ~ l₂.erase a := by
+  refine ⟨fun h => ?_, fun ⟨m, h⟩ => (h.cons a).trans (perm_cons_erase m).symm⟩
+  have : a ∈ l₂ := h.subset (mem_cons_self a l₁)
+  exact ⟨this, (h.trans <| perm_cons_erase this).cons_inv⟩
+
+theorem perm_iff_count {l₁ l₂ : List α} : l₁ ~ l₂ ↔ ∀ a, count a l₁ = count a l₂ := by
+  refine ⟨Perm.count_eq, fun H => ?_⟩
+  induction l₁ generalizing l₂ with
+  | nil =>
+    match l₂ with
+    | nil => rfl
+    | cons b l₂ =>
+      specialize H b
+      simp at H
+  | cons a l₁ IH =>
+    have : a ∈ l₂ := count_pos_iff_mem.mp (by rw [← H]; simp)
+    refine ((IH fun b => ?_).cons a).trans (perm_cons_erase this).symm
+    specialize H b
+    rw [(perm_cons_erase this).count_eq] at H
+    by_cases h : b = a <;> simpa [h, count_cons, Nat.succ_inj'] using H
+
+theorem isPerm_iff : ∀ {l₁ l₂ : List α}, l₁.isPerm l₂ ↔ l₁ ~ l₂
+  | [], [] => by simp [isPerm, isEmpty]
+  | [], _ :: _ => by simp [isPerm, isEmpty, Perm.nil_eq]
+  | a :: l₁, l₂ => by simp [isPerm, isPerm_iff, cons_perm_iff_perm_erase]
+
+instance decidablePerm (l₁ l₂ : List α) : Decidable (l₁ ~ l₂) := decidable_of_iff _ isPerm_iff
+
+protected theorem Perm.insert (a : α) {l₁ l₂ : List α} (p : l₁ ~ l₂) :
+    l₁.insert a ~ l₂.insert a := by
+  if h : a ∈ l₁ then
+    simp [h, p.subset h, p]
+  else
+    have := p.cons a
+    simpa [h, mt p.mem_iff.2 h] using this
+
+theorem perm_insert_swap (x y : α) (l : List α) :
+    List.insert x (List.insert y l) ~ List.insert y (List.insert x l) := by
+  by_cases xl : x ∈ l <;> by_cases yl : y ∈ l <;> simp [xl, yl]
+  if xy : x = y then simp [xy] else
+  simp [List.insert, xl, yl, xy, Ne.symm xy]
+  constructor
+
+end DecidableEq
+
+theorem Perm.pairwise_iff {R : α → α → Prop} (S : ∀ {x y}, R x y → R y x) :
+    ∀ {l₁ l₂ : List α} (_p : l₁ ~ l₂), Pairwise R l₁ ↔ Pairwise R l₂ :=
+  suffices ∀ {l₁ l₂}, l₁ ~ l₂ → Pairwise R l₁ → Pairwise R l₂
+    from fun p => ⟨this p, this p.symm⟩
+  fun {l₁ l₂} p d => by
+    induction d generalizing l₂ with
+    | nil => rw [← p.nil_eq]; constructor
+    | cons h _ IH =>
+      have : _ ∈ l₂ := p.subset (mem_cons_self _ _)
+      obtain ⟨s₂, t₂, rfl⟩ := append_of_mem this
+      have p' := (p.trans perm_middle).cons_inv
+      refine (pairwise_middle S).2 (pairwise_cons.2 ⟨fun b m => ?_, IH p'⟩)
+      exact h _ (p'.symm.subset m)
+
+theorem Pairwise.perm {R : α → α → Prop} {l l' : List α} (hR : l.Pairwise R) (hl : l ~ l')
+    (hsymm : ∀ {x y}, R x y → R y x) : l'.Pairwise R := (hl.pairwise_iff hsymm).mp hR
+
+theorem Perm.pairwise {R : α → α → Prop} {l l' : List α} (hl : l ~ l') (hR : l.Pairwise R)
+    (hsymm : ∀ {x y}, R x y → R y x) : l'.Pairwise R := hR.perm hl hsymm
+
+/--
+If two lists are sorted by an antisymmetric relation, and permutations of each other,
+they must be equal.
+-/
+theorem Perm.eq_of_sorted : ∀ {l₁ l₂ : List α}
+    (_ : ∀ a b, a ∈ l₁ → b ∈ l₂ → le a b → le b a → a = b)
+    (_ : l₁.Pairwise le) (_ : l₂.Pairwise le) (_ : l₁ ~ l₂), l₁ = l₂
+  | [], [], _, _, _, _ => rfl
+  | [], b :: l₂, _, _, _, h => by simp_all
+  | a :: l₁, [], _, _, _, h => by simp_all
+  | a :: l₁, b :: l₂, w, h₁, h₂, h => by
+    have am : a ∈ b :: l₂ := h.subset (mem_cons_self _ _)
+    have bm : b ∈ a :: l₁ := h.symm.subset (mem_cons_self _ _)
+    have ab : a = b := by
+      simp only [mem_cons] at am
+      rcases am with rfl | am
+      · rfl
+      · simp only [mem_cons] at bm
+        rcases bm with rfl | bm
+        · rfl
+        · exact w _ _ (mem_cons_self _ _) (mem_cons_self _ _)
+            (rel_of_pairwise_cons h₁ bm) (rel_of_pairwise_cons h₂ am)
+    subst ab
+    simp only [perm_cons] at h
+    have := Perm.eq_of_sorted
+      (fun x y hx hy => w x y (mem_cons_of_mem a hx) (mem_cons_of_mem a hy))
+      h₁.tail h₂.tail h
+    simp_all
+
+theorem Nodup.perm {l l' : List α} (hR : l.Nodup) (hl : l ~ l') : l'.Nodup :=
+  Pairwise.perm hR hl (by intro x y h h'; simp_all)
+
+theorem Perm.nodup {l l' : List α} (hl : l ~ l') (hR : l.Nodup) : l'.Nodup := hR.perm hl
+
+theorem Perm.nodup_iff {l₁ l₂ : List α} : l₁ ~ l₂ → (Nodup l₁ ↔ Nodup l₂) :=
+  Perm.pairwise_iff <| @Ne.symm α
+
+theorem Perm.join {l₁ l₂ : List (List α)} (h : l₁ ~ l₂) : l₁.join ~ l₂.join := by
+  induction h with
+  | nil => rfl
+  | cons _ _ ih => simp only [join_cons, perm_append_left_iff, ih]
+  | swap => simp only [join_cons, ← append_assoc, perm_append_right_iff]; exact perm_append_comm ..
+  | trans _ _ ih₁ ih₂ => exact trans ih₁ ih₂
+
+theorem Perm.bind_right {l₁ l₂ : List α} (f : α → List β) (p : l₁ ~ l₂) : l₁.bind f ~ l₂.bind f :=
+  (p.map _).join
+
+theorem Perm.eraseP (f : α → Bool) {l₁ l₂ : List α}
+    (H : Pairwise (fun a b => f a → f b → False) l₁) (p : l₁ ~ l₂) : eraseP f l₁ ~ eraseP f l₂ := by
+  induction p with
+  | nil => simp
+  | cons a p IH =>
+    if h : f a then simp [h, p]
+    else simp [h]; exact IH (pairwise_cons.1 H).2
+  | swap a b l =>
+    by_cases h₁ : f a <;> by_cases h₂ : f b <;> simp [h₁, h₂]
+    · cases (pairwise_cons.1 H).1 _ (mem_cons.2 (Or.inl rfl)) h₂ h₁
+    · apply swap
+  | trans p₁ _ IH₁ IH₂ =>
+    refine (IH₁ H).trans (IH₂ ((p₁.pairwise_iff ?_).1 H))
+    exact fun h h₁ h₂ => h h₂ h₁
+
+end List

src/Init/Data/List/Range.lean

@@ -0,0 +1,57 @@
+/-
+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.Pairwise
+
+/-!
+# Lemmas about `List.range` and `List.enum`
+
+Most of the results are deferred to `Data.Init.List.Nat.Range`, where more results about
+natural arithmetic are available.
+-/
+
+namespace List
+
+open Nat
+
+/-! ## Ranges and enumeration -/
+
+/-! ### enumFrom -/
+
+@[simp]
+theorem enumFrom_eq_nil {n : Nat} {l : List α} : List.enumFrom n l = [] ↔ l = [] := by
+  cases l <;> simp
+
+@[simp] theorem enumFrom_length : ∀ {n} {l : List α}, (enumFrom n l).length = l.length
+  | _, [] => rfl
+  | _, _ :: _ => congrArg Nat.succ enumFrom_length
+
+@[simp]
+theorem getElem?_enumFrom :
+    ∀ n (l : List α) m, (enumFrom n l)[m]? = l[m]?.map fun a => (n + m, a)
+  | n, [], m => rfl
+  | n, a :: l, 0 => by simp
+  | n, a :: l, m + 1 => by
+    simp only [enumFrom_cons, getElem?_cons_succ]
+    exact (getElem?_enumFrom (n + 1) l m).trans <| by rw [Nat.add_right_comm]; rfl
+
+@[simp]
+theorem getElem_enumFrom (l : List α) (n) (i : Nat) (h : i < (l.enumFrom n).length) :
+    (l.enumFrom n)[i] = (n + i, l[i]'(by simpa [enumFrom_length] using h)) := by
+  simp only [enumFrom_length] at h
+  rw [getElem_eq_getElem?]
+  simp only [getElem?_enumFrom, getElem?_eq_getElem h]
+  simp
+
+theorem map_fst_add_enumFrom_eq_enumFrom (l : List α) (n k : Nat) :
+    map (Prod.map (· + n) id) (enumFrom k l) = enumFrom (n + k) l :=
+  ext_getElem? fun i ↦ by simp [(· ∘ ·), Nat.add_comm, Nat.add_left_comm]; rfl
+
+theorem map_fst_add_enum_eq_enumFrom (l : List α) (n : Nat) :
+    map (Prod.map (· + n) id) (enum l) = enumFrom n l :=
+  map_fst_add_enumFrom_eq_enumFrom l _ _
+
+end List

src/Init/Data/List/Sort.lean

@@ -0,0 +1,9 @@
+/-
+Copyright (c) 2024 Lean FRO. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Kim Morrison
+-/
+prelude
+import Init.Data.List.Sort.Basic
+import Init.Data.List.Sort.Impl
+import Init.Data.List.Sort.Lemmas

src/Init/Data/List/Sort/Basic.lean

@@ -0,0 +1,81 @@
+/-
+Copyright (c) 2024 Lean FRO. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Kim Morrison
+-/
+prelude
+import Init.Data.List.Impl
+
+/-!
+# Definition of `merge` and `mergeSort`.
+
+These definitions are intended for verification purposes,
+and are replaced at runtime by efficient versions in `Init.Data.List.Sort.Impl`.
+-/
+
+namespace List
+
+/--
+`O(min |l| |r|)`. Merge two lists using `le` as a switch.
+
+This version is not tail-recursive,
+but it is replaced at runtime by `mergeTR` using a `@[csimp]` lemma.
+-/
+def merge (le : α → α → Bool) : List α → List α → List α
+  | [], ys => ys
+  | xs, [] => xs
+  | x :: xs, y :: ys =>
+    if le x y then
+      x :: merge le xs (y :: ys)
+    else
+      y :: merge le (x :: xs) ys
+
+@[simp] theorem merge_nil_left (ys : List α) : merge le [] ys = ys := by simp [merge]
+@[simp] theorem merge_nil_right (xs : List α) : merge le xs [] = xs := by
+  induction xs with
+  | nil => simp [merge]
+  | cons x xs ih => simp [merge, ih]
+
+/--
+Split a list in two equal parts. If the length is odd, the first part will be one element longer.
+-/
+def splitInTwo (l : { l : List α // l.length = n }) :
+    { l : List α // l.length = (n+1)/2 } × { l : List α // l.length = n/2 } :=
+  let r := splitAt ((n+1)/2) l.1
+  (⟨r.1, by simp [r, splitAt_eq, l.2]; omega⟩, ⟨r.2, by simp [r, splitAt_eq, l.2]; omega⟩)
+
+/--
+Simplified implementation of stable merge sort.
+
+This function is designed for reasoning about the algorithm, and is not efficient.
+(It particular it uses the non tail-recursive `merge` function,
+and so can not be run on large lists, but also makes unnecessary traversals of lists.)
+It is replaced at runtime in the compiler by `mergeSortTR₂` using a `@[csimp]` lemma.
+
+Because we want the sort to be stable,
+it is essential that we split the list in two contiguous sublists.
+-/
+def mergeSort (le : α → α → Bool) : List α → List α
+  | [] => []
+  | [a] => [a]
+  | a :: b :: xs =>
+    let lr := splitInTwo ⟨a :: b :: xs, rfl⟩
+    have := by simpa using lr.2.2
+    have := by simpa using lr.1.2
+    merge le (mergeSort le lr.1) (mergeSort le lr.2)
+termination_by l => l.length
+
+
+/--
+Given an ordering relation `le : α → α → Bool`,
+construct the reverse lexicographic ordering on `Nat × α`.
+which first compares the second components using `le`,
+but if these are equivalent (in the sense `le a.2 b.2 && le b.2 a.2`)
+then compares the first components using `≤`.
+
+This function is only used in stating the stability properties of `mergeSort`.
+-/
+def enumLE (le : α → α → Bool) (a b : Nat × α) : Bool :=
+  if le a.2 b.2 then if le b.2 a.2 then a.1 ≤ b.1 else true else false
+
+end List

src/Init/Data/List/Sort/Impl.lean

@@ -0,0 +1,237 @@
+/-
+Copyright (c) 2024 Lean FRO. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Kim Morrison
+-/
+prelude
+import Init.Data.List.Sort.Lemmas
+
+/-!
+# Replacing `merge` and `mergeSort` at runtime with tail-recursive and faster versions.
+
+We replace `merge` with `mergeTR` using a `@[csimp]` lemma.
+
+We replace `mergeSort` in two steps:
+* first with `mergeSortTR`, which while not tail-recursive itself (it can't be),
+  uses `mergeTR` internally.
+* second with `mergeSortTR₂`, which achieves an ~20% speed-up over `mergeSortTR`
+  by avoiding some unnecessary list reversals.
+
+There is no public API in this file; it solely exists to implement the `@[csimp]` lemmas
+affecting runtime behaviour.
+
+## Future work
+The current runtime implementation could be further improved in a number of ways, e.g.:
+* only walking the list once during splitting,
+* using insertion sort for small chunks rather than splitting all the way down to singletons,
+* identifying already sorted or reverse sorted chunks and skipping them.
+
+Because the theory developed for `mergeSort` is independent of the runtime implementation,
+as long as such improvements are carefully validated by benchmarking,
+they can be done without changing the theory, as long as a `@[csimp]` lemma is provided.
+-/
+
+open List
+
+namespace List.MergeSort.Internal
+
+/--
+`O(min |l| |r|)`. Merge two lists using `le` as a switch.
+-/
+def mergeTR (le : α → α → Bool) (l₁ l₂ : List α) : List α :=
+  go l₁ l₂ []
+where go : List α → List α → List α → List α
+  | [], l₂, acc => reverseAux acc l₂
+  | l₁, [], acc => reverseAux acc l₁
+  | x :: xs, y :: ys, acc =>
+    if le x y then
+      go xs (y :: ys) (x :: acc)
+    else
+      go (x :: xs) ys (y :: acc)
+
+theorem mergeTR_go_eq : mergeTR.go le l₁ l₂ acc = acc.reverse ++ merge le l₁ l₂ := by
+  induction l₁ generalizing l₂ acc with
+  | nil => simp [mergeTR.go, merge, reverseAux_eq]
+  | cons x l₁ ih₁ =>
+    induction l₂ generalizing acc with
+    | nil => simp [mergeTR.go, merge, reverseAux_eq]
+    | cons y l₂ ih₂ =>
+      simp [mergeTR.go, merge]
+      split <;> simp [ih₁, ih₂]
+
+@[csimp] theorem merge_eq_mergeTR : @merge = @mergeTR := by
+  funext
+  simp [mergeTR, mergeTR_go_eq]
+
+/--
+Variant of `splitAt`, that does not reverse the first list, i.e
+`splitRevAt n l = ((l.take n).reverse, l.drop n)`.
+
+This exists solely as an optimization for `mergeSortTR` and `mergeSortTR₂`,
+and should not be used elsewhere.
+-/
+def splitRevAt (n : Nat) (l : List α) : List α × List α := go l n [] where
+  /-- Auxiliary for `splitAtRev`: `splitAtRev.go xs n acc = ((take n xs).reverse ++ acc, drop n xs)`. -/
+  go : List α → Nat → List α → List α × List α
+  | x :: xs, n+1, acc => go xs n (x :: acc)
+  | xs, _, acc => (acc, xs)
+
+theorem splitRevAt_go (xs : List α) (n : Nat) (acc : List α) :
+    splitRevAt.go xs n acc = ((take n xs).reverse ++ acc, drop n xs) := by
+  induction xs generalizing n acc with
+  | nil => simp [splitRevAt.go]
+  | cons x xs ih =>
+    cases n with
+    | zero => simp [splitRevAt.go]
+    | succ n =>
+      rw [splitRevAt.go, ih n (x :: acc), take_succ_cons, reverse_cons, drop_succ_cons,
+        append_assoc, singleton_append]
+
+theorem splitRevAt_eq (n : Nat) (l : List α) : splitRevAt n l = ((l.take n).reverse, l.drop n) := by
+  rw [splitRevAt, splitRevAt_go, append_nil]
+
+/--
+An intermediate speed-up for `mergeSort`.
+This version uses the tail-recurive `mergeTR` function as a subroutine.
+
+This is not the final version we use at runtime, as `mergeSortTR₂` is faster.
+This definition is useful as an intermediate step in proving the `@[csimp]` lemma for `mergeSortTR₂`.
+-/
+def mergeSortTR (le : α → α → Bool) (l : List α) : List α :=
+  run ⟨l, rfl⟩
+where run : {n : Nat} → { l : List α // l.length = n } → List α
+  | 0, ⟨[], _⟩ => []
+  | 1, ⟨[a], _⟩ => [a]
+  | n+2, xs =>
+    let (l, r) := splitInTwo xs
+    mergeTR le (run l) (run r)
+
+/--
+Split a list in two equal parts, reversing the first part.
+If the length is odd, the first part will be one element longer.
+-/
+def splitRevInTwo (l : { l : List α // l.length = n }) :
+    { l : List α // l.length = (n+1)/2 } × { l : List α // l.length = n/2 } :=
+  let r := splitRevAt ((n+1)/2) l.1
+  (⟨r.1, by simp [r, splitRevAt_eq, l.2]; omega⟩, ⟨r.2, by simp [r, splitRevAt_eq, l.2]; omega⟩)
+
+/--
+Split a list in two equal parts, reversing the first part.
+If the length is odd, the second part will be one element longer.
+-/
+def splitRevInTwo' (l : { l : List α // l.length = n }) :
+    { l : List α // l.length = n/2 } × { l : List α // l.length = (n+1)/2 } :=
+  let r := splitRevAt (n/2) l.1
+  (⟨r.1, by simp [r, splitRevAt_eq, l.2]; omega⟩, ⟨r.2, by simp [r, splitRevAt_eq, l.2]; omega⟩)
+
+/--
+Faster version of `mergeSortTR`, which avoids unnecessary list reversals.
+-/
+-- Per the benchmark in `tests/bench/mergeSort/`
+-- (which averages over 4 use cases: already sorted lists, reverse sorted lists, almost sorted lists, and random lists),
+-- for lists of length 10^6, `mergeSortTR₂` is about 20% faster than `mergeSortTR`.
+def mergeSortTR₂ (le : α → α → Bool) (l : List α) : List α :=
+  run ⟨l, rfl⟩
+where
+  run : {n : Nat} → { l : List α // l.length = n } → List α
+  | 0, ⟨[], _⟩ => []
+  | 1, ⟨[a], _⟩ => [a]
+  | n+2, xs =>
+    let (l, r) := splitRevInTwo xs
+    mergeTR le (run' l) (run r)
+  run' : {n : Nat} → { l : List α // l.length = n } → List α
+  | 0, ⟨[], _⟩ => []
+  | 1, ⟨[a], _⟩ => [a]
+  | n+2, xs =>
+    let (l, r) := splitRevInTwo' xs
+    mergeTR le (run' r) (run l)
+
+theorem splitRevInTwo'_fst (l : { l : List α // l.length = n }) :
+    (splitRevInTwo' l).1 = ⟨(splitInTwo ⟨l.1.reverse, by simpa using l.2⟩).2.1, by have := l.2; simp; omega⟩ := by
+  simp only [splitRevInTwo', splitRevAt_eq, reverse_take, splitInTwo_snd]
+  congr
+  have := l.2
+  omega
+theorem splitRevInTwo'_snd (l : { l : List α // l.length = n }) :
+    (splitRevInTwo' l).2 = ⟨(splitInTwo ⟨l.1.reverse, by simpa using l.2⟩).1.1.reverse, by have := l.2; simp; omega⟩ := by
+  simp only [splitRevInTwo', splitRevAt_eq, reverse_take, splitInTwo_fst, reverse_reverse]
+  congr 2
+  have := l.2
+  simp
+  omega
+theorem splitRevInTwo_fst (l : { l : List α // l.length = n }) :
+    (splitRevInTwo l).1 = ⟨(splitInTwo l).1.1.reverse, by have := l.2; simp; omega⟩ := by
+  simp only [splitRevInTwo, splitRevAt_eq, reverse_take, splitInTwo_fst]
+theorem splitRevInTwo_snd (l : { l : List α // l.length = n }) :
+    (splitRevInTwo l).2 = ⟨(splitInTwo l).2.1, by have := l.2; simp; omega⟩ := by
+  simp only [splitRevInTwo, splitRevAt_eq, reverse_take, splitInTwo_snd]
+
+theorem mergeSortTR_run_eq_mergeSort : {n : Nat} → (l : { l : List α // l.length = n }) → mergeSortTR.run le l = mergeSort le l.1
+  | 0, ⟨[], _⟩
+  | 1, ⟨[a], _⟩ => by simp [mergeSortTR.run, mergeSort]
+  | n+2, ⟨a :: b :: l, h⟩ => by
+    cases h
+    simp only [mergeSortTR.run, mergeSortTR.run, mergeSort]
+    rw [merge_eq_mergeTR]
+    rw [mergeSortTR_run_eq_mergeSort, mergeSortTR_run_eq_mergeSort]
+
+-- We don't make this a `@[csimp]` lemma because `mergeSort_eq_mergeSortTR₂` is faster.
+theorem mergeSort_eq_mergeSortTR : @mergeSort = @mergeSortTR := by
+  funext
+  rw [mergeSortTR, mergeSortTR_run_eq_mergeSort]
+
+-- This mutual block is unfortunately quite slow to elaborate.
+set_option maxHeartbeats 400000 in
+mutual
+theorem mergeSortTR₂_run_eq_mergeSort : {n : Nat} → (l : { l : List α // l.length = n }) → mergeSortTR₂.run le l = mergeSort le l.1
+  | 0, ⟨[], _⟩
+  | 1, ⟨[a], _⟩ => by simp [mergeSortTR₂.run, mergeSort]
+  | n+2, ⟨a :: b :: l, h⟩ => by
+    cases h
+    simp only [mergeSortTR₂.run, mergeSort]
+    rw [splitRevInTwo_fst, splitRevInTwo_snd]
+    rw [mergeSortTR₂_run_eq_mergeSort, mergeSortTR₂_run'_eq_mergeSort]
+    rw [merge_eq_mergeTR]
+    rw [reverse_reverse]
+termination_by n => n
+
+theorem mergeSortTR₂_run'_eq_mergeSort : {n : Nat} → (l : { l : List α // l.length = n }) → (w : l' = l.1.reverse) → mergeSortTR₂.run' le l = mergeSort le l'
+  | 0, ⟨[], _⟩, w
+  | 1, ⟨[a], _⟩, w => by simp_all [mergeSortTR₂.run', mergeSort]
+  | n+2, ⟨a :: b :: l, h⟩, w => by
+    cases h
+    simp only [mergeSortTR₂.run', mergeSort]
+    rw [splitRevInTwo'_fst, splitRevInTwo'_snd]
+    rw [mergeSortTR₂_run_eq_mergeSort, mergeSortTR₂_run'_eq_mergeSort _ rfl]
+    rw [← merge_eq_mergeTR]
+    have w' := congrArg length w
+    simp at w'
+    cases l' with
+    | nil => simp at w'
+    | cons x l' =>
+      cases l' with
+      | nil => simp at w'; omega
+      | cons y l' =>
+        rw [mergeSort]
+        congr 2
+        · dsimp at w
+          simp only [w]
+          simp only [splitInTwo_fst, splitInTwo_snd, reverse_take, take_reverse]
+          congr 1
+          rw [w, length_reverse]
+          simp
+        · dsimp at w
+          simp only [w]
+          simp only [reverse_cons, append_assoc, singleton_append, splitInTwo_snd, length_cons]
+          congr 1
+          simp at w'
+          omega
+termination_by n => n
+
+end
+
+@[csimp] theorem mergeSort_eq_mergeSortTR₂ : @mergeSort = @mergeSortTR₂ := by
+  funext
+  rw [mergeSortTR₂, mergeSortTR₂_run_eq_mergeSort]
+
+end List.MergeSort.Internal

src/Init/Data/List/Sort/Lemmas.lean

@@ -0,0 +1,399 @@
+/-
+Copyright (c) 2024 Lean FRO. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Kim Morrison
+-/
+prelude
+import Init.Data.List.Perm
+import Init.Data.List.Sort.Basic
+import Init.Data.Bool
+
+/-!
+# Basic properties of `mergeSort`.
+
+* `mergeSort_sorted`: `mergeSort` produces a sorted list.
+* `mergeSort_perm`: `mergeSort` is a permutation of the input list.
+* `mergeSort_of_sorted`: `mergeSort` does not change a sorted list.
+* `mergeSort_cons`: proves `mergeSort le (x :: xs) = l₁ ++ x :: l₂` for some `l₁, l₂`
+  so that `mergeSort le xs = l₁ ++ l₂`, and no `a ∈ l₁` satisfies `le a x`.
+* `mergeSort_stable`: if `c` is a sorted sublist of `l`, then `c` is still a sublist of `mergeSort le l`.
+
+-/
+
+namespace List
+
+-- We enable this instance locally so we can write `Sorted le` instead of `Sorted (le · ·)` everywhere.
+attribute [local instance] boolRelToRel
+
+variable {le : α → α → Bool}
+
+/-! ### splitInTwo -/
+
+@[simp] theorem splitInTwo_fst (l : { l : List α // l.length = n }) : (splitInTwo l).1 = ⟨l.1.take ((n+1)/2), by simp [splitInTwo, splitAt_eq, l.2]; omega⟩ := by
+  simp [splitInTwo, splitAt_eq]
+
+@[simp] theorem splitInTwo_snd (l : { l : List α // l.length = n }) : (splitInTwo l).2 = ⟨l.1.drop ((n+1)/2), by simp [splitInTwo, splitAt_eq, l.2]; omega⟩ := by
+  simp [splitInTwo, splitAt_eq]
+
+theorem splitInTwo_fst_append_splitInTwo_snd (l : { l : List α // l.length = n }) : (splitInTwo l).1.1 ++ (splitInTwo l).2.1 = l.1 := by
+  simp
+
+theorem splitInTwo_cons_cons_enumFrom_fst (i : Nat) (l : List α) :
+    (splitInTwo ⟨(i, a) :: (i+1, b) :: l.enumFrom (i+2), rfl⟩).1.1 =
+      (splitInTwo ⟨a :: b :: l, rfl⟩).1.1.enumFrom i := by
+  simp only [length_cons, splitInTwo_fst, enumFrom_length]
+  ext1 j
+  rw [getElem?_take, getElem?_enumFrom, getElem?_take]
+  split
+  · rw [getElem?_cons, getElem?_cons, getElem?_cons, getElem?_cons]
+    split
+    · simp; omega
+    · split
+      · simp; omega
+      · simp only [getElem?_enumFrom]
+        congr
+        ext <;> simp; omega
+  · simp
+
+theorem splitInTwo_cons_cons_enumFrom_snd (i : Nat) (l : List α) :
+    (splitInTwo ⟨(i, a) :: (i+1, b) :: l.enumFrom (i+2), rfl⟩).2.1 =
+      (splitInTwo ⟨a :: b :: l, rfl⟩).2.1.enumFrom (i+(l.length+3)/2) := by
+  simp only [length_cons, splitInTwo_snd, enumFrom_length]
+  ext1 j
+  rw [getElem?_drop, getElem?_enumFrom, getElem?_drop]
+  rw [getElem?_cons, getElem?_cons, getElem?_cons, getElem?_cons]
+  split
+  · simp; omega
+  · split
+    · simp; omega
+    · simp only [getElem?_enumFrom]
+      congr
+      ext <;> simp; omega
+
+theorem splitInTwo_fst_sorted (l : { l : List α // l.length = n }) (h : Pairwise le l.1) : Pairwise le (splitInTwo l).1.1 := by
+  rw [splitInTwo_fst]
+  exact h.take
+
+theorem splitInTwo_snd_sorted (l : { l : List α // l.length = n }) (h : Pairwise le l.1) : Pairwise le (splitInTwo l).2.1 := by
+  rw [splitInTwo_snd]
+  exact h.drop
+
+theorem splitInTwo_fst_le_splitInTwo_snd {l : { l : List α // l.length = n }} (h : Pairwise le l.1) :
+    ∀ a b, a ∈ (splitInTwo l).1.1 → b ∈ (splitInTwo l).2.1 → le a b := by
+  rw [splitInTwo_fst, splitInTwo_snd]
+  intro a b ma mb
+  exact h.rel_of_mem_take_of_mem_drop ma mb
+
+/-! ### enumLE -/
+
+theorem enumLE_trans (trans : ∀ a b c, le a b → le b c → le a c)
+    (a b c : Nat × α) : enumLE le a b → enumLE le b c → enumLE le a c := by
+  simp only [enumLE]
+  split <;> split <;> split <;> rename_i ab₂ ba₂ bc₂
+  · simp_all
+    intro ab₁
+    intro h
+    refine ⟨trans _ _ _ ab₂ bc₂, ?_⟩
+    rcases h with (cd₂ | bc₁)
+    · exact Or.inl (Decidable.byContradiction
+        (fun ca₂ => by simp_all [trans _ _ _ (by simpa using ca₂) ab₂]))
+    · exact Or.inr (Nat.le_trans ab₁ bc₁)
+  · simp_all
+  · simp_all
+    intro h
+    refine ⟨trans _ _ _ ab₂ bc₂, ?_⟩
+    left
+    rcases h with (cb₂ | _)
+    · exact (Decidable.byContradiction
+        (fun ca₂ => by simp_all [trans _ _ _ (by simpa using ca₂) ab₂]))
+    · exact (Decidable.byContradiction
+        (fun ca₂ => by simp_all [trans _ _ _ bc₂ (by simpa using ca₂)]))
+  · simp_all
+  · simp_all
+  · simp_all
+  · simp_all
+  · simp_all
+
+theorem enumLE_total (total : ∀ a b, !le a b → le b a)
+    (a b : Nat × α) : !enumLE le a b → enumLE le b a := by
+  simp only [enumLE]
+  split <;> split
+  · simpa using Nat.le_of_lt
+  · simp
+  · simp
+  · simp_all [total a.2 b.2]
+
+/-! ### merge -/
+
+theorem merge_stable : ∀ (xs ys) (_ : ∀ x y, x ∈ xs → y ∈ ys → x.1 ≤ y.1),
+    (merge (enumLE le) xs ys).map (·.2) = merge le (xs.map (·.2)) (ys.map (·.2))
+  | [], ys, _ => by simp [merge]
+  | xs, [], _ => by simp [merge]
+  | (i, x) :: xs, (j, y) :: ys, h => by
+    simp only [merge, enumLE, map_cons]
+    split <;> rename_i w
+    · rw [if_pos (by simp [h _ _ (mem_cons_self ..) (mem_cons_self ..)])]
+      simp only [map_cons, cons.injEq, true_and]
+      rw [merge_stable, map_cons]
+      exact fun x' y' mx my => h x' y' (mem_cons_of_mem (i, x) mx) my
+    · simp only [↓reduceIte, map_cons, cons.injEq, true_and]
+      rw [merge_stable, map_cons]
+      exact fun x' y' mx my => h x' y' mx (mem_cons_of_mem (j, y) my)
+
+/--
+The elements of `merge le xs ys` are exactly the elements of `xs` and `ys`.
+-/
+-- We subsequently prove that `mergeSort_perm : merge le xs ys ~ xs ++ ys`.
+theorem mem_merge {a : α} {xs ys : List α} : a ∈ merge le xs ys ↔ a ∈ xs ∨ a ∈ ys := by
+  induction xs generalizing ys with
+  | nil => simp [merge]
+  | cons x xs ih =>
+    induction ys with
+    | nil => simp [merge]
+    | cons y ys ih =>
+      simp only [merge]
+      split <;> rename_i h
+      · simp_all [or_assoc]
+      · simp only [mem_cons, or_assoc, Bool.not_eq_true, ih, ← or_assoc]
+        apply or_congr_left
+        simp only [or_comm (a := a = y), or_assoc]
+
+/--
+If the ordering relation `le` is transitive and total (i.e. `le a b ∨ le b a` for all `a, b`)
+then the `merge` of two sorted lists is sorted.
+-/
+theorem merge_sorted
+    (trans : ∀ (a b c : α), le a b → le b c → le a c)
+    (total : ∀ (a b : α), !le a b → le b a)
+    (l₁ l₂ : List α) (h₁ : l₁.Pairwise le) (h₂ : l₂.Pairwise le) : (merge le l₁ l₂).Pairwise le := by
+  induction l₁ generalizing l₂ with
+  | nil => simpa only [merge]
+  | cons x l₁ ih₁ =>
+    induction l₂ with
+    | nil => simpa only [merge]
+    | cons y l₂ ih₂ =>
+      simp only [merge]
+      split <;> rename_i h
+      · apply Pairwise.cons
+        · intro z m
+          rw [mem_merge, mem_cons] at m
+          rcases m with (m|rfl|m)
+          · exact rel_of_pairwise_cons h₁ m
+          · exact h
+          · exact trans _ _ _ h (rel_of_pairwise_cons h₂ m)
+        · exact ih₁ _ h₁.tail h₂
+      · apply Pairwise.cons
+        · intro z m
+          rw [mem_merge, mem_cons] at m
+          rcases m with (⟨rfl|m⟩|m)
+          · exact total _ _ (by simpa using h)
+          · exact trans _ _ _ (total _ _ (by simpa using h)) (rel_of_pairwise_cons h₁ m)
+          · exact rel_of_pairwise_cons h₂ m
+        · exact ih₂ h₂.tail
+
+theorem merge_of_le : ∀ {xs ys : List α} (_ : ∀ a b, a ∈ xs → b ∈ ys → le a b),
+    merge le xs ys = xs ++ ys
+  | [], ys, _
+  | xs, [], _ => by simp [merge]
+  | x :: xs, y :: ys, h => by
+    simp only [merge, cons_append]
+    rw [if_pos, merge_of_le]
+    · intro a b ma mb
+      exact h a b (mem_cons_of_mem _ ma) mb
+    · exact h x y (mem_cons_self _ _) (mem_cons_self _ _)
+
+variable (le) in
+theorem merge_perm_append : ∀ {xs ys : List α}, merge le xs ys ~ xs ++ ys
+  | [], ys => by simp [merge]
+  | xs, [] => by simp [merge]
+  | x :: xs, y :: ys => by
+    simp only [merge]
+    split
+    · exact merge_perm_append.cons x
+    · exact (merge_perm_append.cons y).trans
+        ((Perm.swap x y _).trans (perm_middle.symm.cons x))
+
+/-! ### mergeSort -/
+
+variable (le) in
+theorem mergeSort_perm : ∀ (l : List α), mergeSort le l ~ l
+  | [] => by simp [mergeSort]
+  | [a] => by simp [mergeSort]
+  | a :: b :: xs => by
+    simp only [mergeSort]
+    have : (splitInTwo ⟨a :: b :: xs, rfl⟩).1.1.length < xs.length + 1 + 1 := by simp [splitInTwo_fst]; omega
+    have : (splitInTwo ⟨a :: b :: xs, rfl⟩).2.1.length < xs.length + 1 + 1 := by simp [splitInTwo_snd]; omega
+    exact (merge_perm_append le).trans
+      (((mergeSort_perm _).append (mergeSort_perm _)).trans
+        (Perm.of_eq (splitInTwo_fst_append_splitInTwo_snd _)))
+termination_by l => l.length
+
+@[simp] theorem mem_mergeSort {a : α} {l : List α} : a ∈ mergeSort le l ↔ a ∈ l :=
+  (mergeSort_perm le l).mem_iff
+
+/--
+The result of `mergeSort` is sorted,
+as long as the comparison function is transitive (`le a b → le b c → le a c`)
+and total in the sense that `le a b ∨ le b a`.
+
+The comparison function need not be irreflexive, i.e. `le a b` and `le b a` is allowed even when `a ≠ b`.
+-/
+theorem mergeSort_sorted
+    (trans : ∀ (a b c : α), le a b → le b c → le a c)
+    (total : ∀ (a b : α), !le a b → le b a) :
+    (l : List α) → (mergeSort le l).Pairwise le
+  | [] => by simp [mergeSort]
+  | [a] => by simp [mergeSort]
+  | a :: b :: xs => by
+    have : (splitInTwo ⟨a :: b :: xs, rfl⟩).1.1.length < xs.length + 1 + 1 := by simp [splitInTwo_fst]; omega
+    have : (splitInTwo ⟨a :: b :: xs, rfl⟩).2.1.length < xs.length + 1 + 1 := by simp [splitInTwo_snd]; omega
+    rw [mergeSort]
+    apply merge_sorted @trans @total
+    apply mergeSort_sorted trans total
+    apply mergeSort_sorted trans total
+termination_by l => l.length
+
+/--
+If the input list is already sorted, then `mergeSort` does not change the list.
+-/
+theorem mergeSort_of_sorted : ∀ {l : List α} (_ : Pairwise le l), mergeSort le l = l
+  | [], _ => by simp [mergeSort]
+  | [a], _ => by simp [mergeSort]
+  | a :: b :: xs, h => by
+    have : (splitInTwo ⟨a :: b :: xs, rfl⟩).1.1.length < xs.length + 1 + 1 := by simp [splitInTwo_fst]; omega
+    have : (splitInTwo ⟨a :: b :: xs, rfl⟩).2.1.length < xs.length + 1 + 1 := by simp [splitInTwo_snd]; omega
+    rw [mergeSort]
+    rw [mergeSort_of_sorted (splitInTwo_fst_sorted ⟨a :: b :: xs, rfl⟩ h)]
+    rw [mergeSort_of_sorted (splitInTwo_snd_sorted ⟨a :: b :: xs, rfl⟩ h)]
+    rw [merge_of_le (splitInTwo_fst_le_splitInTwo_snd h)]
+    rw [splitInTwo_fst_append_splitInTwo_snd]
+termination_by l => l.length
+
+/--
+This merge sort algorithm is stable,
+in the sense that breaking ties in the ordering function using the position in the list
+has no effect on the output.
+
+That is, elements which are equal with respect to the ordering function will remain
+in the same order in the output list as they were in the input list.
+
+See also:
+* `mergeSort_stable`: if `c <+ l` and `c.Pairwise le`, then `c <+ mergeSort le l`.
+* `mergeSort_stable_pair`: if `[a, b] <+ l` and `le a b`, then `[a, b] <+ mergeSort le l`)
+-/
+theorem mergeSort_enum {l : List α} :
+    (mergeSort (enumLE le) (l.enum)).map (·.2) = mergeSort le l :=
+  go 0 l
+where go : ∀ (i : Nat) (l : List α),
+    (mergeSort (enumLE le) (l.enumFrom i)).map (·.2) = mergeSort le l
+  | _, []
+  | _, [a] => by simp [mergeSort]
+  | _, a :: b :: xs => by
+    have : (splitInTwo ⟨a :: b :: xs, rfl⟩).1.1.length < xs.length + 1 + 1 := by simp [splitInTwo_fst]; omega
+    have : (splitInTwo ⟨a :: b :: xs, rfl⟩).2.1.length < xs.length + 1 + 1 := by simp [splitInTwo_snd]; omega
+    simp only [mergeSort, enumFrom]
+    rw [splitInTwo_cons_cons_enumFrom_fst]
+    rw [splitInTwo_cons_cons_enumFrom_snd]
+    rw [merge_stable]
+    · rw [go, go]
+    · simp only [mem_mergeSort, Prod.forall]
+      intros j x k y mx my
+      have := mem_enumFrom mx
+      have := mem_enumFrom my
+      simp_all
+      omega
+termination_by _ l => l.length
+
+theorem mergeSort_cons {le : α → α → Bool}
+    (trans : ∀ (a b c : α), le a b → le b c → le a c)
+    (total : ∀ (a b : α), !le a b → le b a)
+    (a : α) (l : List α) :
+    ∃ l₁ l₂, mergeSort le (a :: l) = l₁ ++ a :: l₂ ∧ mergeSort le l = l₁ ++ l₂ ∧
+      ∀ b, b ∈ l₁ → !le a b := by
+  rw [← mergeSort_enum]
+  rw [enum_cons]
+  have nd : Nodup ((a :: l).enum.map (·.1)) := by rw [enum_map_fst]; exact nodup_range _
+  have m₁ : (0, a) ∈ mergeSort (enumLE le) ((a :: l).enum) :=
+    mem_mergeSort.mpr (mem_cons_self _ _)
+  obtain ⟨l₁, l₂, h⟩ := append_of_mem m₁
+  have s := mergeSort_sorted (enumLE_trans trans) (enumLE_total total) ((a :: l).enum)
+  rw [h] at s
+  have p := mergeSort_perm (enumLE le) ((a :: l).enum)
+  rw [h] at p
+  refine ⟨l₁.map (·.2), l₂.map (·.2), ?_, ?_, ?_⟩
+  · simpa using congrArg (·.map (·.2)) h
+  · rw [← mergeSort_enum.go 1, ← map_append]
+    congr 1
+    have q : mergeSort (enumLE le) (enumFrom 1 l) ~ l₁ ++ l₂ :=
+      (mergeSort_perm (enumLE le) (enumFrom 1 l)).trans
+        (p.symm.trans perm_middle).cons_inv
+    apply Perm.eq_of_sorted (le := enumLE le)
+    · rintro ⟨i, a⟩ ⟨j, b⟩  ha hb
+      simp only [mem_mergeSort] at ha
+      simp only [← q.mem_iff, mem_mergeSort] at hb
+      simp only [enumLE]
+      simp only [Bool.if_false_right, Bool.and_eq_true, Prod.mk.injEq, and_imp]
+      intro ab h ba h'
+      simp only [Bool.decide_eq_true] at ba
+      replace h : i ≤ j := by simpa [ab, ba] using h
+      replace h' : j ≤ i := by simpa [ab, ba] using h'
+      cases Nat.le_antisymm h h'
+      constructor
+      · rfl
+      · have := mem_enumFrom ha
+        have := mem_enumFrom hb
+        simp_all
+    · exact mergeSort_sorted (enumLE_trans trans) (enumLE_total total) ..
+    · exact s.sublist ((sublist_cons_self (0, a) l₂).append_left l₁)
+    · exact q
+  · intro b m
+    simp only [mem_map, Prod.exists, exists_eq_right] at m
+    obtain ⟨j, m⟩ := m
+    replace p := p.map (·.1)
+    have nd' := nd.perm p.symm
+    rw [map_append] at nd'
+    have j0 := nd'.rel_of_mem_append
+      (mem_map_of_mem (·.1) m) (mem_map_of_mem _ (mem_cons_self _ _))
+    simp only [ne_eq] at j0
+    have r := s.rel_of_mem_append m (mem_cons_self _ _)
+    simp_all [enumLE]
+
+/--
+Another statement of stability of merge sort.
+If `c` is a sorted sublist of `l`,
+then `c` is still a sublist of `mergeSort le l`.
+-/
+theorem mergeSort_stable
+    (trans : ∀ (a b c : α), le a b → le b c → le a c)
+    (total : ∀ (a b : α), !le a b → le b a) :
+    ∀ {c : List α} (_ : c.Pairwise le) (_ : c <+ l),
+    c <+ mergeSort le l
+  | _, _, .slnil => nil_sublist _
+  | c, hc, @Sublist.cons _ _ l a h => by
+    obtain ⟨l₁, l₂, h₁, h₂, -⟩ := mergeSort_cons trans total a l
+    rw [h₁]
+    have h' := mergeSort_stable trans total hc h
+    rw [h₂] at h'
+    exact h'.middle a
+  | _, _, @Sublist.cons₂ _ l₁ l₂ a h => by
+    rename_i hc
+    obtain ⟨l₃, l₄, h₁, h₂, h₃⟩ := mergeSort_cons trans total a l₂
+    rw [h₁]
+    have h' := mergeSort_stable trans total hc.tail h
+    rw [h₂] at h'
+    simp only [Bool.not_eq_true', tail_cons] at h₃ h'
+    exact
+      sublist_append_of_sublist_right (Sublist.cons₂ a
+        ((fun w => Sublist.of_sublist_append_right w h') fun b m₁ m₃ =>
+          (Bool.eq_not_self true).mp ((rel_of_pairwise_cons hc m₁).symm.trans (h₃ b m₃))))
+
+/--
+Another statement of stability of merge sort.
+If a pair `[a, b]` is a sublist of `l` and `le a b`,
+then `[a, b]` is still a sublist of `mergeSort le l`.
+-/
+theorem mergeSort_stable_pair
+    (trans : ∀ (a b c : α), le a b → le b c → le a c)
+    (total : ∀ (a b : α), !le a b → le b a)
+    (hab : le a b) (h : [a, b] <+ l) : [a, b] <+ mergeSort le l :=
+  mergeSort_stable trans total (pairwise_pair.mpr hab) h

src/Init/Data/List/TakeDrop.lean

@@ -5,500 +5,459 @@ Authors: Parikshit Khanna, Jeremy Avigad, Leonardo de Moura, Floris van Doorn, M
 -/
 prelude
 import Init.Data.List.Lemmas
-import Init.Data.Nat.Lemmas
 
 /-!
-# Further lemmas about `List.take`, `List.drop`, `List.zip` and `List.zipWith`.
-
-These are in a separate file from most of the list lemmas
-as they required importing more lemmas about natural numbers, and use `omega`.
+# Lemmas about `List.zip`, `List.zipWith`, `List.zipWithAll`, and `List.unzip`.
 -/
 
 namespace List
 
 open Nat
 
-/-! ### take -/
+/-! ### take and drop
 
-@[simp] theorem length_take : ∀ (i : Nat) (l : List α), length (take i l) = min i (length l)
-  | 0, l => by simp [Nat.zero_min]
-  | succ n, [] => by simp [Nat.min_zero]
-  | succ n, _ :: l => by simp [Nat.succ_min_succ, length_take]
+Further results on `List.take` and `List.drop`, which rely on stronger automation in `Nat`,
+are given in `Init.Data.List.TakeDrop`.
+-/
 
-theorem length_take_le (n) (l : List α) : length (take n l) ≤ n := by simp [Nat.min_le_left]
-
-theorem length_take_le' (n) (l : List α) : length (take n l) ≤ l.length :=
-  by simp [Nat.min_le_right]
-
-theorem length_take_of_le (h : n ≤ length l) : length (take n l) = n := by simp [Nat.min_eq_left h]
-
-theorem take_take : ∀ (n m) (l : List α), take n (take m l) = take (min n m) l
-  | n, 0, l => by rw [Nat.min_zero, take_zero, take_nil]
-  | 0, m, l => by rw [Nat.zero_min, take_zero, take_zero]
-  | succ n, succ m, nil => by simp only [take_nil]
-  | succ n, succ m, a :: l => by
-    simp only [take, succ_min_succ, take_take n m l]
-
-@[simp] theorem take_replicate (a : α) : ∀ n m : Nat, take n (replicate m a) = replicate (min n m) a
-  | n, 0 => by simp [Nat.min_zero]
-  | 0, m => by simp [Nat.zero_min]
-  | succ n, succ m => by simp [replicate_succ, succ_min_succ, take_replicate]
-
-@[simp] theorem drop_replicate (a : α) : ∀ n m : Nat, drop n (replicate m a) = replicate (m - n) a
-  | n, 0 => by simp
-  | 0, m => by simp
-  | succ n, succ m => by simp [replicate_succ, succ_sub_succ, drop_replicate]
-
-/-- Taking the first `n` elements in `l₁ ++ l₂` is the same as appending the first `n` elements
-of `l₁` to the first `n - l₁.length` elements of `l₂`. -/
-theorem take_append_eq_append_take {l₁ l₂ : List α} {n : Nat} :
-    take n (l₁ ++ l₂) = take n l₁ ++ take (n - l₁.length) l₂ := by
-  induction l₁ generalizing n
-  · simp
-  · cases n
-    · simp [*]
-    · simp only [cons_append, take_cons_succ, length_cons, succ_eq_add_one, cons.injEq,
-        append_cancel_left_eq, true_and, *]
-      congr 1
-      omega
-
-theorem take_append_of_le_length {l₁ l₂ : List α} {n : Nat} (h : n ≤ l₁.length) :
-    (l₁ ++ l₂).take n = l₁.take n := by
-  simp [take_append_eq_append_take, Nat.sub_eq_zero_of_le h]
-
-/-- Taking the first `l₁.length + i` elements in `l₁ ++ l₂` is the same as appending the first
-`i` elements of `l₂` to `l₁`. -/
-theorem take_append {l₁ l₂ : List α} (i : Nat) :
-    take (l₁.length + i) (l₁ ++ l₂) = l₁ ++ take i l₂ := by
-  rw [take_append_eq_append_take, take_all_of_le (Nat.le_add_right _ _), Nat.add_sub_cancel_left]
-
-/-- The `i`-th element of a list coincides with the `i`-th element of any of its prefixes of
-length `> i`. Version designed to rewrite from the big list to the small list. -/
-theorem getElem_take (L : List α) {i j : Nat} (hi : i < L.length) (hj : i < j) :
-    L[i] = (L.take j)[i]'(length_take .. ▸ Nat.lt_min.mpr ⟨hj, hi⟩) :=
-  getElem_of_eq (take_append_drop j L).symm _ ▸ getElem_append ..
-
-/-- The `i`-th element of a list coincides with the `i`-th element of any of its prefixes of
-length `> i`. Version designed to rewrite from the small list to the big list. -/
-theorem getElem_take' (L : List α) {j i : Nat} {h : i < (L.take j).length} :
-    (L.take j)[i] =
-    L[i]'(Nat.lt_of_lt_of_le h (length_take_le' _ _)) := by
-  rw [length_take, Nat.lt_min] at h; rw [getElem_take L _ h.1]
-
-/-- The `i`-th element of a list coincides with the `i`-th element of any of its prefixes of
-length `> i`. Version designed to rewrite from the big list to the small list. -/
-@[deprecated getElem_take (since := "2024-06-12")]
-theorem get_take (L : List α) {i j : Nat} (hi : i < L.length) (hj : i < j) :
-    get L ⟨i, hi⟩ = get (L.take j) ⟨i, length_take .. ▸ Nat.lt_min.mpr ⟨hj, hi⟩⟩ := by
-  simp [getElem_take _ hi hj]
-
-/-- The `i`-th element of a list coincides with the `i`-th element of any of its prefixes of
-length `> i`. Version designed to rewrite from the small list to the big list. -/
-@[deprecated getElem_take (since := "2024-06-12")]
-theorem get_take' (L : List α) {j i} :
-    get (L.take j) i =
-    get L ⟨i.1, Nat.lt_of_lt_of_le i.2 (length_take_le' _ _)⟩ := by
-  simp [getElem_take']
-
-theorem getElem?_take_eq_none {l : List α} {n m : Nat} (h : n ≤ m) :
-    (l.take n)[m]? = none :=
-  getElem?_eq_none <| Nat.le_trans (length_take_le _ _) h
-
-@[deprecated getElem?_take_eq_none (since := "2024-06-12")]
-theorem get?_take_eq_none {l : List α} {n m : Nat} (h : n ≤ m) :
-    (l.take n).get? m = none := by
-  simp [getElem?_take_eq_none h]
-
-theorem getElem?_take_eq_if {l : List α} {n m : Nat} :
-    (l.take n)[m]? = if m < n then l[m]? else none := by
-  split
-  · next h => exact getElem?_take h
-  · next h => exact getElem?_take_eq_none (Nat.le_of_not_lt h)
-
-@[deprecated getElem?_take_eq_if (since := "2024-06-12")]
-theorem get?_take_eq_if {l : List α} {n m : Nat} :
-    (l.take n).get? m = if m < n then l.get? m else none := by
-  simp [getElem?_take_eq_if]
-
-theorem head?_take {l : List α} {n : Nat} :
-    (l.take n).head? = if n = 0 then none else l.head? := by
-  simp [head?_eq_getElem?, getElem?_take_eq_if]
-  split
-  · rw [if_neg (by omega)]
-  · rw [if_pos (by omega)]
-
-theorem head_take {l : List α} {n : Nat} (h : l.take n ≠ []) :
-    (l.take n).head h = l.head (by simp_all) := by
-  apply Option.some_inj.1
-  rw [← head?_eq_head, ← head?_eq_head, head?_take, if_neg]
-  simp_all
-
-theorem getLast?_take {l : List α} : (l.take n).getLast? = if n = 0 then none else l[n - 1]?.or l.getLast? := by
-  rw [getLast?_eq_getElem?, getElem?_take_eq_if, length_take]
-  split
-  · rw [if_neg (by omega)]
-    rw [Nat.min_def]
-    split
-    · rw [getElem?_eq_getElem (by omega)]
-      simp
-    · rw [← getLast?_eq_getElem?, getElem?_eq_none (by omega)]
-      simp
-  · rw [if_pos]
-    omega
-
-theorem getLast_take {l : List α} (h : l.take n ≠ []) :
-    (l.take n).getLast h = l[n - 1]?.getD (l.getLast (by simp_all)) := by
-  rw [getLast_eq_getElem, getElem_take']
-  simp [length_take, Nat.min_def]
-  simp at h
-  split
-  · rw [getElem?_eq_getElem (by omega)]
-    simp
-  · rw [getElem?_eq_none (by omega), getLast_eq_getElem]
-    simp
+theorem take_cons {l : List α} (h : 0 < n) : take n (a :: l) = a :: take (n - 1) l := by
+  cases n with
+  | zero => exact absurd h (Nat.lt_irrefl _)
+  | succ n => rfl
 
 @[simp]
-theorem take_eq_take :
-    ∀ {l : List α} {m n : Nat}, l.take m = l.take n ↔ min m l.length = min n l.length
-  | [], m, n => by simp [Nat.min_zero]
-  | _ :: xs, 0, 0 => by simp
-  | x :: xs, m + 1, 0 => by simp [Nat.zero_min, succ_min_succ]
-  | x :: xs, 0, n + 1 => by simp [Nat.zero_min, succ_min_succ]
-  | x :: xs, m + 1, n + 1 => by simp [succ_min_succ, take_eq_take]; omega
+theorem drop_one : ∀ l : List α, drop 1 l = tail l
+  | [] | _ :: _ => rfl
 
-theorem take_add (l : List α) (m n : Nat) : l.take (m + n) = l.take m ++ (l.drop m).take n := by
-  suffices take (m + n) (take m l ++ drop m l) = take m l ++ take n (drop m l) by
-    rw [take_append_drop] at this
-    assumption
-  rw [take_append_eq_append_take, take_all_of_le, append_right_inj]
-  · simp only [take_eq_take, length_take, length_drop]
-    omega
-  apply Nat.le_trans (m := m)
-  · apply length_take_le
-  · apply Nat.le_add_right
+@[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
 
-theorem dropLast_take {n : Nat} {l : List α} (h : n < l.length) :
-    (l.take n).dropLast = l.take n.pred := by
-  simp only [dropLast_eq_take, length_take, Nat.le_of_lt h, take_take, pred_le, Nat.min_eq_left]
+@[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 map_eq_append_split {f : α → β} {l : List α} {s₁ s₂ : List β}
-    (h : map f l = s₁ ++ s₂) : ∃ l₁ l₂, l = l₁ ++ l₂ ∧ map f l₁ = s₁ ∧ map f l₂ = s₂ := by
-  have := h
-  rw [← take_append_drop (length s₁) l] at this ⊢
-  rw [map_append] at this
-  refine ⟨_, _, rfl, append_inj this ?_⟩
-  rw [length_map, length_take, Nat.min_eq_left]
-  rw [← length_map l f, h, length_append]
-  apply Nat.le_add_right
+theorem drop_of_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)
 
-/-! ### drop -/
+theorem length_lt_of_drop_ne_nil {l : List α} {n} (h : drop n l ≠ []) : n < l.length :=
+  gt_of_not_le (mt drop_of_length_le h)
 
-theorem drop_length_cons {l : List α} (h : l ≠ []) (a : α) :
-    (a :: l).drop l.length = [l.getLast h] := by
-  induction l generalizing a with
-  | nil =>
-    cases h rfl
-  | cons y l ih =>
-    simp only [drop, length]
-    by_cases h₁ : l = []
-    · simp [h₁]
-    rw [getLast_cons' _ h₁]
-    exact ih h₁ y
+theorem take_of_length_le {l : List α} (h : l.length ≤ i) : take i l = l := by
+  have := take_append_drop i l
+  rw [drop_of_length_le h, append_nil] at this; exact this
 
-/-- Dropping the elements up to `n` in `l₁ ++ l₂` is the same as dropping the elements up to `n`
-in `l₁`, dropping the elements up to `n - l₁.length` in `l₂`, and appending them. -/
-theorem drop_append_eq_append_drop {l₁ l₂ : List α} {n : Nat} :
-    drop n (l₁ ++ l₂) = drop n l₁ ++ drop (n - l₁.length) l₂ := by
-  induction l₁ generalizing n
-  · simp
-  · cases n
-    · simp [*]
-    · simp only [cons_append, drop_succ_cons, length_cons, succ_eq_add_one, append_cancel_left_eq, *]
-      congr 1
-      omega
+theorem lt_length_of_take_ne_self {l : List α} {n} (h : l.take n ≠ l) : n < l.length :=
+  gt_of_not_le (mt take_of_length_le h)
 
-theorem drop_append_of_le_length {l₁ l₂ : List α} {n : Nat} (h : n ≤ l₁.length) :
-    (l₁ ++ l₂).drop n = l₁.drop n ++ l₂ := by
-  simp [drop_append_eq_append_drop, Nat.sub_eq_zero_of_le h]
+@[deprecated drop_of_length_le (since := "2024-07-07")] abbrev drop_length_le := @drop_of_length_le
+@[deprecated take_of_length_le (since := "2024-07-07")] abbrev take_length_le := @take_of_length_le
 
+@[simp] theorem drop_length (l : List α) : drop l.length l = [] := drop_of_length_le (Nat.le_refl _)
 
-/-- Dropping the elements up to `l₁.length + i` in `l₁ + l₂` is the same as dropping the elements
-up to `i` in `l₂`. -/
-@[simp]
-theorem drop_append {l₁ l₂ : List α} (i : Nat) : drop (l₁.length + i) (l₁ ++ l₂) = drop i l₂ := by
-  rw [drop_append_eq_append_drop, drop_eq_nil_of_le] <;>
-    simp [Nat.add_sub_cancel_left, Nat.le_add_right]
-
-theorem lt_length_drop (L : List α) {i j : Nat} (h : i + j < L.length) : j < (L.drop i).length := by
-  have A : i < L.length := Nat.lt_of_le_of_lt (Nat.le.intro rfl) h
-  rw [(take_append_drop i L).symm] at h
-  simpa only [Nat.le_of_lt A, Nat.min_eq_left, Nat.add_lt_add_iff_left, length_take,
-    length_append] using h
-
-/-- The `i + j`-th element of a list coincides with the `j`-th element of the list obtained by
-dropping the first `i` elements. Version designed to rewrite from the big list to the small list. -/
-theorem getElem_drop (L : List α) {i j : Nat} (h : i + j < L.length) :
-    L[i + j] = (L.drop i)[j]'(lt_length_drop L h) := by
-  have : i ≤ L.length := Nat.le_trans (Nat.le_add_right _ _) (Nat.le_of_lt h)
-  rw [getElem_of_eq (take_append_drop i L).symm h, getElem_append_right'] <;>
-    simp [Nat.min_eq_left this, Nat.add_sub_cancel_left, Nat.le_add_right]
-
-/-- The `i + j`-th element of a list coincides with the `j`-th element of the list obtained by
-dropping the first `i` elements. Version designed to rewrite from the big list to the small list. -/
-@[deprecated getElem_drop (since := "2024-06-12")]
-theorem get_drop (L : List α) {i j : Nat} (h : i + j < L.length) :
-    get L ⟨i + j, h⟩ = get (L.drop i) ⟨j, lt_length_drop L h⟩ := by
-  simp [getElem_drop]
-
-/-- The `i + j`-th element of a list coincides with the `j`-th element of the list obtained by
-dropping the first `i` elements. Version designed to rewrite from the small list to the big list. -/
-theorem getElem_drop' (L : List α) {i : Nat} {j : Nat} {h : j < (L.drop i).length} :
-    (L.drop i)[j] = L[i + j]'(by
-      rw [Nat.add_comm]
-      exact Nat.add_lt_of_lt_sub (length_drop i L ▸ h)) := by
-  rw [getElem_drop]
-
-/-- The `i + j`-th element of a list coincides with the `j`-th element of the list obtained by
-dropping the first `i` elements. Version designed to rewrite from the small list to the big list. -/
-@[deprecated getElem_drop' (since := "2024-06-12")]
-theorem get_drop' (L : List α) {i j} :
-    get (L.drop i) j = get L ⟨i + j, by
-      rw [Nat.add_comm]
-      exact Nat.add_lt_of_lt_sub (length_drop i L ▸ j.2)⟩ := by
-  simp [getElem_drop']
+@[simp] theorem take_length (l : List α) : take l.length l = l := take_of_length_le (Nat.le_refl _)
 
 @[simp]
-theorem getElem?_drop (L : List α) (i j : Nat) : (L.drop i)[j]? = L[i + j]? := by
-  ext
-  simp only [getElem?_eq_some, getElem_drop', Option.mem_def]
-  constructor <;> intro ⟨h, ha⟩
-  · exact ⟨_, ha⟩
-  · refine ⟨?_, ha⟩
-    rw [length_drop]
-    rw [Nat.add_comm] at h
-    apply Nat.lt_sub_of_add_lt h
+theorem getElem_cons_drop : ∀ (l : List α) (i : Nat) (h : i < l.length),
+    l[i] :: drop (i + 1) l = drop i l
+  | _::_, 0, _ => rfl
+  | _::_, i+1, _ => getElem_cons_drop _ i _
 
-@[deprecated getElem?_drop (since := "2024-06-12")]
-theorem get?_drop (L : List α) (i j : Nat) : get? (L.drop i) j = get? L (i + j) := by
+@[deprecated getElem_cons_drop (since := "2024-06-12")]
+theorem get_cons_drop (l : List α) (i) : get l i :: drop (i + 1) l = drop i l := by
   simp
 
-theorem head?_drop (l : List α) (n : Nat) :
-    (l.drop n).head? = l[n]? := by
-  rw [head?_eq_getElem?, getElem?_drop, Nat.add_zero]
+theorem drop_eq_getElem_cons {n} {l : List α} (h) : drop n l = l[n] :: drop (n + 1) l :=
+  (getElem_cons_drop _ n h).symm
 
-theorem head_drop {l : List α} {n : Nat} (h : l.drop n ≠ []) :
-    (l.drop n).head h = l[n]'(by simp_all) := by
-  have w : n < l.length := length_lt_of_drop_ne_nil h
-  simpa [head?_eq_head, getElem?_eq_getElem, h, w] using head?_drop l n
+@[deprecated drop_eq_getElem_cons (since := "2024-06-12")]
+theorem drop_eq_get_cons {n} {l : List α} (h) : drop n l = get l ⟨n, h⟩ :: drop (n + 1) l := by
+  simp [drop_eq_getElem_cons]
 
-theorem getLast?_drop {l : List α} : (l.drop n).getLast? = if l.length ≤ n then none else l.getLast? := by
-  rw [getLast?_eq_getElem?, getElem?_drop]
-  rw [length_drop]
-  split
-  · rw [getElem?_eq_none (by omega)]
-  · rw [getLast?_eq_getElem?]
-    congr
-    omega
+@[simp]
+theorem getElem?_take_of_lt {l : List α} {n m : Nat} (h : m < n) : (l.take n)[m]? = l[m]? := by
+  induction n generalizing l m with
+  | zero =>
+    exact absurd h (Nat.not_lt_of_le m.zero_le)
+  | succ _ hn =>
+    cases l with
+    | nil => simp only [take_nil]
+    | cons hd tl =>
+      cases m
+      · simp
+      · simpa using hn (Nat.lt_of_succ_lt_succ h)
 
-theorem getLast_drop {l : List α} (h : l.drop n ≠ []) :
-    (l.drop n).getLast h = l.getLast (ne_nil_of_length_pos (by simp at h; omega)) := by
-  simp only [ne_eq, drop_eq_nil_iff_le] at h
-  apply Option.some_inj.1
-  simp only [← getLast?_eq_getLast, getLast?_drop, ite_eq_right_iff]
-  omega
+@[deprecated getElem?_take_of_lt (since := "2024-06-12")]
+theorem get?_take {l : List α} {n m : Nat} (h : m < n) : (l.take n).get? m = l.get? m := by
+  simp [getElem?_take_of_lt, h]
 
-theorem set_eq_take_append_cons_drop {l : List α} {n : Nat} {a : α} :
-    l.set n a = if n < l.length then l.take n ++ a :: l.drop (n + 1) else l := by
-  split <;> rename_i h
-  · ext1 m
-    by_cases h' : m < n
-    · rw [getElem?_append (by simp [length_take]; omega), getElem?_set_ne (by omega),
-        getElem?_take h']
-    · by_cases h'' : m = n
-      · subst h''
-        rw [getElem?_set_eq (by simp; omega), getElem?_append_right, length_take,
-          Nat.min_eq_left (by omega), Nat.sub_self, getElem?_cons_zero]
-        rw [length_take]
-        exact Nat.min_le_left m l.length
-      · have h''' : n < m := by omega
-        rw [getElem?_set_ne (by omega), getElem?_append_right, length_take,
-          Nat.min_eq_left (by omega)]
-        · obtain ⟨k, rfl⟩ := Nat.exists_eq_add_of_lt h'''
-          have p : n + k + 1 - n = k + 1 := by omega
-          rw [p]
-          rw [getElem?_cons_succ, getElem?_drop]
-          congr 1
-          omega
-        · rw [length_take]
-          exact Nat.le_trans (Nat.min_le_left _ _) (by omega)
-  · rw [set_eq_of_length_le]
-    omega
+@[simp]
+theorem getElem?_take_of_succ {l : List α} {n : Nat} : (l.take (n + 1))[n]? = l[n]? :=
+  getElem?_take_of_lt (Nat.lt_succ_self n)
 
-theorem exists_of_set {n : Nat} {a' : α} {l : List α} (h : n < l.length) :
-    ∃ l₁ l₂, l = l₁ ++ l[n] :: l₂ ∧ l₁.length = n ∧ l.set n a' = l₁ ++ a' :: l₂ := by
-  refine ⟨l.take n, l.drop (n + 1), ⟨by simp, ⟨length_take_of_le (Nat.le_of_lt h), ?_⟩⟩⟩
-  simp [set_eq_take_append_cons_drop, h]
+@[simp] theorem drop_drop (n : Nat) : ∀ (m) (l : List α), drop n (drop m l) = drop (n + m) l
+  | m, [] => by simp
+  | 0, l => by simp
+  | m + 1, a :: l =>
+    calc
+      drop n (drop (m + 1) (a :: l)) = drop n (drop m l) := rfl
+      _ = drop (n + m) l := drop_drop n m l
+      _ = drop (n + (m + 1)) (a :: l) := rfl
 
-theorem drop_set_of_lt (a : α) {n m : Nat} (l : List α)
-    (hnm : n < m) : drop m (l.set n a) = l.drop m :=
-  ext_getElem? fun k => by simpa only [getElem?_drop] using getElem?_set_ne (by omega)
-
-theorem drop_take : ∀ (m n : Nat) (l : List α), drop n (take m l) = take (m - n) (drop n l)
+theorem take_drop : ∀ (m n : Nat) (l : List α), take n (drop m l) = drop m (take (m + n) l)
   | 0, _, _ => by simp
-  | _, 0, _ => by simp
   | _, _, [] => by simp
-  | m+1, n+1, h :: t => by
-    simp [take_succ_cons, drop_succ_cons, drop_take m n t]
-    congr 1
-    omega
+  | _+1, _, _ :: _ => by simpa [Nat.succ_add, take_succ_cons, drop_succ_cons] using take_drop ..
 
-theorem take_reverse {α} {xs : List α} (n : Nat) (h : n ≤ xs.length) :
-    xs.reverse.take n = (xs.drop (xs.length - n)).reverse := by
-  induction xs generalizing n <;>
-    simp only [reverse_cons, drop, reverse_nil, Nat.zero_sub, length, take_nil]
-  next xs_hd xs_tl xs_ih =>
-  cases Nat.lt_or_eq_of_le h with
-  | inl h' =>
-    have h' := Nat.le_of_succ_le_succ h'
-    rw [take_append_of_le_length, xs_ih _ h']
-    rw [show xs_tl.length + 1 - n = succ (xs_tl.length - n) from _, drop]
-    · rwa [succ_eq_add_one, Nat.sub_add_comm]
-    · rwa [length_reverse]
-  | inr h' =>
-    subst h'
-    rw [length, Nat.sub_self, drop]
-    suffices xs_tl.length + 1 = (xs_tl.reverse ++ [xs_hd]).length by
-      rw [this, take_length, reverse_cons]
-    rw [length_append, length_reverse]
-    rfl
+@[deprecated drop_drop (since := "2024-06-15")]
+theorem drop_add (m n) (l : List α) : drop (m + n) l = drop m (drop n l) := by
+  simp [drop_drop]
 
-@[deprecated (since := "2024-06-15")] abbrev reverse_take := @take_reverse
+@[simp]
+theorem tail_drop (l : List α) (n : Nat) : (l.drop n).tail = l.drop (n + 1) := by
+  induction l generalizing n with
+  | nil => simp
+  | cons hd tl hl =>
+    cases n
+    · simp
+    · simp [hl]
+
+@[simp]
+theorem drop_tail (l : List α) (n : Nat) : l.tail.drop n = l.drop (n + 1) := by
+  rw [← drop_drop, drop_one]
+
+@[simp]
+theorem drop_eq_nil_iff_le {l : List α} {k : Nat} : l.drop k = [] ↔ l.length ≤ k := by
+  refine ⟨fun h => ?_, drop_eq_nil_of_le⟩
+  induction k generalizing l with
+  | zero =>
+    simp only [drop] at h
+    simp [h]
+  | succ k hk =>
+    cases l
+    · simp
+    · simp only [drop] at h
+      simpa [Nat.succ_le_succ_iff] using hk h
+
+@[simp]
+theorem take_eq_nil_iff {l : List α} {k : Nat} : l.take k = [] ↔ k = 0 ∨ l = [] := by
+  cases l <;> cases k <;> simp [Nat.succ_ne_zero]
+
+theorem drop_eq_nil_of_eq_nil : ∀ {as : List α} {i}, as = [] → as.drop i = []
+  | _, _, rfl => drop_nil
+
+theorem ne_nil_of_drop_ne_nil {as : List α} {i : Nat} (h: as.drop i ≠ []) : as ≠ [] :=
+  mt drop_eq_nil_of_eq_nil h
+
+theorem take_eq_nil_of_eq_nil : ∀ {as : List α} {i}, as = [] → as.take i = []
+  | _, _, rfl => take_nil
+
+theorem ne_nil_of_take_ne_nil {as : List α} {i : Nat} (h : as.take i ≠ []) : as ≠ [] :=
+  mt take_eq_nil_of_eq_nil h
+
+theorem set_take {l : List α} {n m : Nat} {a : α} :
+    (l.set m a).take n = (l.take n).set m a := by
+  induction n generalizing l m with
+  | zero => simp
+  | succ _ hn =>
+    cases l with
+    | nil => simp
+    | cons hd tl => cases m <;> simp_all
+
+theorem drop_set {l : List α} {n m : Nat} {a : α} :
+    (l.set m a).drop n = if m < n then l.drop n else (l.drop n).set (m - n) a := by
+  induction n generalizing l m with
+  | zero => simp
+  | succ _ hn =>
+    cases l with
+    | nil => simp
+    | cons hd tl =>
+      cases m
+      · simp_all
+      · simp only [hn, set_cons_succ, drop_succ_cons, succ_lt_succ_iff]
+        congr 2
+        exact (Nat.add_sub_add_right ..).symm
+
+theorem set_drop {l : List α} {n m : Nat} {a : α} :
+    (l.drop n).set m a = (l.set (n + m) a).drop n := by
+  rw [drop_set, if_neg, add_sub_self_left n m]
+  exact (Nat.not_lt).2 (le_add_right n m)
+
+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]
+
+@[deprecated take_succ_cons (since := "2024-07-25")]
+theorem take_cons_succ : (a::as).take (i+1) = a :: as.take i := rfl
+
+@[deprecated take_of_length_le (since := "2024-07-25")]
+theorem take_all_of_le {n} {l : List α} (h : length l ≤ n) : take n l = l :=
+  take_of_length_le h
+
+theorem drop_left : ∀ l₁ l₂ : List α, drop (length l₁) (l₁ ++ l₂) = l₂
+  | [], _ => rfl
+  | _ :: l₁, l₂ => drop_left l₁ l₂
+
+@[simp]
+theorem drop_left' {l₁ l₂ : List α} {n} (h : length l₁ = n) : drop n (l₁ ++ l₂) = l₂ := by
+  rw [← h]; apply drop_left
+
+theorem take_left : ∀ l₁ l₂ : List α, take (length l₁) (l₁ ++ l₂) = l₁
+  | [], _ => rfl
+  | a :: l₁, l₂ => congrArg (cons a) (take_left l₁ l₂)
+
+@[simp]
+theorem take_left' {l₁ l₂ : List α} {n} (h : length l₁ = n) : take n (l₁ ++ l₂) = l₁ := by
+  rw [← h]; apply take_left
+
+theorem take_succ {l : List α} {n : Nat} : l.take (n + 1) = l.take n ++ l[n]?.toList := by
+  induction l generalizing n with
+  | nil =>
+    simp only [take_nil, Option.toList, getElem?_nil, append_nil]
+  | cons hd tl hl =>
+    cases n
+    · simp only [take, Option.toList, getElem?_cons_zero, nil_append]
+    · simp only [take, hl, getElem?_cons_succ, cons_append]
+
+@[deprecated (since := "2024-07-25")]
+theorem drop_sizeOf_le [SizeOf α] (l : List α) (n : Nat) : sizeOf (l.drop n) ≤ sizeOf l := by
+  induction l generalizing n with
+  | nil => rw [drop_nil]; apply Nat.le_refl
+  | cons _ _ lih =>
+    induction n with
+    | zero => apply Nat.le_refl
+    | succ n =>
+      exact Trans.trans (lih _) (Nat.le_add_left _ _)
+
+theorem dropLast_eq_take (l : List α) : l.dropLast = l.take (l.length - 1) := by
+  cases l with
+  | nil => simp [dropLast]
+  | cons x l =>
+    induction l generalizing x <;> simp_all [dropLast]
+
+@[simp] theorem map_take (f : α → β) :
+    ∀ (L : List α) (i : Nat), (L.take i).map f = (L.map f).take i
+  | [], i => by simp
+  | _, 0 => by simp
+  | h :: t, n + 1 => by dsimp; rw [map_take f t n]
+
+@[simp] theorem map_drop (f : α → β) :
+    ∀ (L : List α) (i : Nat), (L.drop i).map f = (L.map f).drop i
+  | [], i => by simp
+  | L, 0 => by simp
+  | h :: t, n + 1 => by
+    dsimp
+    rw [map_drop f t]
+
+/-! ### takeWhile and dropWhile -/
+
+theorem takeWhile_cons (p : α → Bool) (a : α) (l : List α) :
+    (a :: l).takeWhile p = if p a then a :: l.takeWhile p else [] := by
+  simp only [takeWhile]
+  by_cases h: p a <;> simp [h]
+
+@[simp] theorem takeWhile_cons_of_pos {p : α → Bool} {a : α} {l : List α} (h : p a) :
+    (a :: l).takeWhile p = a :: l.takeWhile p := by
+  simp [takeWhile_cons, h]
+
+@[simp] theorem takeWhile_cons_of_neg {p : α → Bool} {a : α} {l : List α} (h : ¬ p a) :
+    (a :: l).takeWhile p = [] := by
+  simp [takeWhile_cons, h]
+
+theorem dropWhile_cons :
+    (x :: xs : List α).dropWhile p = if p x then xs.dropWhile p else x :: xs := by
+  split <;> simp_all [dropWhile]
+
+@[simp] theorem dropWhile_cons_of_pos {a : α} {l : List α} (h : p a) :
+    (a :: l).dropWhile p = l.dropWhile p := by
+  simp [dropWhile_cons, h]
+
+@[simp] theorem dropWhile_cons_of_neg {a : α} {l : List α} (h : ¬ p a) :
+    (a :: l).dropWhile p = a :: l := by
+  simp [dropWhile_cons, h]
+
+theorem head?_takeWhile (p : α → Bool) (l : List α) : (l.takeWhile p).head? = l.head?.filter p := by
+  cases l with
+  | nil => rfl
+  | cons x xs =>
+    simp only [takeWhile_cons, head?_cons, Option.filter_some]
+    split <;> simp
+
+theorem head_takeWhile (p : α → Bool) (l : List α) (w) :
+    (l.takeWhile p).head w = l.head (by rintro rfl; simp_all) := by
+  cases l with
+  | nil => rfl
+  | cons x xs =>
+    simp only [takeWhile_cons, head_cons]
+    simp only [takeWhile_cons] at w
+    split <;> simp_all
+
+theorem head?_dropWhile_not (p : α → Bool) (l : List α) :
+    match (l.dropWhile p).head? with | some x => p x = false | none => True := by
+  induction l with
+  | nil => simp
+  | cons x xs ih =>
+    simp only [dropWhile_cons]
+    split <;> rename_i h <;> split at h <;> simp_all
+
+theorem head_dropWhile_not (p : α → Bool) (l : List α) (w) :
+    p ((l.dropWhile p).head w) = false := by
+  simpa [head?_eq_head, w] using head?_dropWhile_not p l
+
+theorem takeWhile_map (f : α → β) (p : β → Bool) (l : List α) :
+    (l.map f).takeWhile p = (l.takeWhile (p ∘ f)).map f := by
+  induction l with
+  | nil => rfl
+  | cons x xs ih =>
+    simp only [map_cons, takeWhile_cons]
+    split <;> simp_all
+
+theorem dropWhile_map (f : α → β) (p : β → Bool) (l : List α) :
+    (l.map f).dropWhile p = (l.dropWhile (p ∘ f)).map f := by
+  induction l with
+  | nil => rfl
+  | cons x xs ih =>
+    simp only [map_cons, dropWhile_cons]
+    split <;> simp_all
+
+theorem takeWhile_filterMap (f : α → Option β) (p : β → Bool) (l : List α) :
+    (l.filterMap f).takeWhile p = (l.takeWhile fun a => (f a).all p).filterMap f := by
+  induction l with
+  | nil => rfl
+  | cons x xs ih =>
+    simp only [filterMap_cons]
+    split <;> rename_i h
+    · simp only [takeWhile_cons, h]
+      split <;> simp_all
+    · simp [takeWhile_cons, h, ih]
+      split <;> simp_all [filterMap_cons]
+
+theorem dropWhile_filterMap (f : α → Option β) (p : β → Bool) (l : List α) :
+    (l.filterMap f).dropWhile p = (l.dropWhile fun a => (f a).all p).filterMap f := by
+  induction l with
+  | nil => rfl
+  | cons x xs ih =>
+    simp only [filterMap_cons]
+    split <;> rename_i h
+    · simp only [dropWhile_cons, h]
+      split <;> simp_all
+    · simp [dropWhile_cons, h, ih]
+      split <;> simp_all [filterMap_cons]
+
+theorem takeWhile_filter (p q : α → Bool) (l : List α) :
+    (l.filter p).takeWhile q = (l.takeWhile fun a => !p a || q a).filter p := by
+  simp [← filterMap_eq_filter, takeWhile_filterMap]
+
+theorem dropWhile_filter (p q : α → Bool) (l : List α) :
+    (l.filter p).dropWhile q = (l.dropWhile fun a => !p a || q a).filter p := by
+  simp [← filterMap_eq_filter, dropWhile_filterMap]
+
+@[simp] theorem takeWhile_append_dropWhile (p : α → Bool) :
+    ∀ (l : List α), takeWhile p l ++ dropWhile p l = l
+  | [] => rfl
+  | x :: xs => by simp [takeWhile, dropWhile]; cases p x <;> simp [takeWhile_append_dropWhile p xs]
+
+theorem takeWhile_append {xs ys : List α} :
+    (xs ++ ys).takeWhile p =
+      if (xs.takeWhile p).length = xs.length then xs ++ ys.takeWhile p else xs.takeWhile p := by
+  induction xs with
+  | nil => simp
+  | cons x xs ih =>
+    simp only [cons_append, takeWhile_cons]
+    split
+    · simp_all only [length_cons, add_one_inj]
+      split <;> rfl
+    · simp_all
+
+@[simp] theorem takeWhile_append_of_pos {p : α → Bool} {l₁ l₂ : List α} (h : ∀ a ∈ l₁, p a) :
+    (l₁ ++ l₂).takeWhile p = l₁ ++ l₂.takeWhile p := by
+  induction l₁ with
+  | nil => simp
+  | cons x xs ih => simp_all [takeWhile_cons]
+
+theorem dropWhile_append {xs ys : List α} :
+    (xs ++ ys).dropWhile p =
+      if (xs.dropWhile p).isEmpty then ys.dropWhile p else xs.dropWhile p ++ ys := by
+  induction xs with
+  | nil => simp
+  | cons h t ih =>
+    simp only [cons_append, dropWhile_cons]
+    split <;> simp_all
+
+@[simp] theorem dropWhile_append_of_pos {p : α → Bool} {l₁ l₂ : List α} (h : ∀ a ∈ l₁, p a) :
+    (l₁ ++ l₂).dropWhile p = l₂.dropWhile p := by
+  induction l₁ with
+  | nil => simp
+  | cons x xs ih => simp_all [dropWhile_cons]
+
+@[simp] theorem takeWhile_replicate_eq_filter (p : α → Bool) :
+    (replicate n a).takeWhile p = (replicate n a).filter p := by
+  induction n with
+  | zero => simp
+  | succ n ih =>
+    simp only [replicate_succ, takeWhile_cons]
+    split <;> simp_all
+
+theorem takeWhile_replicate (p : α → Bool) :
+    (replicate n a).takeWhile p = if p a then replicate n a else [] := by
+  rw [takeWhile_replicate_eq_filter, filter_replicate]
+
+@[simp] theorem dropWhile_replicate_eq_filter_not (p : α → Bool) :
+    (replicate n a).dropWhile p = (replicate n a).filter (fun a => !p a) := by
+  induction n with
+  | zero => simp
+  | succ n ih =>
+    simp only [replicate_succ, dropWhile_cons]
+    split <;> simp_all
+
+theorem dropWhile_replicate (p : α → Bool) :
+    (replicate n a).dropWhile p = if p a then [] else replicate n a := by
+  simp only [dropWhile_replicate_eq_filter_not, filter_replicate]
+  split <;> simp_all
+
+theorem take_takeWhile {l : List α} (p : α → Bool) n :
+    (l.takeWhile p).take n = (l.take n).takeWhile p := by
+  induction l generalizing n with
+  | nil => simp
+  | cons x xs ih =>
+    by_cases h : p x <;> cases n <;> simp [takeWhile_cons, h, ih, take_succ_cons]
+
+@[simp] theorem all_takeWhile {l : List α} : (l.takeWhile p).all p = true := by
+  induction l with
+  | nil => rfl
+  | cons h t ih => by_cases p h <;> simp_all
+
+@[simp] theorem any_dropWhile {l : List α} :
+    (l.dropWhile p).any (fun x => !p x) = !l.all p := by
+  induction l with
+  | nil => rfl
+  | cons h t ih => by_cases p h <;> simp_all
+
+/-! ### splitAt -/
+
+@[simp] theorem splitAt_eq (n : Nat) (l : List α) : splitAt n l = (l.take n, l.drop n) := by
+  rw [splitAt, splitAt_go, reverse_nil, nil_append]
+  split <;> simp_all [take_of_length_le, drop_of_length_le]
 
 /-! ### rotateLeft -/
 
-@[simp] theorem rotateLeft_replicate (n) (a : α) : rotateLeft (replicate m a) n = replicate m a := by
-  cases n with
-  | zero => simp
-  | succ n =>
-    suffices 1 < m → m - (n + 1) % m + min ((n + 1) % m) m = m by
-      simpa [rotateLeft]
-    intro h
-    rw [Nat.min_eq_left (Nat.le_of_lt (Nat.mod_lt _ (by omega)))]
-    have : (n + 1) % m < m := Nat.mod_lt _ (by omega)
-    omega
+@[simp] theorem rotateLeft_zero (l : List α) : rotateLeft l 0 = l := by
+  simp [rotateLeft]
+
+-- TODO Batteries defines its own `getElem?_rotate`, which we need to adapt.
+-- TODO Prove `map_rotateLeft`, using `ext` and `getElem?_rotateLeft`.
 
 /-! ### rotateRight -/
 
-@[simp] theorem rotateRight_replicate (n) (a : α) : rotateRight (replicate m a) n = replicate m a := by
-  cases n with
-  | zero => simp
-  | succ n =>
-    suffices 1 < m → m - (m - (n + 1) % m) + min (m - (n + 1) % m) m = m by
-      simpa [rotateRight]
-    intro h
-    have : (n + 1) % m < m := Nat.mod_lt _ (by omega)
-    rw [Nat.min_eq_left (by omega)]
-    omega
+@[simp] theorem rotateRight_zero (l : List α) : rotateRight l 0 = l := by
+  simp [rotateRight]
 
-/-! ### zipWith -/
-
-@[simp] theorem length_zipWith (f : α → β → γ) (l₁ l₂) :
-    length (zipWith f l₁ l₂) = min (length l₁) (length l₂) := by
-  induction l₁ generalizing l₂ <;> cases l₂ <;>
-    simp_all [succ_min_succ, Nat.zero_min, Nat.min_zero]
-
-theorem zipWith_eq_zipWith_take_min : ∀ (l₁ : List α) (l₂ : List β),
-    zipWith f l₁ l₂ = zipWith f (l₁.take (min l₁.length l₂.length)) (l₂.take (min l₁.length l₂.length))
-  | [], _ => by simp
-  | _, [] => by simp
-  | a :: l₁, b :: l₂ => by simp [succ_min_succ, zipWith_eq_zipWith_take_min l₁ l₂]
-
-@[simp] theorem zipWith_replicate {a : α} {b : β} {m n : Nat} :
-    zipWith f (replicate m a) (replicate n b) = replicate (min m n) (f a b) := by
-  rw [zipWith_eq_zipWith_take_min]
-  simp
-
-/-! ### zip -/
-
-@[simp] theorem length_zip (l₁ : List α) (l₂ : List β) :
-    length (zip l₁ l₂) = min (length l₁) (length l₂) := by
-  simp [zip]
-
-theorem zip_eq_zip_take_min : ∀ (l₁ : List α) (l₂ : List β),
-    zip l₁ l₂ = zip (l₁.take (min l₁.length l₂.length)) (l₂.take (min l₁.length l₂.length))
-  | [], _ => by simp
-  | _, [] => by simp
-  | a :: l₁, b :: l₂ => by simp [succ_min_succ, zip_eq_zip_take_min l₁ l₂]
-
-@[simp] theorem zip_replicate {a : α} {b : β} {m n : Nat} :
-    zip (replicate m a) (replicate n b) = replicate (min m n) (a, b) := by
-  rw [zip_eq_zip_take_min]
-  simp
-
-/-! ### minimum? -/
-
--- A specialization of `minimum?_eq_some_iff` to Nat.
-theorem minimum?_eq_some_iff' {xs : List Nat} :
-    xs.minimum? = some a ↔ (a ∈ xs ∧ ∀ b ∈ xs, a ≤ b) :=
-  minimum?_eq_some_iff
-    (le_refl := Nat.le_refl)
-    (min_eq_or := fun _ _ => by omega)
-    (le_min_iff := fun _ _ _ => by omega)
-
--- This could be generalized,
--- but will first require further work on order typeclasses in the core repository.
-theorem minimum?_cons' {a : Nat} {l : List Nat} :
-    (a :: l).minimum? = some (match l.minimum? with
-    | none => a
-    | some m => min a m) := by
-  rw [minimum?_eq_some_iff']
-  split <;> rename_i h m
-  · simp_all
-  · rw [minimum?_eq_some_iff'] at m
-    obtain ⟨m, le⟩ := m
-    rw [Nat.min_def]
-    constructor
-    · split
-      · exact mem_cons_self a l
-      · exact mem_cons_of_mem a m
-    · intro b m
-      cases List.mem_cons.1 m with
-      | inl => split <;> omega
-      | inr h =>
-        specialize le b h
-        split <;> omega
-
-/-! ### maximum? -/
-
--- A specialization of `maximum?_eq_some_iff` to Nat.
-theorem maximum?_eq_some_iff' {xs : List Nat} :
-    xs.maximum? = some a ↔ (a ∈ xs ∧ ∀ b ∈ xs, b ≤ a) :=
-  maximum?_eq_some_iff
-    (le_refl := Nat.le_refl)
-    (max_eq_or := fun _ _ => by omega)
-    (max_le_iff := fun _ _ _ => by omega)
-
--- This could be generalized,
--- but will first require further work on order typeclasses in the core repository.
-theorem maximum?_cons' {a : Nat} {l : List Nat} :
-    (a :: l).maximum? = some (match l.maximum? with
-    | none => a
-    | some m => max a m) := by
-  rw [maximum?_eq_some_iff']
-  split <;> rename_i h m
-  · simp_all
-  · rw [maximum?_eq_some_iff'] at m
-    obtain ⟨m, le⟩ := m
-    rw [Nat.max_def]
-    constructor
-    · split
-      · exact mem_cons_of_mem a m
-      · exact mem_cons_self a l
-    · intro b m
-      cases List.mem_cons.1 m with
-      | inl => split <;> omega
-      | inr h =>
-        specialize le b h
-        split <;> omega
+-- TODO Batteries defines its own `getElem?_rotate`, which we need to adapt.
+-- TODO Prove `map_rotateRight`, using `ext` and `getElem?_rotateRight`.
 
 end List

src/Init/Data/List/Zip.lean

@@ -0,0 +1,363 @@
+/-
+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.TakeDrop
+
+/-!
+# Lemmas about `List.zip`, `List.zipWith`, `List.zipWithAll`, and `List.unzip`.
+-/
+
+namespace List
+
+open Nat
+
+/-! ## Zippers -/
+
+/-! ### zip -/
+
+theorem zip_map (f : α → γ) (g : β → δ) :
+    ∀ (l₁ : List α) (l₂ : List β), zip (l₁.map f) (l₂.map g) = (zip l₁ l₂).map (Prod.map f g)
+  | [], l₂ => rfl
+  | l₁, [] => by simp only [map, zip_nil_right]
+  | a :: l₁, b :: l₂ => by
+    simp only [map, zip_cons_cons, zip_map, Prod.map]; constructor
+
+theorem zip_map_left (f : α → γ) (l₁ : List α) (l₂ : List β) :
+    zip (l₁.map f) l₂ = (zip l₁ l₂).map (Prod.map f id) := by rw [← zip_map, map_id]
+
+theorem zip_map_right (f : β → γ) (l₁ : List α) (l₂ : List β) :
+    zip l₁ (l₂.map f) = (zip l₁ l₂).map (Prod.map id f) := by rw [← zip_map, map_id]
+
+theorem zip_append :
+    ∀ {l₁ r₁ : List α} {l₂ r₂ : List β} (_h : length l₁ = length l₂),
+      zip (l₁ ++ r₁) (l₂ ++ r₂) = zip l₁ l₂ ++ zip r₁ r₂
+  | [], r₁, l₂, r₂, h => by simp only [eq_nil_of_length_eq_zero h.symm]; rfl
+  | l₁, r₁, [], r₂, h => by simp only [eq_nil_of_length_eq_zero h]; rfl
+  | a :: l₁, r₁, b :: l₂, r₂, h => by
+    simp only [cons_append, zip_cons_cons, zip_append (Nat.succ.inj h)]
+
+theorem zip_map' (f : α → β) (g : α → γ) :
+    ∀ l : List α, zip (l.map f) (l.map g) = l.map fun a => (f a, g a)
+  | [] => rfl
+  | a :: l => by simp only [map, zip_cons_cons, zip_map']
+
+theorem of_mem_zip {a b} : ∀ {l₁ : List α} {l₂ : List β}, (a, b) ∈ zip l₁ l₂ → a ∈ l₁ ∧ b ∈ l₂
+  | _ :: l₁, _ :: l₂, h => by
+    cases h
+    case head => simp
+    case tail h =>
+    · have := of_mem_zip h
+      exact ⟨Mem.tail _ this.1, Mem.tail _ this.2⟩
+
+@[deprecated of_mem_zip (since := "2024-07-28")] abbrev mem_zip := @of_mem_zip
+
+theorem map_fst_zip :
+    ∀ (l₁ : List α) (l₂ : List β), l₁.length ≤ l₂.length → map Prod.fst (zip l₁ l₂) = l₁
+  | [], bs, _ => rfl
+  | _ :: as, _ :: bs, h => by
+    simp [Nat.succ_le_succ_iff] at h
+    show _ :: map Prod.fst (zip as bs) = _ :: as
+    rw [map_fst_zip as bs h]
+  | a :: as, [], h => by simp at h
+
+theorem map_snd_zip :
+    ∀ (l₁ : List α) (l₂ : List β), l₂.length ≤ l₁.length → map Prod.snd (zip l₁ l₂) = l₂
+  | _, [], _ => by
+    rw [zip_nil_right]
+    rfl
+  | [], b :: bs, h => by simp at h
+  | a :: as, b :: bs, h => by
+    simp [Nat.succ_le_succ_iff] at h
+    show _ :: map Prod.snd (zip as bs) = _ :: bs
+    rw [map_snd_zip as bs h]
+
+theorem map_prod_left_eq_zip {l : List α} (f : α → β) :
+    (l.map fun x => (x, f x)) = l.zip (l.map f) := by
+  rw [← zip_map']
+  congr
+  exact map_id _
+
+theorem map_prod_right_eq_zip {l : List α} (f : α → β) :
+    (l.map fun x => (f x, x)) = (l.map f).zip l := by
+  rw [← zip_map']
+  congr
+  exact map_id _
+
+/-- See also `List.zip_replicate` in `Init.Data.List.TakeDrop` for a generalization with different lengths. -/
+@[simp] theorem zip_replicate' {a : α} {b : β} {n : Nat} :
+    zip (replicate n a) (replicate n b) = replicate n (a, b) := by
+  induction n with
+  | zero => rfl
+  | succ n ih => simp [replicate_succ, ih]
+
+/-! ### zipWith -/
+
+theorem zipWith_comm (f : α → β → γ) :
+    ∀ (la : List α) (lb : List β), zipWith f la lb = zipWith (fun b a => f a b) lb la
+  | [], _ => List.zipWith_nil_right.symm
+  | _ :: _, [] => rfl
+  | _ :: as, _ :: bs => congrArg _ (zipWith_comm f as bs)
+
+theorem zipWith_comm_of_comm (f : α → α → β) (comm : ∀ x y : α, f x y = f y x) (l l' : List α) :
+    zipWith f l l' = zipWith f l' l := by
+  rw [zipWith_comm]
+  simp only [comm]
+
+@[simp]
+theorem zipWith_same (f : α → α → δ) : ∀ l : List α, zipWith f l l = l.map fun a => f a a
+  | [] => rfl
+  | _ :: xs => congrArg _ (zipWith_same f xs)
+
+/--
+See also `getElem?_zipWith'` for a variant
+using `Option.map` and `Option.bind` rather than a `match`.
+-/
+theorem getElem?_zipWith {f : α → β → γ} {i : Nat} :
+    (List.zipWith f as bs)[i]? = match as[i]?, bs[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
+
+/-- Variant of `getElem?_zipWith` using `Option.map` and `Option.bind` rather than a `match`. -/
+theorem getElem?_zipWith' {f : α → β → γ} {i : Nat} :
+    (zipWith f l₁ l₂)[i]? = (l₁[i]?.map f).bind fun g => l₂[i]?.map g := by
+  induction l₁ generalizing l₂ i with
+  | nil => rw [zipWith] <;> simp
+  | cons head tail =>
+    cases l₂
+    · simp
+    · cases i <;> simp_all
+
+theorem getElem?_zipWith_eq_some (f : α → β → γ) (l₁ : List α) (l₂ : List β) (z : γ) (i : Nat) :
+    (zipWith f l₁ l₂)[i]? = some z ↔
+      ∃ x y, l₁[i]? = some x ∧ l₂[i]? = some y ∧ f x y = z := by
+  induction l₁ generalizing l₂ i
+  · simp
+  · cases l₂ <;> cases i <;> simp_all
+
+theorem getElem?_zip_eq_some (l₁ : List α) (l₂ : List β) (z : α × β) (i : Nat) :
+    (zip l₁ l₂)[i]? = some z ↔ l₁[i]? = some z.1 ∧ l₂[i]? = some z.2 := by
+  cases z
+  rw [zip, getElem?_zipWith_eq_some]; constructor
+  · rintro ⟨x, y, h₀, h₁, h₂⟩
+    simpa [h₀, h₁] using h₂
+  · rintro ⟨h₀, h₁⟩
+    exact ⟨_, _, h₀, h₁, rfl⟩
+
+@[deprecated getElem?_zipWith (since := "2024-06-12")]
+theorem get?_zipWith {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
+  simp [getElem?_zipWith]
+
+set_option linter.deprecated false in
+@[deprecated getElem?_zipWith (since := "2024-06-07")] abbrev zipWith_get? := @get?_zipWith
+
+theorem head?_zipWith {f : α → β → γ} :
+    (List.zipWith f as bs).head? = match as.head?, bs.head? with
+      | some a, some b => some (f a b) | _, _ => none := by
+  simp [head?_eq_getElem?, getElem?_zipWith]
+
+theorem head_zipWith {f : α → β → γ} (h):
+    (List.zipWith f as bs).head h = f (as.head (by rintro rfl; simp_all)) (bs.head (by rintro rfl; simp_all)) := by
+  apply Option.some.inj
+  rw [← head?_eq_head, head?_zipWith, head?_eq_head, head?_eq_head]
+
+@[simp]
+theorem zipWith_map {μ} (f : γ → δ → μ) (g : α → γ) (h : β → δ) (l₁ : List α) (l₂ : List β) :
+    zipWith f (l₁.map g) (l₂.map h) = zipWith (fun a b => f (g a) (h b)) l₁ l₂ := by
+  induction l₁ generalizing l₂ <;> cases l₂ <;> simp_all
+
+theorem zipWith_map_left (l₁ : List α) (l₂ : List β) (f : α → α') (g : α' → β → γ) :
+    zipWith g (l₁.map f) l₂ = zipWith (fun a b => g (f a) b) l₁ l₂ := by
+  induction l₁ generalizing l₂ <;> cases l₂ <;> simp_all
+
+theorem zipWith_map_right (l₁ : List α) (l₂ : List β) (f : β → β') (g : α → β' → γ) :
+    zipWith g l₁ (l₂.map f) = zipWith (fun a b => g a (f b)) l₁ l₂ := by
+  induction l₁ generalizing l₂ <;> cases l₂ <;> simp_all
+
+theorem zipWith_foldr_eq_zip_foldr {f : α → β → γ} (i : δ):
+    (zipWith f l₁ l₂).foldr g i = (zip l₁ l₂).foldr (fun p r => g (f p.1 p.2) r) i := by
+  induction l₁ generalizing l₂ <;> cases l₂ <;> simp_all
+
+theorem zipWith_foldl_eq_zip_foldl {f : α → β → γ} (i : δ):
+    (zipWith f l₁ l₂).foldl g i = (zip l₁ l₂).foldl (fun r p => g r (f p.1 p.2)) i := by
+  induction l₁ generalizing i l₂ <;> cases l₂ <;> simp_all
+
+@[simp]
+theorem zipWith_eq_nil_iff {f : α → β → γ} {l l'} : zipWith f l l' = [] ↔ l = [] ∨ l' = [] := by
+  cases l <;> cases l' <;> simp
+
+theorem map_zipWith {δ : Type _} (f : α → β) (g : γ → δ → α) (l : List γ) (l' : List δ) :
+    map f (zipWith g l l') = zipWith (fun x y => f (g x y)) l l' := by
+  induction l generalizing l' with
+  | nil => simp
+  | cons hd tl hl =>
+    · cases l'
+      · simp
+      · simp [hl]
+
+theorem take_zipWith : (zipWith f l l').take n = zipWith f (l.take n) (l'.take n) := by
+  induction l generalizing l' n with
+  | nil => simp
+  | cons hd tl hl =>
+    cases l'
+    · simp
+    · cases n
+      · simp
+      · simp [hl]
+
+@[deprecated take_zipWith (since := "2024-07-26")] abbrev zipWith_distrib_take := @take_zipWith
+
+theorem drop_zipWith : (zipWith f l l').drop n = zipWith f (l.drop n) (l'.drop n) := by
+  induction l generalizing l' n with
+  | nil => simp
+  | cons hd tl hl =>
+    · cases l'
+      · simp
+      · cases n
+        · simp
+        · simp [hl]
+
+@[deprecated drop_zipWith (since := "2024-07-26")] abbrev zipWith_distrib_drop := @drop_zipWith
+
+theorem tail_zipWith : (zipWith f l l').tail = zipWith f l.tail l'.tail := by
+  rw [← drop_one]; simp [drop_zipWith]
+
+@[deprecated tail_zipWith (since := "2024-07-28")] abbrev zipWith_distrib_tail := @tail_zipWith
+
+theorem zipWith_append (f : α → β → γ) (l la : List α) (l' lb : List β)
+    (h : l.length = l'.length) :
+    zipWith f (l ++ la) (l' ++ lb) = zipWith f l l' ++ zipWith f la lb := by
+  induction l generalizing l' with
+  | nil =>
+    have : l' = [] := eq_nil_of_length_eq_zero (by simpa using h.symm)
+    simp [this]
+  | cons hl tl ih =>
+    cases l' with
+    | nil => simp at h
+    | cons head tail =>
+      simp only [length_cons, Nat.succ.injEq] at h
+      simp [ih _ h]
+
+/-- See also `List.zipWith_replicate` in `Init.Data.List.TakeDrop` for a generalization with different lengths. -/
+@[simp] theorem zipWith_replicate' {a : α} {b : β} {n : Nat} :
+    zipWith f (replicate n a) (replicate n b) = replicate n (f a b) := by
+  induction n with
+  | zero => rfl
+  | succ n ih => simp [replicate_succ, ih]
+
+/-! ### zipWithAll -/
+
+theorem getElem?_zipWithAll {f : Option α → Option β → γ} {i : Nat} :
+    (zipWithAll f as bs)[i]? = match as[i]?, bs[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
+
+@[deprecated getElem?_zipWithAll (since := "2024-06-12")]
+theorem get?_zipWithAll {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
+  simp [getElem?_zipWithAll]
+
+set_option linter.deprecated false in
+@[deprecated getElem?_zipWithAll (since := "2024-06-07")] abbrev zipWithAll_get? := @get?_zipWithAll
+
+theorem head?_zipWithAll {f : Option α → Option β → γ} :
+    (zipWithAll f as bs).head? = match as.head?, bs.head? with
+      | none, none => .none | a?, b? => some (f a? b?) := by
+  simp [head?_eq_getElem?, getElem?_zipWithAll]
+
+theorem head_zipWithAll {f : Option α → Option β → γ} (h) :
+    (zipWithAll f as bs).head h = f as.head? bs.head? := by
+  apply Option.some.inj
+  rw [← head?_eq_head, head?_zipWithAll]
+  split <;> simp_all
+
+theorem zipWithAll_map {μ} (f : Option γ → Option δ → μ) (g : α → γ) (h : β → δ) (l₁ : List α) (l₂ : List β) :
+    zipWithAll f (l₁.map g) (l₂.map h) = zipWithAll (fun a b => f (g <$> a) (h <$> b)) l₁ l₂ := by
+  induction l₁ generalizing l₂ <;> cases l₂ <;> simp_all
+
+theorem zipWithAll_map_left (l₁ : List α) (l₂ : List β) (f : α → α') (g : Option α' → Option β → γ) :
+    zipWithAll g (l₁.map f) l₂ = zipWithAll (fun a b => g (f <$> a) b) l₁ l₂ := by
+  induction l₁ generalizing l₂ <;> cases l₂ <;> simp_all
+
+theorem zipWithAll_map_right (l₁ : List α) (l₂ : List β) (f : β → β') (g : Option α → Option β' → γ) :
+    zipWithAll g l₁ (l₂.map f) = zipWithAll (fun a b => g a (f <$> b)) l₁ l₂ := by
+  induction l₁ generalizing l₂ <;> cases l₂ <;> simp_all
+
+theorem map_zipWithAll {δ : Type _} (f : α → β) (g : Option γ → Option δ → α) (l : List γ) (l' : List δ) :
+    map f (zipWithAll g l l') = zipWithAll (fun x y => f (g x y)) l l' := by
+  induction l generalizing l' with
+  | nil => simp
+  | cons hd tl hl =>
+    cases l' <;> simp_all
+
+@[simp] theorem zipWithAll_replicate {a : α} {b : β} {n : Nat} :
+    zipWithAll f (replicate n a) (replicate n b) = replicate n (f a b) := by
+  induction n with
+  | zero => rfl
+  | succ n ih => simp [replicate_succ, ih]
+
+/-! ### unzip -/
+
+@[simp] theorem unzip_fst : (unzip l).fst = l.map Prod.fst := by
+  induction l <;> simp_all
+
+@[simp] theorem unzip_snd : (unzip l).snd = l.map Prod.snd := by
+  induction l <;> simp_all
+
+@[deprecated unzip_fst (since := "2024-07-28")] abbrev unzip_left := @unzip_fst
+@[deprecated unzip_snd (since := "2024-07-28")] abbrev unzip_right := @unzip_snd
+
+theorem unzip_eq_map : ∀ l : List (α × β), unzip l = (l.map Prod.fst, l.map Prod.snd)
+  | [] => rfl
+  | (a, b) :: l => by simp only [unzip_cons, map_cons, unzip_eq_map l]
+
+theorem zip_unzip : ∀ l : List (α × β), zip (unzip l).1 (unzip l).2 = l
+  | [] => rfl
+  | (a, b) :: l => by simp only [unzip_cons, zip_cons_cons, zip_unzip l]
+
+theorem unzip_zip_left :
+    ∀ {l₁ : List α} {l₂ : List β}, length l₁ ≤ length l₂ → (unzip (zip l₁ l₂)).1 = l₁
+  | [], l₂, _ => rfl
+  | l₁, [], h => by rw [eq_nil_of_length_eq_zero (Nat.eq_zero_of_le_zero h)]; rfl
+  | a :: l₁, b :: l₂, h => by
+    simp only [zip_cons_cons, unzip_cons, unzip_zip_left (le_of_succ_le_succ h)]
+
+theorem unzip_zip_right :
+    ∀ {l₁ : List α} {l₂ : List β}, length l₂ ≤ length l₁ → (unzip (zip l₁ l₂)).2 = l₂
+  | [], l₂, _ => by simp_all
+  | l₁, [], _ => by simp
+  | a :: l₁, b :: l₂, h => by
+    simp only [zip_cons_cons, unzip_cons, unzip_zip_right (le_of_succ_le_succ h)]
+
+theorem unzip_zip {l₁ : List α} {l₂ : List β} (h : length l₁ = length l₂) :
+    unzip (zip l₁ l₂) = (l₁, l₂) := by
+  ext
+  · rw [unzip_zip_left (Nat.le_of_eq h)]
+  · rw [unzip_zip_right (Nat.le_of_eq h.symm)]
+
+theorem zip_of_prod {l : List α} {l' : List β} {lp : List (α × β)} (hl : lp.map Prod.fst = l)
+    (hr : lp.map Prod.snd = l') : lp = l.zip l' := by
+  rw [← hl, ← hr, ← zip_unzip lp, ← unzip_fst, ← unzip_snd, zip_unzip, zip_unzip]
+
+@[simp] theorem unzip_replicate {n : Nat} {a : α} {b : β} :
+    unzip (replicate n (a, b)) = (replicate n a, replicate n b) := by
+  ext1 <;> simp

src/Init/Data/Nat/Basic.lean

@@ -102,6 +102,13 @@ def blt (a b : Nat) : Bool :=
 attribute [simp] Nat.zero_le
 attribute [simp] Nat.not_lt_zero
 
+theorem and_forall_add_one {p : Nat → Prop} : p 0 ∧ (∀ n, p (n + 1)) ↔ ∀ n, p n :=
+  ⟨fun h n => Nat.casesOn n h.1 h.2, fun h => ⟨h _, fun _ => h _⟩⟩
+
+theorem or_exists_add_one : p 0 ∨ (Exists fun n => p (n + 1)) ↔ Exists p :=
+  ⟨fun h => h.elim (fun h0 => ⟨0, h0⟩) fun ⟨n, hn⟩ => ⟨n + 1, hn⟩,
+    fun ⟨n, h⟩ => match n with | 0 => Or.inl h | n+1 => Or.inr ⟨n, h⟩⟩
+
 /-! # Helper "packing" theorems -/
 
 @[simp] theorem zero_eq : Nat.zero = 0 := rfl
@@ -388,11 +395,11 @@ theorem le_or_eq_of_le_succ {m n : Nat} (h : m ≤ succ n) : m ≤ n ∨ m = suc
 theorem le_or_eq_of_le_add_one {m n : Nat} (h : m ≤ n + 1) : m ≤ n ∨ m = n + 1 :=
   le_or_eq_of_le_succ h
 
-theorem le_add_right : ∀ (n k : Nat), n ≤ n + k
+@[simp] theorem le_add_right : ∀ (n k : Nat), n ≤ n + k
   | n, 0   => Nat.le_refl n
   | n, k+1 => le_succ_of_le (le_add_right n k)
 
-theorem le_add_left (n m : Nat): n ≤ m + n :=
+@[simp] theorem le_add_left (n m : Nat): n ≤ m + n :=
   Nat.add_comm n m ▸ le_add_right n m
 
 theorem le_of_add_right_le {n m k : Nat} (h : n + k ≤ m) : n ≤ m :=
@@ -528,7 +535,7 @@ 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 :=
+@[simp] 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 -/
@@ -1080,6 +1087,10 @@ protected theorem sub_eq_iff_eq_add {c : Nat} (h : b ≤ a) : a - b = c ↔ a =
 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]
 
+protected theorem sub_one_sub_lt_of_lt (h : a < b) : b - 1 - a < b := by
+  rw [← Nat.sub_add_eq]
+  exact sub_lt (zero_lt_of_lt h) (Nat.lt_add_right a Nat.one_pos)
+
 /-! ## Mul sub distrib -/
 
 theorem pred_mul (n m : Nat) : pred n * m = n * m - m := by

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

@@ -265,8 +265,8 @@ theorem testBit_two_pow_add_gt {i j : Nat} (j_lt_i : j < i) (x : Nat) :
       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 [x_eq, Nat.lt_add_right_iff_pos]
+        exact 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]

src/Init/Data/Nat/Div.lean

@@ -203,6 +203,10 @@ theorem mod_add_div (m k : Nat) : m % k + k * (m / k) = m := by
   | 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]
 
+theorem mod_def (m k : Nat) : m % k = m - k * (m / k) := by
+  rw [Nat.sub_eq_of_eq_add]
+  apply (Nat.mod_add_div _ _).symm
+
 @[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

src/Init/Data/Nat/Gcd.lean

@@ -46,6 +46,9 @@ theorem gcd_succ (x y : Nat) : gcd (succ x) y = gcd (y % succ x) (succ x) := by
 theorem gcd_add_one (x y : Nat) : gcd (x + 1) y = gcd (y % (x + 1)) (x + 1) := by
   rw [gcd]; rfl
 
+theorem gcd_def (x y : Nat) : gcd x y = if x = 0 then y else gcd (y % x) x := by
+  cases x <;> simp [Nat.gcd_add_one]
+
 @[simp] theorem gcd_one_left (n : Nat) : gcd 1 n = 1 := by
   rw [gcd_succ, mod_one]
   rfl

src/Init/Data/Nat/Lemmas.lean

@@ -19,6 +19,14 @@ and later these lemmas should be organised into other files more systematically.
 -/
 
 namespace Nat
+
+@[deprecated and_forall_add_one (since := "2024-07-30")] abbrev and_forall_succ := @and_forall_add_one
+@[deprecated or_exists_add_one (since := "2024-07-30")] abbrev or_exists_succ := @or_exists_add_one
+
+@[simp] theorem exists_ne_zero {P : Nat → Prop} : (∃ n, ¬ n = 0 ∧ P n) ↔ ∃ n, P (n + 1) :=
+  ⟨fun ⟨n, h, w⟩ => by cases n with | zero => simp at h | succ n => exact ⟨n, w⟩,
+    fun ⟨n, w⟩ => ⟨n + 1, by simp, w⟩⟩
+
 /-! ## add -/
 
 protected theorem add_add_add_comm (a b c d : Nat) : (a + b) + (c + d) = (a + c) + (b + d) := by
@@ -36,13 +44,13 @@ protected theorem eq_zero_of_add_eq_zero_right (h : n + m = 0) : n = 0 :=
 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 :=
+@[simp] 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 :=
+@[simp] 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 :=
+@[simp] 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
@@ -52,10 +60,10 @@ protected theorem lt_of_add_lt_add_right : ∀ {n : Nat}, k + n < m + n → k <
 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 :=
+@[simp] 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 :=
+@[simp] 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) :
@@ -75,10 +83,10 @@ protected theorem pos_of_lt_add_right (h : n < n + k) : 0 < k :=
 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 :=
+@[simp] 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 :=
+@[simp] 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 :=

src/Init/Data/Nat/Linear.lean

@@ -173,13 +173,13 @@ instance : LawfulBEq PolyCnstr where
   eq_of_beq {a b} h := by
     cases a; rename_i eq₁ lhs₁ rhs₁
     cases b; rename_i eq₂ lhs₂ rhs₂
-    have h : eq₁ == eq₂ && lhs₁ == lhs₂ && rhs₁ == rhs₂ := h
+    have h : eq₁ == eq₂ && (lhs₁ == lhs₂ && rhs₁ == rhs₂) := h
     simp at h
-    have ⟨⟨h₁, h₂⟩, h₃⟩ := h
+    have ⟨h₁, h₂, h₃⟩ := h
     rw [h₁, h₂, h₃]
   rfl {a} := by
     cases a; rename_i eq lhs rhs
-    show (eq == eq && lhs == lhs && rhs == rhs) = true
+    show (eq == eq && (lhs == lhs && rhs == rhs)) = true
     simp [LawfulBEq.rfl]
 
 def PolyCnstr.mul (k : Nat) (c : PolyCnstr) : PolyCnstr :=

src/Init/Data/Option/Basic.lean

@@ -212,6 +212,9 @@ instance (α) [BEq α] [LawfulBEq α] : LawfulBEq (Option α) where
 @[simp] theorem all_none : Option.all p none = true := rfl
 @[simp] theorem all_some : Option.all p (some x) = p x := rfl
 
+@[simp] theorem any_none : Option.any p none = false := rfl
+@[simp] theorem any_some : Option.any 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)

src/Init/Data/Option/Lemmas.lean

@@ -167,6 +167,9 @@ theorem isSome_map {x : Option α} : (f <$> x).isSome = x.isSome := by
 @[simp] theorem isSome_map' {x : Option α} : (x.map f).isSome = x.isSome := by
   cases x <;> simp
 
+@[simp] theorem isNone_map' {x : Option α} : (x.map f).isNone = x.isNone := by
+  cases x <;> simp
+
 theorem map_eq_none : f <$> x = none ↔ x = none := map_eq_none'
 
 theorem map_eq_bind {x : Option α} : x.map f = x.bind (some ∘ f) := by
@@ -190,9 +193,27 @@ theorem comp_map (h : β → γ) (g : α → β) (x : Option α) : x.map (h ∘
 
 theorem mem_map_of_mem (g : α → β) (h : a ∈ x) : g a ∈ Option.map g x := h.symm ▸ map_some' ..
 
+@[simp] theorem map_if {f : α → β} [Decidable c] :
+     (if c then some a else none).map f = if c then some (f a) else none := by
+  split <;> rfl
+
+@[simp] theorem map_dif {f : α → β} [Decidable c] {a : c → α} :
+     (if h : c then some (a h) else none).map f = if h : c then some (f (a h)) else none := by
+  split <;> rfl
+
 @[simp] theorem filter_none (p : α → Bool) : none.filter p = none := rfl
 theorem filter_some : Option.filter p (some a) = if p a then some a else none := rfl
 
+@[simp] theorem all_guard (p : α → Prop) [DecidablePred p] (a : α) :
+    Option.all q (guard p a) = (!p a || q a) := by
+  simp only [guard]
+  split <;> simp_all
+
+@[simp] theorem any_guard (p : α → Prop) [DecidablePred p] (a : α) :
+    Option.any q (guard p a) = (p a && q a) := by
+  simp only [guard]
+  split <;> simp_all
+
 theorem bind_map_comm {α β} {x : Option (Option α)} {f : α → β} :
     x.bind (Option.map f) = (x.map (Option.map f)).bind id := by cases x <;> simp
 
@@ -240,7 +261,7 @@ theorem liftOrGet_eq_or_eq {f : α → α → α} (h : ∀ a b, f a b = a ∨ f
 @[simp] theorem getD_map (f : α → β) (x : α) (o : Option α) :
   (o.map f).getD (f x) = f (getD o x) := by cases o <;> rfl
 
-section
+section choice
 
 attribute [local instance] Classical.propDecidable
 
@@ -256,7 +277,7 @@ theorem choice_eq {α : Type _} [Subsingleton α] (a : α) : choice α = some a
 theorem choice_isSome_iff_nonempty {α : Type _} : (choice α).isSome ↔ Nonempty α :=
   ⟨fun h => ⟨(choice α).get h⟩, fun h => by simp only [choice, dif_pos h, isSome_some]⟩
 
-end
+end choice
 
 @[simp] theorem toList_some (a : α) : (a : Option α).toList = [a] := rfl
 
@@ -304,3 +325,51 @@ theorem map_or : f <$> or o o' = (f <$> o).or (f <$> o') := by
 
 theorem map_or' : (or o o').map f = (o.map f).or (o'.map f) := by
   cases o <;> rfl
+
+theorem or_of_isSome {o o' : Option α} (h : o.isSome) : o.or o' = o := by
+  match o, h with
+  | some _, _ => simp
+
+theorem or_of_isNone {o o' : Option α} (h : o.isNone) : o.or o' = o' := by
+  match o, h with
+  | none, _ => simp
+
+section ite
+
+@[simp] theorem isSome_dite {p : Prop} [Decidable p] {b : p → β} :
+    (if h : p then some (b h) else none).isSome = true ↔ p := by
+  split <;> simpa
+@[simp] theorem isSome_ite {p : Prop} [Decidable p] :
+    (if p then some b else none).isSome = true ↔ p := by
+  split <;> simpa
+@[simp] theorem isSome_dite' {p : Prop} [Decidable p] {b : ¬ p → β} :
+    (if h : p then none else some (b h)).isSome = true ↔ ¬ p := by
+  split <;> simpa
+@[simp] theorem isSome_ite' {p : Prop} [Decidable p] :
+    (if p then none else some b).isSome = true ↔ ¬ p := by
+  split <;> simpa
+
+@[simp] theorem get_dite {p : Prop} [Decidable p] (b : p → β) (w) :
+    (if h : p then some (b h) else none).get w = b (by simpa using w) := by
+  split
+  · simp
+  · exfalso
+    simp at w
+    contradiction
+@[simp] theorem get_ite {p : Prop} [Decidable p] (h) :
+    (if p then some b else none).get h = b := by
+  simpa using get_dite (p := p) (fun _ => b) (by simpa using h)
+@[simp] theorem get_dite' {p : Prop} [Decidable p] (b : ¬ p → β) (w) :
+    (if h : p then none else some (b h)).get w = b (by simpa using w) := by
+  split
+  · exfalso
+    simp at w
+    contradiction
+  · simp
+@[simp] theorem get_ite' {p : Prop} [Decidable p] (h) :
+    (if p then none else some b).get h = b := by
+  simpa using get_dite' (p := p) (fun _ => b) (by simpa using h)
+
+end ite
+
+end Option

src/Init/Data/Prod.lean

@@ -5,9 +5,18 @@ Author: Leonardo de Moura
 -/
 prelude
 import Init.SimpLemmas
+import Init.NotationExtra
 
 instance [BEq α] [BEq β] [LawfulBEq α] [LawfulBEq β] : LawfulBEq (α × β) where
   eq_of_beq {a b} (h : a.1 == b.1 && a.2 == b.2) := by
     cases a; cases b
     refine congr (congrArg _ (eq_of_beq ?_)) (eq_of_beq ?_) <;> simp_all
   rfl {a} := by cases a; simp [BEq.beq, LawfulBEq.rfl]
+
+@[simp]
+protected theorem Prod.forall {p : α × β → Prop} : (∀ x, p x) ↔ ∀ a b, p (a, b) :=
+  ⟨fun h a b ↦ h (a, b), fun h ⟨a, b⟩ ↦ h a b⟩
+
+@[simp]
+protected theorem Prod.exists {p : α × β → Prop} : (∃ x, p x) ↔ ∃ a b, p (a, b) :=
+  ⟨fun ⟨⟨a, b⟩, h⟩ ↦ ⟨a, b, h⟩, fun ⟨a, b, h⟩ ↦ ⟨⟨a, b⟩, h⟩⟩

src/Init/Data/Queue.lean

@@ -7,7 +7,7 @@ Simple queue implemented using two lists.
 Note: this is only a temporary placeholder.
 -/
 prelude
-import Init.Data.List
+import Init.Data.Array.Basic
 
 namespace Std
 

src/Init/Data/Subtype.lean

@@ -0,0 +1,27 @@
+/-
+Copyright (c) 2017 Johannes Hölzl. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Johannes Hölzl
+-/
+prelude
+import Init.Ext
+
+namespace Subtype
+
+universe u
+variable {α : Sort u} {p q : α → Prop}
+
+@[ext]
+protected theorem ext : ∀ {a1 a2 : { x // p x }}, (a1 : α) = (a2 : α) → a1 = a2
+  | ⟨_, _⟩, ⟨_, _⟩, rfl => rfl
+
+@[simp]
+protected theorem «forall» {q : { a // p a } → Prop} : (∀ x, q x) ↔ ∀ a b, q ⟨a, b⟩ :=
+  ⟨fun h a b ↦ h ⟨a, b⟩, fun h ⟨a, b⟩ ↦ h a b⟩
+
+@[simp]
+protected theorem «exists» {q : { a // p a } → Prop} :
+    (Exists fun x => q x) ↔ Exists fun a => Exists fun b => q ⟨a, b⟩ :=
+  ⟨fun ⟨⟨a, b⟩, h⟩ ↦ ⟨a, b, h⟩, fun ⟨a, b, h⟩ ↦ ⟨⟨a, b⟩, h⟩⟩
+
+end Subtype

src/Init/Data/UInt/Lemmas.lean

@@ -47,11 +47,11 @@ protected theorem ne_of_val_ne {a b : $typeName} (h : a.val ≠ b.val) : a ≠ b
 open $typeName (ne_of_val_ne) in
 protected theorem ne_of_lt {a b : $typeName} (h : a < b) : a ≠ b := ne_of_val_ne (Fin.ne_of_lt h)
 
-@[simp] protected theorem zero_toNat : (0 : $typeName).toNat = 0 := Nat.zero_mod _
-@[simp] protected theorem mod_toNat (a b : $typeName) : (a % b).toNat = a.toNat % b.toNat := Fin.mod_val ..
-@[simp] protected theorem div_toNat (a b : $typeName) : (a / b).toNat = a.toNat / b.toNat := Fin.div_val ..
-@[simp] protected theorem sub_toNat_of_le (a b : $typeName) : b ≤ a → (a - b).toNat = a.toNat - b.toNat := Fin.sub_val_of_le
-@[simp] protected theorem modn_toNat (a : $typeName) (b : Nat) : (a.modn b).toNat = a.toNat % b := Fin.modn_val ..
+@[simp] protected theorem toNat_zero : (0 : $typeName).toNat = 0 := Nat.zero_mod _
+@[simp] protected theorem toNat_mod (a b : $typeName) : (a % b).toNat = a.toNat % b.toNat := Fin.mod_val ..
+@[simp] protected theorem toNat_div (a b : $typeName) : (a / b).toNat = a.toNat / b.toNat := Fin.div_val ..
+@[simp] protected theorem toNat_sub_of_le (a b : $typeName) : b ≤ a → (a - b).toNat = a.toNat - b.toNat := Fin.sub_val_of_le
+@[simp] protected theorem toNat_modn (a : $typeName) (b : Nat) : (a.modn b).toNat = a.toNat % b := Fin.modn_val ..
 protected theorem modn_lt {m : Nat} : ∀ (u : $typeName), m > 0 → toNat (u % m) < m
   | ⟨u⟩, h => Fin.modn_lt u h
 open $typeName (modn_lt) in
@@ -69,3 +69,28 @@ declare_uint_theorems UInt16
 declare_uint_theorems UInt32
 declare_uint_theorems UInt64
 declare_uint_theorems USize
+
+@[deprecated (since := "2024-06-23")] protected abbrev UInt8.zero_toNat := @UInt8.toNat_zero
+@[deprecated (since := "2024-06-23")] protected abbrev UInt8.div_toNat := @UInt8.toNat_div
+@[deprecated (since := "2024-06-23")] protected abbrev UInt8.mod_toNat := @UInt8.toNat_mod
+@[deprecated (since := "2024-06-23")] protected abbrev UInt8.modn_toNat := @UInt8.toNat_modn
+
+@[deprecated (since := "2024-06-23")] protected abbrev UInt16.zero_toNat := @UInt16.toNat_zero
+@[deprecated (since := "2024-06-23")] protected abbrev UInt16.div_toNat := @UInt16.toNat_div
+@[deprecated (since := "2024-06-23")] protected abbrev UInt16.mod_toNat := @UInt16.toNat_mod
+@[deprecated (since := "2024-06-23")] protected abbrev UInt16.modn_toNat := @UInt16.toNat_modn
+
+@[deprecated (since := "2024-06-23")] protected abbrev UInt32.zero_toNat := @UInt32.toNat_zero
+@[deprecated (since := "2024-06-23")] protected abbrev UInt32.div_toNat := @UInt32.toNat_div
+@[deprecated (since := "2024-06-23")] protected abbrev UInt32.mod_toNat := @UInt32.toNat_mod
+@[deprecated (since := "2024-06-23")] protected abbrev UInt32.modn_toNat := @UInt32.toNat_modn
+
+@[deprecated (since := "2024-06-23")] protected abbrev UInt64.zero_toNat := @UInt64.toNat_zero
+@[deprecated (since := "2024-06-23")] protected abbrev UInt64.div_toNat := @UInt64.toNat_div
+@[deprecated (since := "2024-06-23")] protected abbrev UInt64.mod_toNat := @UInt64.toNat_mod
+@[deprecated (since := "2024-06-23")] protected abbrev UInt64.modn_toNat := @UInt64.toNat_modn
+
+@[deprecated (since := "2024-06-23")] protected abbrev USize.zero_toNat := @USize.toNat_zero
+@[deprecated (since := "2024-06-23")] protected abbrev USize.div_toNat := @USize.toNat_div
+@[deprecated (since := "2024-06-23")] protected abbrev USize.mod_toNat := @USize.toNat_mod
+@[deprecated (since := "2024-06-23")] protected abbrev USize.modn_toNat := @USize.toNat_modn

src/Init/Ext.lean

@@ -78,7 +78,10 @@ end Elab.Tactic.Ext
 end Lean
 
 attribute [ext] Prod PProd Sigma PSigma
-attribute [ext] funext propext Subtype.eq
+attribute [ext] funext propext Subtype.eq Array.ext
 
 @[ext] protected theorem PUnit.ext (x y : PUnit) : x = y := rfl
 protected theorem Unit.ext (x y : Unit) : x = y := rfl
+
+@[ext] protected theorem Thunk.ext : {a b : Thunk α} → a.get = b.get → a = b
+  | {..}, {..}, heq => congrArg _ <| funext fun _ => heq

src/Init/Meta.lean

@@ -399,9 +399,16 @@ def setTailInfo (stx : Syntax) (info : SourceInfo) : Syntax :=
   | some stx => stx
   | none     => stx
 
+/--
+Replaces the trailing whitespace in `stx`, if any, with an empty substring.
+
+The trailing substring's `startPos` and `str` are preserved in order to ensure that the result could
+have been produced by the parser, in case any syntax consumers rely on such an assumption.
+-/
 def unsetTrailing (stx : Syntax) : Syntax :=
   match stx.getTailInfo with
-  | SourceInfo.original lead pos _ endPos => stx.setTailInfo (SourceInfo.original lead pos "".toSubstring endPos)
+  | SourceInfo.original lead pos trail endPos =>
+    stx.setTailInfo (SourceInfo.original lead pos { trail with stopPos := trail.startPos } endPos)
   | _                                     => stx
 
 @[specialize] private partial def updateFirst {α} [Inhabited α] (a : Array α) (f : α → Option α) (i : Nat) : Option (Array α) :=

src/Init/MetaTypes.lean

@@ -104,6 +104,11 @@ structure Config where
   That is, given a local context containing entry `x : t := e`, the free variable `x` reduces to `e`.
   -/
   zetaDelta         : Bool := false
+  /--
+  When `index` (default : `true`) is `false`, `simp` will only use the root symbol
+  to find candidate `simp` theorems. It approximates Lean 3 `simp` behavior.
+  -/
+  index             : Bool := true
   deriving Inhabited, BEq
 
 end DSimp
@@ -219,13 +224,13 @@ structure Config where
   -/
   index             : Bool := true
   /--
-  When `true` (default: `false`), `simp` will **not** create a proof for a rewriting rule associated
+  When `true` (default: `true`), `simp` will **not** create a proof for a rewriting rule associated
   with an `rfl`-theorem.
   Rewriting rules are provided by users by annotating theorems with the attribute `@[simp]`.
   If the proof of the theorem is just `rfl` (reflexivity), and `implicitDefEqProofs := true`, `simp`
   will **not** create a proof term which is an application of the annotated theorem.
   -/
-  implicitDefEqProofs : Bool := false
+  implicitDefEqProofs : Bool := true
   deriving Inhabited, BEq
 
 -- Configuration object for `simp_all`

src/Init/Notation.lean

@@ -704,6 +704,17 @@ syntax (name := checkSimp) "#check_simp " term "~>" term : command
 -/
 syntax (name := checkSimpFailure) "#check_simp " term "!~>" : command
 
+/--
+Time the elaboration of a command, and print the result (in milliseconds).
+
+Example usage:
+```
+set_option maxRecDepth 100000 in
+#time example : (List.range 500).length = 500 := rfl
+```
+-/
+syntax (name := timeCmd) "#time " command : command
+
 /--
 `#discr_tree_key  t` prints the discrimination tree keys for a term `t` (or, if it is a single identifier, the type of that constant).
 It uses the default configuration for generating keys.

src/Init/Omega/Int.lean

@@ -83,6 +83,10 @@ theorem neg_congr {a b : Int} (h₁ : a = b) : -a = -b := by
 theorem lt_of_gt {x y : Int} (h : x > y) : y < x := gt_iff_lt.mp h
 theorem le_of_ge {x y : Int} (h : x ≥ y) : y ≤ x := ge_iff_le.mp h
 
+theorem ofNat_mul_nonneg {a b : Nat} : 0 ≤ (a : Int) * b := by
+  rw [← Int.ofNat_mul]
+  exact Int.ofNat_zero_le (a * b)
+
 theorem ofNat_sub_eq_zero {b a : Nat} (h : ¬ b ≤ a) : ((a - b : Nat) : Int) = 0 :=
   Int.ofNat_eq_zero.mpr (Nat.sub_eq_zero_of_le (Nat.le_of_lt (Nat.not_le.mp h)))
 

src/Init/Omega/IntList.lean

@@ -4,7 +4,7 @@ Released under Apache 2.0 license as described in the file LICENSE.
 Authors: Scott Morrison
 -/
 prelude
-import Init.Data.List.Lemmas
+import Init.Data.List.Zip
 import Init.Data.Int.DivModLemmas
 import Init.Data.Nat.Gcd
 

src/Init/Prelude.lean

@@ -320,7 +320,7 @@ Because this is in the `Eq` namespace, if you have a variable `h : a = b`,
 
 For more information: [Equality](https://lean-lang.org/theorem_proving_in_lean4/quantifiers_and_equality.html#equality)
 -/
-theorem Eq.symm {α : Sort u} {a b : α} (h : Eq a b) : Eq b a :=
+@[symm] theorem Eq.symm {α : Sort u} {a b : α} (h : Eq a b) : Eq b a :=
   h ▸ rfl
 
 /--
@@ -1845,14 +1845,11 @@ theorem Fin.eq_of_val_eq {n} : ∀ {i j : Fin n}, Eq i.val j.val → Eq i j
 theorem Fin.val_eq_of_eq {n} {i j : Fin n} (h : Eq i j) : Eq i.val j.val :=
   h ▸ rfl
 
-theorem Fin.ne_of_val_ne {n} {i j : Fin n} (h : Not (Eq i.val j.val)) : Not (Eq i j) :=
-  fun h' => absurd (val_eq_of_eq h') h
-
 instance (n : Nat) : DecidableEq (Fin n) :=
   fun i j =>
     match decEq i.val j.val with
     | isTrue h  => isTrue (Fin.eq_of_val_eq h)
-    | isFalse h => isFalse (Fin.ne_of_val_ne h)
+    | isFalse h => isFalse (fun h' => absurd (Fin.val_eq_of_eq h') h)
 
 instance {n} : LT (Fin n) where
   lt a b := LT.lt a.val b.val
@@ -2214,12 +2211,17 @@ def Char.utf8Size (c : Char) : Nat :=
 or `none`. In functional programming languages, this type is used to represent
 the possibility of failure, or sometimes nullability.
 
-For example, the function `HashMap.find? : HashMap α β → α → Option β` looks up
+For example, the function `HashMap.get? : HashMap α β → α → Option β` looks up
 a specified key `a : α` inside the map. Because we do not know in advance
 whether the key is actually in the map, the return type is `Option β`, where
 `none` means the value was not in the map, and `some b` means that the value
 was found and `b` is the value retrieved.
 
+The `xs[i]` syntax, which is used to index into collections, has a variant
+`xs[i]?` that returns an optional value depending on whether the given index
+is valid. For example, if `m : HashMap α β` and `a : α`, then `m[a]?` is
+equivalent to `HashMap.get? m a`.
+
 To extract a value from an `Option α`, we use pattern matching:
 ```
 def map (f : α → β) (x : Option α) : Option β :=