chore: update stage0

Minor emendations to the List/Array API, collected from other PRs that
are still in the pipeline.

.github/ISSUE_TEMPLATE/bug_report.md

@@ -39,7 +39,7 @@ Please put an X between the brackets as you perform the following steps:
 
 ### Versions
 
-[Output of `#eval Lean.versionString`]
+[Output of `#version` or `#eval Lean.versionString`]
 [OS version, if not using live.lean-lang.org.]
 
 ### Additional Information

.github/PULL_REQUEST_TEMPLATE.md

@@ -5,6 +5,10 @@
 * Include the link to your `RFC` or `bug` issue in the description.
 * If the issue does not already have approval from a developer, submit the PR as draft.
 * The PR title/description will become the commit message. Keep it up-to-date as the PR evolves.
+* For `feat/fix` PRs, the first paragraph starting with "This PR" must be present and will become a
+  changelog entry unless the PR is labeled with `no-changelog`. If the PR does not have this label,
+  it must instead be categorized with one of the `changelog-*` labels (which will be done by a
+  reviewer for external PRs).
 * A toolchain of the form `leanprover/lean4-pr-releases:pr-release-NNNN` for Linux and M-series Macs will be generated upon build. To generate binaries for Windows and Intel-based Macs as well, write a comment containing `release-ci` on its own line.
 * If you rebase your PR onto `nightly-with-mathlib` then CI will test Mathlib against your PR.
 * You can manage the `awaiting-review`, `awaiting-author`, and `WIP` labels yourself, by writing a comment containing one of these labels on its own line.
@@ -12,4 +16,6 @@
 
 ---
 
-Closes #0000 (`RFC` or `bug` issue number fixed by this PR, if any)
+This PR <short changelog summary for feat/fix, see above>.
+
+Closes <`RFC` or `bug` issue number fixed by this PR, if any>

.github/dependabot.yml

@@ -0,0 +1,8 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "monthly"
+    commit-message:
+      prefix: "chore: CI"

.github/workflows/actionlint.yml

@@ -17,6 +17,6 @@ jobs:
     - name: Checkout
       uses: actions/checkout@v4
     - name: actionlint
-      uses: raven-actions/actionlint@v1
+      uses: raven-actions/actionlint@v2
       with:
         pyflakes: false # we do not use python scripts

.github/workflows/check-prelude.yml

@@ -11,7 +11,9 @@ jobs:
         with:
           # the default is to use a virtual merge commit between the PR and master: just use the PR
           ref: ${{ github.event.pull_request.head.sha }}
-          sparse-checkout: src/Lean
+          sparse-checkout: |
+            src/Lean
+            src/Std
       - name: Check Prelude
         run: |
           failed_files=""
@@ -19,8 +21,8 @@ jobs:
             if ! grep -q "^prelude$" "$file"; then
               failed_files="$failed_files$file\n"
             fi
-          done < <(find src/Lean -name '*.lean' -print0)
+          done < <(find src/Lean src/Std -name '*.lean' -print0)
           if [ -n "$failed_files" ]; then
             echo -e "The following files should use 'prelude':\n$failed_files"
             exit 1
-          fi
+          fi

.github/workflows/ci.yml

@@ -217,7 +217,7 @@ jobs:
                 "release": true,
                 "check-level": 2,
                 "shell": "msys2 {0}",
-                "CMAKE_OPTIONS": "-G \"Unix Makefiles\" -DUSE_GMP=OFF",
+                "CMAKE_OPTIONS": "-G \"Unix Makefiles\"",
                 // for reasons unknown, interactivetests are flaky on Windows
                 "CTEST_OPTIONS": "--repeat until-pass:2",
                 "llvm-url": "https://github.com/leanprover/lean-llvm/releases/download/15.0.1/lean-llvm-x86_64-w64-windows-gnu.tar.zst",
@@ -227,7 +227,7 @@ jobs:
               {
                 "name": "Linux aarch64",
                 "os": "nscloud-ubuntu-22.04-arm64-4x8",
-                "CMAKE_OPTIONS": "-DUSE_GMP=OFF -DLEAN_INSTALL_SUFFIX=-linux_aarch64",
+                "CMAKE_OPTIONS": "-DLEAN_INSTALL_SUFFIX=-linux_aarch64",
                 "release": true,
                 "check-level": 2,
                 "shell": "nix develop .#oldGlibcAArch -c bash -euxo pipefail {0}",
@@ -257,7 +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|leanruntest_libuv\\.lean\""
+                "CTEST_OPTIONS": "-R \"leantest_1007\\.lean|leantest_Format\\.lean|leanruntest\\_1037.lean|leanruntest_ac_rfl\\.lean|leanruntest_tempfile.lean\\.|leanruntest_libuv\\.lean\""
               }
             ];
             console.log(`matrix:\n${JSON.stringify(matrix, null, 2)}`)
@@ -318,7 +318,7 @@ jobs:
         if: github.event_name == 'pull_request'
       # (needs to be after "Checkout" so files don't get overridden)
       - name: Setup emsdk
-        uses: mymindstorm/setup-emsdk@v12
+        uses: mymindstorm/setup-emsdk@v14
         with:
           version: 3.1.44
           actions-cache-folder: emsdk
@@ -452,7 +452,7 @@ jobs:
         run: ccache -s
 
   # This job collects results from all the matrix jobs
-  # This can be made the “required” job, instead of listing each
+  # This can be made the "required" job, instead of listing each
   # matrix job separately
   all-done:
     name: Build matrix complete
@@ -492,7 +492,7 @@ jobs:
         with:
           path: artifacts
       - name: Release
-        uses: softprops/action-gh-release@v1
+        uses: softprops/action-gh-release@v2
         with:
           files: artifacts/*/*
           fail_on_unmatched_files: true
@@ -536,7 +536,7 @@ jobs:
           echo -e "\n*Full commit log*\n" >> diff.md
           git log --oneline "$last_tag"..HEAD | sed 's/^/* /' >> diff.md
       - name: Release Nightly
-        uses: softprops/action-gh-release@v1
+        uses: softprops/action-gh-release@v2
         with:
           body_path: diff.md
           prerelease: true

.github/workflows/nix-ci.yml

@@ -96,7 +96,7 @@ jobs:
           nix build $NIX_BUILD_ARGS .#cacheRoots -o push-build
       - name: Test
         run: |
-          nix build --keep-failed $NIX_BUILD_ARGS .#test -o push-test || (ln -s /tmp/nix-build-*/source/src/build/ ./push-test; false)
+          nix build --keep-failed $NIX_BUILD_ARGS .#test -o push-test || (ln -s /tmp/nix-build-*/build/source/src/build ./push-test; false)
       - name: Test Summary
         uses: test-summary/action@v2
         with:
@@ -110,14 +110,6 @@ jobs:
           # https://github.com/netlify/cli/issues/1809
           cp -r --dereference ./result ./dist
         if: matrix.name == 'Nix Linux'
-      - name: Check manual for broken links
-        id: lychee
-        uses: lycheeverse/lychee-action@v1.9.0
-        with:
-          fail: false  # report errors but do not block CI on temporary failures
-          # gmplib.org consistently times out from GH actions
-          # the GitHub token is to avoid rate limiting
-          args: --base './dist' --no-progress --github-token ${{ secrets.GITHUB_TOKEN }} --exclude 'gmplib.org' './dist/**/*.html'
       - name: Rebuild Nix Store Cache
         run: |
           rm -rf nix-store-cache || true
@@ -129,7 +121,7 @@ jobs:
           python3 -c 'import base64; print("alias="+base64.urlsafe_b64encode(bytes.fromhex("${{github.sha}}")).decode("utf-8").rstrip("="))' >> "$GITHUB_OUTPUT"
           echo "message=`git log -1 --pretty=format:"%s"`" >> "$GITHUB_OUTPUT"
       - name: Publish manual to Netlify
-        uses: nwtgck/actions-netlify@v2.0
+        uses: nwtgck/actions-netlify@v3.0
         id: publish-manual
         with:
           publish-dir: ./dist

.github/workflows/pr-body.yml

@@ -0,0 +1,23 @@
+name: Check PR body for changelog convention
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened, edited, labeled, converted_to_draft, ready_for_review]
+
+jobs:
+  check-pr-body:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check PR body
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const { title, body, labels, draft } = context.payload.pull_request;
+            if (!draft && /^(feat|fix):/.test(title) && !labels.some(label => label.name == "changelog-no")) {
+              if (!labels.some(label => label.name.startsWith("changelog-"))) {
+                core.setFailed('feat/fix PR must have a `changelog-*` label');
+              }
+              if (!/^This PR [^<]/.test(body)) {
+                core.setFailed('feat/fix PR must have changelog summary starting with "This PR ..." as first line.');
+              }
+            }

.github/workflows/pr-release.yml

@@ -34,7 +34,7 @@ jobs:
       - name: Download artifact from the previous workflow.
         if: ${{ steps.workflow-info.outputs.pullRequestNumber != '' }}
         id: download-artifact
-        uses: dawidd6/action-download-artifact@v2 # https://github.com/marketplace/actions/download-workflow-artifact
+        uses: dawidd6/action-download-artifact@v6 # https://github.com/marketplace/actions/download-workflow-artifact
         with:
           run_id: ${{ github.event.workflow_run.id }}
           path: artifacts
@@ -60,7 +60,7 @@ jobs:
           GH_TOKEN: ${{ secrets.PR_RELEASES_TOKEN }}
       - name: Release
         if: ${{ steps.workflow-info.outputs.pullRequestNumber != '' }}
-        uses: softprops/action-gh-release@v1
+        uses: softprops/action-gh-release@v2
         with:
           name: Release for PR ${{ steps.workflow-info.outputs.pullRequestNumber }}
           # There are coredumps files here as well, but all in deeper subdirectories.
@@ -75,7 +75,7 @@ jobs:
 
       - name: Report release status
         if: ${{ steps.workflow-info.outputs.pullRequestNumber != '' }}
-        uses: actions/github-script@v6
+        uses: actions/github-script@v7
         with:
           script: |
             await github.rest.repos.createCommitStatus({
@@ -111,7 +111,7 @@ jobs:
 
       - name: 'Setup jq'
         if: ${{ steps.workflow-info.outputs.pullRequestNumber != '' }}
-        uses: dcarbone/install-jq-action@v1.0.1
+        uses: dcarbone/install-jq-action@v2.1.0
 
       # Check that the most recently nightly coincides with 'git merge-base HEAD master'
       - name: Check merge-base and nightly-testing-YYYY-MM-DD
@@ -164,10 +164,10 @@ jobs:
 
             # Use GitHub API to check if a comment already exists
             existing_comment="$(curl --retry 3 --location --silent \
-                                    -H "Authorization: token ${{ secrets.MATHLIB4_BOT }}" \
+                                    -H "Authorization: token ${{ secrets.MATHLIB4_COMMENT_BOT }}" \
                                     -H "Accept: application/vnd.github.v3+json" \
                                     "https://api.github.com/repos/leanprover/lean4/issues/${{ steps.workflow-info.outputs.pullRequestNumber }}/comments" \
-                                    | jq 'first(.[] | select(.body | test("^- . Mathlib") or startswith("Mathlib CI status")) | select(.user.login == "leanprover-community-mathlib4-bot"))')"
+                                    | jq 'first(.[] | select(.body | test("^- . Mathlib") or startswith("Mathlib CI status")) | select(.user.login == "leanprover-community-bot"))')"
             existing_comment_id="$(echo "$existing_comment" | jq -r .id)"
             existing_comment_body="$(echo "$existing_comment" | jq -r .body)"
 
@@ -177,14 +177,14 @@ jobs:
               echo "Posting message to the comments: $MESSAGE"
 
               # Append new result to the existing comment or post a new comment
-              # It's essential we use the MATHLIB4_BOT token here, so that Mathlib CI can subsequently edit the comment.
+              # It's essential we use the MATHLIB4_COMMENT_BOT token here, so that Mathlib CI can subsequently edit the comment.
               if [ -z "$existing_comment_id" ]; then
                 INTRO="Mathlib CI status ([docs](https://leanprover-community.github.io/contribute/tags_and_branches.html)):"
                 # Post new comment with a bullet point
                 echo "Posting as new comment at leanprover/lean4/issues/${{ steps.workflow-info.outputs.pullRequestNumber }}/comments"
                 curl -L -s \
                   -X POST \
-                  -H "Authorization: token ${{ secrets.MATHLIB4_BOT }}" \
+                  -H "Authorization: token ${{ secrets.MATHLIB4_COMMENT_BOT }}" \
                   -H "Accept: application/vnd.github.v3+json" \
                   -d "$(jq --null-input --arg intro "$INTRO" --arg val "$MESSAGE" '{"body":($intro + "\n" + $val)}')" \
                   "https://api.github.com/repos/leanprover/lean4/issues/${{ steps.workflow-info.outputs.pullRequestNumber }}/comments"
@@ -193,7 +193,7 @@ jobs:
                 echo "Appending to existing comment at leanprover/lean4/issues/${{ steps.workflow-info.outputs.pullRequestNumber }}/comments"
                 curl -L -s \
                   -X PATCH \
-                  -H "Authorization: token ${{ secrets.MATHLIB4_BOT }}" \
+                  -H "Authorization: token ${{ secrets.MATHLIB4_COMMENT_BOT }}" \
                   -H "Accept: application/vnd.github.v3+json" \
                   -d "$(jq --null-input --arg existing "$existing_comment_body" --arg message "$MESSAGE" '{"body":($existing + "\n" + $message)}')" \
                   "https://api.github.com/repos/leanprover/lean4/issues/comments/$existing_comment_id"
@@ -208,7 +208,7 @@ jobs:
 
       - name: Report mathlib base
         if: ${{ steps.workflow-info.outputs.pullRequestNumber != '' && steps.ready.outputs.mathlib_ready == 'true' }}
-        uses: actions/github-script@v6
+        uses: actions/github-script@v7
         with:
           script: |
             const description =
@@ -340,6 +340,7 @@ jobs:
             # (This should no longer be possible once `nightly-testing-YYYY-MM-DD` is a tag, but it is still safe to merge.)
             git merge "$BASE" --strategy-option ours --no-commit --allow-unrelated-histories
             lake update batteries
+            git add lake-manifest.json
             git commit --allow-empty -m "Trigger CI for https://github.com/leanprover/lean4/pull/${{ steps.workflow-info.outputs.pullRequestNumber }}"
           fi
 

.github/workflows/stale.yml

@@ -11,7 +11,7 @@ jobs:
   stale:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/stale@v8
+      - uses: actions/stale@v9
         with:
           days-before-stale: -1
           days-before-pr-stale: 30

CODEOWNERS

@@ -4,14 +4,14 @@
 # Listed persons will automatically be asked by GitHub to review a PR touching these paths.
 # If multiple names are listed, a review by any of them is considered sufficient by default.
 
-/.github/ @Kha @semorrison
-/RELEASES.md @semorrison
+/.github/ @Kha @kim-em
+/RELEASES.md @kim-em
 /src/kernel/ @leodemoura
 /src/lake/ @tydeu
 /src/Lean/Compiler/ @leodemoura
 /src/Lean/Data/Lsp/ @mhuisi
-/src/Lean/Elab/Deriving/ @semorrison
-/src/Lean/Elab/Tactic/ @semorrison
+/src/Lean/Elab/Deriving/ @kim-em
+/src/Lean/Elab/Tactic/ @kim-em
 /src/Lean/Language/ @Kha
 /src/Lean/Meta/Tactic/ @leodemoura
 /src/Lean/Parser/ @Kha
@@ -19,7 +19,7 @@
 /src/Lean/PrettyPrinter/Delaborator/ @kmill
 /src/Lean/Server/ @mhuisi
 /src/Lean/Widget/ @Vtec234
-/src/Init/Data/ @semorrison
+/src/Init/Data/ @kim-em
 /src/Init/Data/Array/Lemmas.lean @digama0
 /src/Init/Data/List/Lemmas.lean @digama0
 /src/Init/Data/List/BasicAux.lean @digama0
@@ -45,3 +45,4 @@
 /src/Std/ @TwoFX
 /src/Std/Tactic/BVDecide/ @hargoniX
 /src/Lean/Elab/Tactic/BVDecide/ @hargoniX
+/src/Std/Sat/ @hargoniX

RELEASES.md

@@ -8,9 +8,642 @@ 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.
 
+v4.15.0
+----------
+
+Development in progress.
+
+v4.14.0
+----------
+
+Release candidate, release notes will be copied from the branch `releases/v4.14.0` once completed.
+
+v4.13.0
+----------
+
+**Full Changelog**: https://github.com/leanprover/lean4/compare/v4.12.0...v4.13.0
+
+### Language features, tactics, and metaprograms
+
+* `structure` command
+  * [#5511](https://github.com/leanprover/lean4/pull/5511) allows structure parents to be type synonyms.
+  * [#5531](https://github.com/leanprover/lean4/pull/5531) allows default values for structure fields to be noncomputable.
+
+* `rfl` and `apply_rfl` tactics
+  * [#3714](https://github.com/leanprover/lean4/pull/3714), [#3718](https://github.com/leanprover/lean4/pull/3718) improve the `rfl` tactic and give better error messages.
+  * [#3772](https://github.com/leanprover/lean4/pull/3772) makes `rfl` no longer use kernel defeq for ground terms.
+  * [#5329](https://github.com/leanprover/lean4/pull/5329) tags `Iff.refl` with `@[refl]` (@Parcly-Taxel)
+  * [#5359](https://github.com/leanprover/lean4/pull/5359) ensures that the `rfl` tactic tries `Iff.rfl` (@Parcly-Taxel)
+
+* `unfold` tactic
+  * [#4834](https://github.com/leanprover/lean4/pull/4834) let `unfold` do zeta-delta reduction of local definitions, incorporating functionality of the Mathlib `unfold_let` tactic.
+
+* `omega` tactic
+  * [#5382](https://github.com/leanprover/lean4/pull/5382) fixes spurious error in [#5315](https://github.com/leanprover/lean4/issues/5315)
+  * [#5523](https://github.com/leanprover/lean4/pull/5523) supports `Int.toNat`
+
+* `simp` tactic
+  * [#5479](https://github.com/leanprover/lean4/pull/5479) lets `simp` apply rules with higher-order patterns.
+
+* `induction` tactic
+  * [#5494](https://github.com/leanprover/lean4/pull/5494) fixes `induction`’s "pre-tactic" block to always be indented, avoiding unintended uses of it.
+
+* `ac_nf` tactic
+  * [#5524](https://github.com/leanprover/lean4/pull/5524) adds `ac_nf`, a counterpart to `ac_rfl`, for normalizing expressions with respect to associativity and commutativity. Tests it with `BitVec` expressions.
+
+* `bv_decide`
+  * [#5211](https://github.com/leanprover/lean4/pull/5211) makes `extractLsb'` the primitive `bv_decide` understands, rather than `extractLsb` (@alexkeizer)
+  * [#5365](https://github.com/leanprover/lean4/pull/5365) adds `bv_decide` diagnoses.
+  * [#5375](https://github.com/leanprover/lean4/pull/5375) adds `bv_decide` normalization rules for `ofBool (a.getLsbD i)` and `ofBool a[i]` (@alexkeizer)
+  * [#5423](https://github.com/leanprover/lean4/pull/5423) enhances the rewriting rules of `bv_decide`
+  * [#5433](https://github.com/leanprover/lean4/pull/5433) presents the `bv_decide` counterexample at the API
+  * [#5484](https://github.com/leanprover/lean4/pull/5484) handles `BitVec.ofNat` with `Nat` fvars in `bv_decide`
+  * [#5506](https://github.com/leanprover/lean4/pull/5506), [#5507](https://github.com/leanprover/lean4/pull/5507) add `bv_normalize` rules.
+  * [#5568](https://github.com/leanprover/lean4/pull/5568) generalize the `bv_normalize` pipeline to support more general preprocessing passes
+  * [#5573](https://github.com/leanprover/lean4/pull/5573) gets `bv_normalize` up-to-date with the current `BitVec` rewrites
+  * Cleanups: [#5408](https://github.com/leanprover/lean4/pull/5408), [#5493](https://github.com/leanprover/lean4/pull/5493), [#5578](https://github.com/leanprover/lean4/pull/5578)
+
+
+* Elaboration improvements
+  * [#5266](https://github.com/leanprover/lean4/pull/5266) preserve order of overapplied arguments in `elab_as_elim` procedure.
+  * [#5510](https://github.com/leanprover/lean4/pull/5510) generalizes `elab_as_elim` to allow arbitrary motive applications.
+  * [#5283](https://github.com/leanprover/lean4/pull/5283), [#5512](https://github.com/leanprover/lean4/pull/5512) refine how named arguments suppress explicit arguments. Breaking change: some previously omitted explicit arguments may need explicit `_` arguments now.
+  * [#5376](https://github.com/leanprover/lean4/pull/5376) modifies projection instance binder info for instances, making parameters that are instance implicit in the type be implicit.
+  * [#5402](https://github.com/leanprover/lean4/pull/5402) localizes universe metavariable errors to `let` bindings and `fun` binders if possible. Makes "cannot synthesize metavariable" errors take precedence over unsolved universe level errors.
+  * [#5419](https://github.com/leanprover/lean4/pull/5419) must not reduce `ite` in the discriminant of `match`-expression when reducibility setting is `.reducible`
+  * [#5474](https://github.com/leanprover/lean4/pull/5474) have autoparams report parameter/field on failure
+  * [#5530](https://github.com/leanprover/lean4/pull/5530) makes automatic instance names about types with hygienic names be hygienic.
+
+* Deriving handlers
+  * [#5432](https://github.com/leanprover/lean4/pull/5432) makes `Repr` deriving instance handle explicit type parameters
+
+* Functional induction
+  * [#5364](https://github.com/leanprover/lean4/pull/5364) adds more equalities in context, more careful cleanup.
+
+* Linters
+  * [#5335](https://github.com/leanprover/lean4/pull/5335) fixes the unused variables linter complaining about match/tactic combinations
+  * [#5337](https://github.com/leanprover/lean4/pull/5337) fixes the unused variables linter complaining about some wildcard patterns
+
+* Other fixes
+  * [#4768](https://github.com/leanprover/lean4/pull/4768) fixes a parse error when `..` appears with a `.` on the next line
+
+* Metaprogramming
+  * [#3090](https://github.com/leanprover/lean4/pull/3090) handles level parameters in `Meta.evalExpr` (@eric-wieser)  
+  * [#5401](https://github.com/leanprover/lean4/pull/5401) instance for `Inhabited (TacticM α)` (@alexkeizer)
+  * [#5412](https://github.com/leanprover/lean4/pull/5412) expose Kernel.check for debugging purposes
+  * [#5556](https://github.com/leanprover/lean4/pull/5556) improves the "invalid projection" type inference error in `inferType`.
+  * [#5587](https://github.com/leanprover/lean4/pull/5587) allows `MVarId.assertHypotheses` to set `BinderInfo` and `LocalDeclKind`.
+  * [#5588](https://github.com/leanprover/lean4/pull/5588) adds `MVarId.tryClearMany'`, a variant of `MVarId.tryClearMany`.
+
+
+
+### Language server, widgets, and IDE extensions
+
+* [#5205](https://github.com/leanprover/lean4/pull/5205) decreases the latency of auto-completion in tactic blocks.
+* [#5237](https://github.com/leanprover/lean4/pull/5237) fixes symbol occurrence highlighting in VS Code not highlighting occurrences when moving the text cursor into the identifier from the right.
+* [#5257](https://github.com/leanprover/lean4/pull/5257) fixes several instances of incorrect auto-completions being reported.
+* [#5299](https://github.com/leanprover/lean4/pull/5299) allows auto-completion to report completions for global identifiers when the elaborator fails to provide context-specific auto-completions.
+* [#5312](https://github.com/leanprover/lean4/pull/5312) fixes the server breaking when changing whitespace after the module header.
+* [#5322](https://github.com/leanprover/lean4/pull/5322) fixes several instances of auto-completion reporting non-existent namespaces.
+* [#5428](https://github.com/leanprover/lean4/pull/5428) makes sure to always report some recent file range as progress when waiting for elaboration.
+
+
+### Pretty printing
+
+* [#4979](https://github.com/leanprover/lean4/pull/4979) make pretty printer escape identifiers that are tokens.
+* [#5389](https://github.com/leanprover/lean4/pull/5389) makes formatter use the current token table.
+* [#5513](https://github.com/leanprover/lean4/pull/5513) use breakable instead of unbreakable whitespace when formatting tokens.
+
+
+### Library
+
+* [#5222](https://github.com/leanprover/lean4/pull/5222) reduces allocations in `Json.compress`.
+* [#5231](https://github.com/leanprover/lean4/pull/5231) upstreams `Zero` and `NeZero`
+* [#5292](https://github.com/leanprover/lean4/pull/5292) refactors `Lean.Elab.Deriving.FromToJson` (@arthur-adjedj)
+* [#5415](https://github.com/leanprover/lean4/pull/5415) implements `Repr Empty` (@TomasPuverle)
+* [#5421](https://github.com/leanprover/lean4/pull/5421) implements `To/FromJSON Empty` (@TomasPuverle)
+
+* Logic
+  * [#5263](https://github.com/leanprover/lean4/pull/5263) allows simplifying `dite_not`/`decide_not` with only `Decidable (¬p)`.
+  * [#5268](https://github.com/leanprover/lean4/pull/5268) fixes binders on `ite_eq_left_iff`
+  * [#5284](https://github.com/leanprover/lean4/pull/5284) turns off `Inhabited (Sum α β)` instances
+  * [#5355](https://github.com/leanprover/lean4/pull/5355) adds simp lemmas for `LawfulBEq`
+  * [#5374](https://github.com/leanprover/lean4/pull/5374) add `Nonempty` instances for products, allowing more `partial` functions to elaborate successfully
+  * [#5447](https://github.com/leanprover/lean4/pull/5447) updates Pi instance names
+  * [#5454](https://github.com/leanprover/lean4/pull/5454) makes some instance arguments implicit
+  * [#5456](https://github.com/leanprover/lean4/pull/5456) adds `heq_comm`
+  * [#5529](https://github.com/leanprover/lean4/pull/5529) moves `@[simp]` from `exists_prop'` to `exists_prop`
+
+* `Bool`
+  * [#5228](https://github.com/leanprover/lean4/pull/5228) fills gaps in Bool lemmas
+  * [#5332](https://github.com/leanprover/lean4/pull/5332) adds notation `^^` for Bool.xor
+  * [#5351](https://github.com/leanprover/lean4/pull/5351) removes `_root_.and` (and or/not/xor) and instead exports/uses `Bool.and` (etc.).
+
+* `BitVec`
+  * [#5240](https://github.com/leanprover/lean4/pull/5240) removes BitVec simps with complicated RHS
+  * [#5247](https://github.com/leanprover/lean4/pull/5247) `BitVec.getElem_zeroExtend`
+  * [#5248](https://github.com/leanprover/lean4/pull/5248) simp lemmas for BitVec, improving confluence
+  * [#5249](https://github.com/leanprover/lean4/pull/5249) removes `@[simp]` from some BitVec lemmas
+  * [#5252](https://github.com/leanprover/lean4/pull/5252) changes `BitVec.intMin/Max` from abbrev to def
+  * [#5278](https://github.com/leanprover/lean4/pull/5278) adds `BitVec.getElem_truncate` (@tobiasgrosser)
+  * [#5281](https://github.com/leanprover/lean4/pull/5281) adds udiv/umod bitblasting for `bv_decide` (@bollu)
+  * [#5297](https://github.com/leanprover/lean4/pull/5297) `BitVec` unsigned order theoretic results
+  * [#5313](https://github.com/leanprover/lean4/pull/5313) adds more basic BitVec ordering theory for UInt
+  * [#5314](https://github.com/leanprover/lean4/pull/5314) adds `toNat_sub_of_le` (@bollu)
+  * [#5357](https://github.com/leanprover/lean4/pull/5357) adds `BitVec.truncate` lemmas
+  * [#5358](https://github.com/leanprover/lean4/pull/5358) introduces `BitVec.setWidth` to unify zeroExtend and truncate (@tobiasgrosser)
+  * [#5361](https://github.com/leanprover/lean4/pull/5361) some BitVec GetElem lemmas
+  * [#5385](https://github.com/leanprover/lean4/pull/5385) adds `BitVec.ofBool_[and|or|xor]_ofBool` theorems (@tobiasgrosser)
+  * [#5404](https://github.com/leanprover/lean4/pull/5404) more of `BitVec.getElem_*` (@tobiasgrosser)
+  * [#5410](https://github.com/leanprover/lean4/pull/5410) BitVec analogues of `Nat.{mul_two, two_mul, mul_succ, succ_mul}` (@bollu)
+  * [#5411](https://github.com/leanprover/lean4/pull/5411) `BitVec.toNat_{add,sub,mul_of_lt}` for BitVector non-overflow reasoning (@bollu)
+  * [#5413](https://github.com/leanprover/lean4/pull/5413) adds `_self`, `_zero`, and `_allOnes` for `BitVec.[and|or|xor]` (@tobiasgrosser)
+  * [#5416](https://github.com/leanprover/lean4/pull/5416) adds LawCommIdentity + IdempotentOp for `BitVec.[and|or|xor]` (@tobiasgrosser)
+  * [#5418](https://github.com/leanprover/lean4/pull/5418) decidable quantifers for BitVec
+  * [#5450](https://github.com/leanprover/lean4/pull/5450) adds `BitVec.toInt_[intMin|neg|neg_of_ne_intMin]` (@tobiasgrosser)
+  * [#5459](https://github.com/leanprover/lean4/pull/5459) missing BitVec lemmas
+  * [#5469](https://github.com/leanprover/lean4/pull/5469) adds `BitVec.[not_not, allOnes_shiftLeft_or_shiftLeft, allOnes_shiftLeft_and_shiftLeft]` (@luisacicolini)
+  * [#5478](https://github.com/leanprover/lean4/pull/5478) adds `BitVec.(shiftLeft_add_distrib, shiftLeft_ushiftRight)` (@luisacicolini)
+  * [#5487](https://github.com/leanprover/lean4/pull/5487) adds `sdiv_eq`, `smod_eq` to allow `sdiv`/`smod` bitblasting (@bollu)
+  * [#5491](https://github.com/leanprover/lean4/pull/5491) adds `BitVec.toNat_[abs|sdiv|smod]` (@tobiasgrosser)
+  * [#5492](https://github.com/leanprover/lean4/pull/5492) `BitVec.(not_sshiftRight, not_sshiftRight_not, getMsb_not, msb_not)` (@luisacicolini)
+  * [#5499](https://github.com/leanprover/lean4/pull/5499) `BitVec.Lemmas` - drop non-terminal simps (@tobiasgrosser)
+  * [#5505](https://github.com/leanprover/lean4/pull/5505) unsimps `BitVec.divRec_succ'`
+  * [#5508](https://github.com/leanprover/lean4/pull/5508) adds `BitVec.getElem_[add|add_add_bool|mul|rotateLeft|rotateRight…` (@tobiasgrosser)
+  * [#5554](https://github.com/leanprover/lean4/pull/5554) adds `Bitvec.[add, sub, mul]_eq_xor` and `width_one_cases` (@luisacicolini)
+
+* `List`
+  * [#5242](https://github.com/leanprover/lean4/pull/5242) improve naming for `List.mergeSort` lemmas
+  * [#5302](https://github.com/leanprover/lean4/pull/5302) provide `mergeSort` comparator autoParam
+  * [#5373](https://github.com/leanprover/lean4/pull/5373) fix name of `List.length_mergeSort`
+  * [#5377](https://github.com/leanprover/lean4/pull/5377) upstream `map_mergeSort`
+  * [#5378](https://github.com/leanprover/lean4/pull/5378) modify signature of lemmas about `mergeSort`
+  * [#5245](https://github.com/leanprover/lean4/pull/5245) avoid importing `List.Basic` without List.Impl
+  * [#5260](https://github.com/leanprover/lean4/pull/5260) review of List API
+  * [#5264](https://github.com/leanprover/lean4/pull/5264) review of List API
+  * [#5269](https://github.com/leanprover/lean4/pull/5269) remove HashMap's duplicated Pairwise and Sublist
+  * [#5271](https://github.com/leanprover/lean4/pull/5271) remove @[simp] from `List.head_mem` and similar
+  * [#5273](https://github.com/leanprover/lean4/pull/5273) lemmas about `List.attach`
+  * [#5275](https://github.com/leanprover/lean4/pull/5275) reverse direction of `List.tail_map`
+  * [#5277](https://github.com/leanprover/lean4/pull/5277) more `List.attach` lemmas
+  * [#5285](https://github.com/leanprover/lean4/pull/5285) `List.count` lemmas
+  * [#5287](https://github.com/leanprover/lean4/pull/5287) use boolean predicates in `List.filter`
+  * [#5289](https://github.com/leanprover/lean4/pull/5289) `List.mem_ite_nil_left` and analogues
+  * [#5293](https://github.com/leanprover/lean4/pull/5293) cleanup of `List.findIdx` / `List.take` lemmas
+  * [#5294](https://github.com/leanprover/lean4/pull/5294) switch primes on `List.getElem_take`
+  * [#5300](https://github.com/leanprover/lean4/pull/5300) more `List.findIdx` theorems
+  * [#5310](https://github.com/leanprover/lean4/pull/5310) fix `List.all/any` lemmas
+  * [#5311](https://github.com/leanprover/lean4/pull/5311) fix `List.countP` lemmas
+  * [#5316](https://github.com/leanprover/lean4/pull/5316) `List.tail` lemma
+  * [#5331](https://github.com/leanprover/lean4/pull/5331) fix implicitness of `List.getElem_mem`
+  * [#5350](https://github.com/leanprover/lean4/pull/5350) `List.replicate` lemmas
+  * [#5352](https://github.com/leanprover/lean4/pull/5352) `List.attachWith` lemmas
+  * [#5353](https://github.com/leanprover/lean4/pull/5353) `List.head_mem_head?`
+  * [#5360](https://github.com/leanprover/lean4/pull/5360) lemmas about `List.tail`
+  * [#5391](https://github.com/leanprover/lean4/pull/5391) review of `List.erase` / `List.find` lemmas
+  * [#5392](https://github.com/leanprover/lean4/pull/5392) `List.fold` / `attach` lemmas
+  * [#5393](https://github.com/leanprover/lean4/pull/5393) `List.fold` relators
+  * [#5394](https://github.com/leanprover/lean4/pull/5394) lemmas about `List.maximum?`
+  * [#5403](https://github.com/leanprover/lean4/pull/5403) theorems about `List.toArray`
+  * [#5405](https://github.com/leanprover/lean4/pull/5405) reverse direction of `List.set_map`
+  * [#5448](https://github.com/leanprover/lean4/pull/5448) add lemmas about `List.IsPrefix` (@Command-Master)
+  * [#5460](https://github.com/leanprover/lean4/pull/5460) missing `List.set_replicate_self`
+  * [#5518](https://github.com/leanprover/lean4/pull/5518) rename `List.maximum?` to `max?`
+  * [#5519](https://github.com/leanprover/lean4/pull/5519) upstream `List.fold` lemmas
+  * [#5520](https://github.com/leanprover/lean4/pull/5520) restore `@[simp]` on `List.getElem_mem` etc.
+  * [#5521](https://github.com/leanprover/lean4/pull/5521) List simp fixes
+  * [#5550](https://github.com/leanprover/lean4/pull/5550) `List.unattach` and simp lemmas
+  * [#5594](https://github.com/leanprover/lean4/pull/5594) induction-friendly `List.min?_cons`
+
+* `Array`
+  * [#5246](https://github.com/leanprover/lean4/pull/5246) cleanup imports of Array.Lemmas
+  * [#5255](https://github.com/leanprover/lean4/pull/5255) split Init.Data.Array.Lemmas for better bootstrapping
+  * [#5288](https://github.com/leanprover/lean4/pull/5288) rename `Array.data` to `Array.toList`
+  * [#5303](https://github.com/leanprover/lean4/pull/5303) cleanup of `List.getElem_append` variants
+  * [#5304](https://github.com/leanprover/lean4/pull/5304) `Array.not_mem_empty`
+  * [#5400](https://github.com/leanprover/lean4/pull/5400) reorganization in Array/Basic
+  * [#5420](https://github.com/leanprover/lean4/pull/5420) make `Array` functions either semireducible or use structural recursion
+  * [#5422](https://github.com/leanprover/lean4/pull/5422) refactor `DecidableEq (Array α)`
+  * [#5452](https://github.com/leanprover/lean4/pull/5452) refactor of Array
+  * [#5458](https://github.com/leanprover/lean4/pull/5458) cleanup of Array docstrings after refactor
+  * [#5461](https://github.com/leanprover/lean4/pull/5461) restore `@[simp]` on `Array.swapAt!_def`
+  * [#5465](https://github.com/leanprover/lean4/pull/5465) improve Array GetElem lemmas
+  * [#5466](https://github.com/leanprover/lean4/pull/5466) `Array.foldX` lemmas
+  * [#5472](https://github.com/leanprover/lean4/pull/5472) @[simp] lemmas about `List.toArray`
+  * [#5485](https://github.com/leanprover/lean4/pull/5485) reverse simp direction for `toArray_concat`
+  * [#5514](https://github.com/leanprover/lean4/pull/5514) `Array.eraseReps`
+  * [#5515](https://github.com/leanprover/lean4/pull/5515) upstream `Array.qsortOrd`
+  * [#5516](https://github.com/leanprover/lean4/pull/5516) upstream `Subarray.empty`
+  * [#5526](https://github.com/leanprover/lean4/pull/5526) fix name of `Array.length_toList`
+  * [#5527](https://github.com/leanprover/lean4/pull/5527) reduce use of deprecated lemmas in Array
+  * [#5534](https://github.com/leanprover/lean4/pull/5534) cleanup of Array GetElem lemmas
+  * [#5536](https://github.com/leanprover/lean4/pull/5536) fix `Array.modify` lemmas
+  * [#5551](https://github.com/leanprover/lean4/pull/5551) upstream `Array.flatten` lemmas
+  * [#5552](https://github.com/leanprover/lean4/pull/5552) switch obvious cases of array "bang"`[]!` indexing to rely on hypothesis (@TomasPuverle)
+  * [#5577](https://github.com/leanprover/lean4/pull/5577) add missing simp to `Array.size_feraseIdx`
+  * [#5586](https://github.com/leanprover/lean4/pull/5586) `Array/Option.unattach`
+
+* `Option`
+  * [#5272](https://github.com/leanprover/lean4/pull/5272) remove @[simp] from `Option.pmap/pbind` and add simp lemmas
+  * [#5307](https://github.com/leanprover/lean4/pull/5307) restoring Option simp confluence
+  * [#5354](https://github.com/leanprover/lean4/pull/5354) remove @[simp] from `Option.bind_map`
+  * [#5532](https://github.com/leanprover/lean4/pull/5532) `Option.attach`
+  * [#5539](https://github.com/leanprover/lean4/pull/5539) fix explicitness of `Option.mem_toList`
+
+* `Nat`
+  * [#5241](https://github.com/leanprover/lean4/pull/5241) add @[simp] to `Nat.add_eq_zero_iff`
+  * [#5261](https://github.com/leanprover/lean4/pull/5261) Nat bitwise lemmas
+  * [#5262](https://github.com/leanprover/lean4/pull/5262) `Nat.testBit_add_one` should not be a global simp lemma
+  * [#5267](https://github.com/leanprover/lean4/pull/5267) protect some Nat bitwise theorems
+  * [#5305](https://github.com/leanprover/lean4/pull/5305) rename Nat bitwise lemmas
+  * [#5306](https://github.com/leanprover/lean4/pull/5306) add `Nat.self_sub_mod` lemma
+  * [#5503](https://github.com/leanprover/lean4/pull/5503) restore @[simp] to upstreamed `Nat.lt_off_iff`
+
+* `Int`
+  * [#5301](https://github.com/leanprover/lean4/pull/5301) rename `Int.div/mod` to `Int.tdiv/tmod`
+  * [#5320](https://github.com/leanprover/lean4/pull/5320) add `ediv_nonneg_of_nonpos_of_nonpos` to DivModLemmas (@sakehl)
+
+* `Fin`
+  * [#5250](https://github.com/leanprover/lean4/pull/5250) missing lemma about `Fin.ofNat'`
+  * [#5356](https://github.com/leanprover/lean4/pull/5356) `Fin.ofNat'` uses `NeZero`
+  * [#5379](https://github.com/leanprover/lean4/pull/5379) remove some @[simp]s from Fin lemmas
+  * [#5380](https://github.com/leanprover/lean4/pull/5380) missing Fin @[simp] lemmas
+
+* `HashMap`
+  * [#5244](https://github.com/leanprover/lean4/pull/5244) (`DHashMap`|`HashMap`|`HashSet`).(`getKey?`|`getKey`|`getKey!`|`getKeyD`)
+  * [#5362](https://github.com/leanprover/lean4/pull/5362) remove the last use of `Lean.(HashSet|HashMap)`
+  * [#5369](https://github.com/leanprover/lean4/pull/5369) `HashSet.ofArray`
+  * [#5370](https://github.com/leanprover/lean4/pull/5370) `HashSet.partition`
+  * [#5581](https://github.com/leanprover/lean4/pull/5581) `Singleton`/`Insert`/`Union` instances for `HashMap`/`Set`
+  * [#5582](https://github.com/leanprover/lean4/pull/5582) `HashSet.all`/`any`
+  * [#5590](https://github.com/leanprover/lean4/pull/5590) adding `Insert`/`Singleton`/`Union` instances for `HashMap`/`Set.Raw`
+  * [#5591](https://github.com/leanprover/lean4/pull/5591) `HashSet.Raw.all/any`
+
+* `Monads`
+  * [#5463](https://github.com/leanprover/lean4/pull/5463) upstream some monad lemmas
+  * [#5464](https://github.com/leanprover/lean4/pull/5464) adjust simp attributes on monad lemmas
+  * [#5522](https://github.com/leanprover/lean4/pull/5522) more monadic simp lemmas
+
+* Simp lemma cleanup
+  * [#5251](https://github.com/leanprover/lean4/pull/5251) remove redundant simp annotations
+  * [#5253](https://github.com/leanprover/lean4/pull/5253) remove Int simp lemmas that can't fire
+  * [#5254](https://github.com/leanprover/lean4/pull/5254) variables appearing on both sides of an iff should be implicit
+  * [#5381](https://github.com/leanprover/lean4/pull/5381) cleaning up redundant simp lemmas
+
+
+### Compiler, runtime, and FFI
+
+* [#4685](https://github.com/leanprover/lean4/pull/4685) fixes a typo in the C `run_new_frontend` signature
+* [#4729](https://github.com/leanprover/lean4/pull/4729) has IR checker suggest using `noncomputable`
+* [#5143](https://github.com/leanprover/lean4/pull/5143) adds a shared library for Lake
+* [#5437](https://github.com/leanprover/lean4/pull/5437) removes (syntactically) duplicate imports (@euprunin)
+* [#5462](https://github.com/leanprover/lean4/pull/5462) updates `src/lake/lakefile.toml` to the adjusted Lake build process
+* [#5541](https://github.com/leanprover/lean4/pull/5541) removes new shared libs before build to better support Windows
+* [#5558](https://github.com/leanprover/lean4/pull/5558) make `lean.h` compile with MSVC (@kant2002)
+* [#5564](https://github.com/leanprover/lean4/pull/5564) removes non-conforming size-0 arrays (@eric-wieser)
+
+
+### Lake
+  * Reservoir build cache. Lake will now attempt to fetch a pre-built copy of the package from Reservoir before building it. This is only enabled for packages in the leanprover or leanprover-community organizations on versions indexed by Reservoir. Users can force Lake to build packages from the source by passing --no-cache on the CLI or by setting the  LAKE_NO_CACHE environment variable to true. [#5486](https://github.com/leanprover/lean4/pull/5486), [#5572](https://github.com/leanprover/lean4/pull/5572), [#5583](https://github.com/leanprover/lean4/pull/5583), [#5600](https://github.com/leanprover/lean4/pull/5600), [#5641](https://github.com/leanprover/lean4/pull/5641), [#5642](https://github.com/leanprover/lean4/pull/5642).
+  * [#5504](https://github.com/leanprover/lean4/pull/5504) lake new and lake init now produce TOML configurations by default.
+  * [#5878](https://github.com/leanprover/lean4/pull/5878) fixes a serious issue where Lake would delete path dependencies when attempting to cleanup a dependency required with an incorrect name.
+
+  * **Breaking changes**
+    * [#5641](https://github.com/leanprover/lean4/pull/5641) A Lake build of target within a package will no longer build a package's dependencies package-level extra target dependencies. At the technical level, a package's extraDep facet no longer transitively builds its dependencies’ extraDep facets (which include their extraDepTargets).
+
+### Documentation fixes
+
+* [#3918](https://github.com/leanprover/lean4/pull/3918) `@[builtin_doc]` attribute (@digama0)
+* [#4305](https://github.com/leanprover/lean4/pull/4305) explains the borrow syntax (@eric-wieser)
+* [#5349](https://github.com/leanprover/lean4/pull/5349) adds documentation for `groupBy.loop` (@vihdzp)
+* [#5473](https://github.com/leanprover/lean4/pull/5473) fixes typo in `BitVec.mul` docstring (@llllvvuu)
+* [#5476](https://github.com/leanprover/lean4/pull/5476) fixes typos in `Lean.MetavarContext`
+* [#5481](https://github.com/leanprover/lean4/pull/5481) removes mention of `Lean.withSeconds` (@alexkeizer)
+* [#5497](https://github.com/leanprover/lean4/pull/5497) updates documentation and tests for `toUIntX` functions (@TomasPuverle)
+* [#5087](https://github.com/leanprover/lean4/pull/5087) mentions that `inferType` does not ensure type correctness
+* Many fixes to spelling across the doc-strings, (@euprunin): [#5425](https://github.com/leanprover/lean4/pull/5425) [#5426](https://github.com/leanprover/lean4/pull/5426) [#5427](https://github.com/leanprover/lean4/pull/5427) [#5430](https://github.com/leanprover/lean4/pull/5430)  [#5431](https://github.com/leanprover/lean4/pull/5431) [#5434](https://github.com/leanprover/lean4/pull/5434) [#5435](https://github.com/leanprover/lean4/pull/5435) [#5436](https://github.com/leanprover/lean4/pull/5436) [#5438](https://github.com/leanprover/lean4/pull/5438) [#5439](https://github.com/leanprover/lean4/pull/5439) [#5440](https://github.com/leanprover/lean4/pull/5440) [#5599](https://github.com/leanprover/lean4/pull/5599)
+
+### Changes to CI
+
+* [#5343](https://github.com/leanprover/lean4/pull/5343) allows addition of `release-ci` label via comment (@thorimur)
+* [#5344](https://github.com/leanprover/lean4/pull/5344) sets check level correctly during workflow (@thorimur)
+* [#5444](https://github.com/leanprover/lean4/pull/5444) Mathlib's `lean-pr-testing-NNNN` branches should use Batteries' `lean-pr-testing-NNNN` branches
+* [#5489](https://github.com/leanprover/lean4/pull/5489) commit `lake-manifest.json` when updating `lean-pr-testing` branches
+* [#5490](https://github.com/leanprover/lean4/pull/5490) use separate secrets for commenting and branching in `pr-release.yml`
+
 v4.12.0
 ----------
-Development in progress.
+
+### Language features, tactics, and metaprograms
+
+* `bv_decide` tactic. This release introduces a new tactic for proving goals involving `BitVec` and `Bool`. It reduces the goal to a SAT instance that is refuted by an external solver, and the resulting LRAT proof is checked in Lean. This is used to synthesize a proof of the goal by reflection. As this process uses verified algorithms, proofs generated by this tactic use `Lean.ofReduceBool`, so this tactic includes the Lean compiler as part of the trusted code base. The external solver CaDiCaL is included with Lean and does not need to be installed separately to make use of `bv_decide`.
+
+  For example, we can use `bv_decide` to verify that a bit twiddling formula leaves at most one bit set:
+  ```lean
+  def popcount (x : BitVec 64) : BitVec 64 :=
+    let rec go (x pop : BitVec 64) : Nat → BitVec 64
+      | 0 => pop
+      | n + 1 => go (x >>> 2) (pop + (x &&& 1)) n
+    go x 0 64
+
+  example (x : BitVec 64) : popcount ((x &&& (x - 1)) ^^^ x) ≤ 1 := by
+    simp only [popcount, popcount.go]
+    bv_decide
+  ```
+  When the external solver fails to refute the SAT instance generated by `bv_decide`, it can report a counterexample:
+  ```lean
+  /--
+  error: The prover found a counterexample, consider the following assignment:
+  x = 0xffffffffffffffff#64
+  -/
+  #guard_msgs in
+  example (x : BitVec 64) : x < x + 1 := by
+    bv_decide
+  ```
+
+  See `Lean.Elab.Tactic.BVDecide` for a more detailed overview, and look in `tests/lean/run/bv_*` for examples.
+
+  [#5013](https://github.com/leanprover/lean4/pull/5013), [#5074](https://github.com/leanprover/lean4/pull/5074), [#5100](https://github.com/leanprover/lean4/pull/5100), [#5113](https://github.com/leanprover/lean4/pull/5113), [#5137](https://github.com/leanprover/lean4/pull/5137), [#5203](https://github.com/leanprover/lean4/pull/5203), [#5212](https://github.com/leanprover/lean4/pull/5212), [#5220](https://github.com/leanprover/lean4/pull/5220).
+
+* `simp` tactic
+  * [#4988](https://github.com/leanprover/lean4/pull/4988) fixes a panic in the `reducePow` simproc.
+  * [#5071](https://github.com/leanprover/lean4/pull/5071) exposes the `index` option to the `dsimp` tactic, introduced to `simp` in [#4202](https://github.com/leanprover/lean4/pull/4202).
+  * [#5159](https://github.com/leanprover/lean4/pull/5159) fixes a panic at `Fin.isValue` simproc.
+  * [#5167](https://github.com/leanprover/lean4/pull/5167) and [#5175](https://github.com/leanprover/lean4/pull/5175) rename the `simpCtorEq` simproc to `reduceCtorEq` and makes it optional. (See breaking changes.)
+  * [#5187](https://github.com/leanprover/lean4/pull/5187) ensures `reduceCtorEq` is enabled in the `norm_cast` tactic.
+  * [#5073](https://github.com/leanprover/lean4/pull/5073) modifies the simp debug trace messages to tag with "dpre" and "dpost" instead of "pre" and "post" when in definitional rewrite mode. [#5054](https://github.com/leanprover/lean4/pull/5054) explains the `reduce` steps for `trace.Debug.Meta.Tactic.simp` trace messages.
+* `ext` tactic
+  * [#4996](https://github.com/leanprover/lean4/pull/4996) reduces default maximum iteration depth from 1000000 to 100.
+* `induction` tactic
+  * [#5117](https://github.com/leanprover/lean4/pull/5117) fixes a bug where `let` bindings in minor premises wouldn't be counted correctly.
+
+* `omega` tactic
+  * [#5157](https://github.com/leanprover/lean4/pull/5157) fixes a panic.
+
+* `conv` tactic
+  * [#5149](https://github.com/leanprover/lean4/pull/5149) improves `arg n` to handle subsingleton instance arguments.
+
+* [#5044](https://github.com/leanprover/lean4/pull/5044) upstreams the `#time` command.
+* [#5079](https://github.com/leanprover/lean4/pull/5079) makes `#check` and `#reduce` typecheck the elaborated terms.
+
+* **Incrementality**
+  * [#4974](https://github.com/leanprover/lean4/pull/4974) fixes regression where we would not interrupt elaboration of previous document versions.
+  * [#5004](https://github.com/leanprover/lean4/pull/5004) fixes a performance regression.
+  * [#5001](https://github.com/leanprover/lean4/pull/5001) disables incremental body elaboration in presence of `where` clauses in declarations.
+  * [#5018](https://github.com/leanprover/lean4/pull/5018) enables infotrees on the command line for ilean generation.
+  * [#5040](https://github.com/leanprover/lean4/pull/5040) and [#5056](https://github.com/leanprover/lean4/pull/5056) improve performance of info trees.
+  * [#5090](https://github.com/leanprover/lean4/pull/5090) disables incrementality in the `case .. | ..` tactic.
+  * [#5312](https://github.com/leanprover/lean4/pull/5312) fixes a bug where changing whitespace after the module header could break subsequent commands.
+
+* **Definitions**
+  * [#5016](https://github.com/leanprover/lean4/pull/5016) and [#5066](https://github.com/leanprover/lean4/pull/5066) add `clean_wf` tactic to clean up tactic state in `decreasing_by`. This can be disabled with `set_option debug.rawDecreasingByGoal false`.
+  * [#5055](https://github.com/leanprover/lean4/pull/5055) unifies equational theorems between structural and well-founded recursion.
+  * [#5041](https://github.com/leanprover/lean4/pull/5041) allows mutually recursive functions to use different parameter names among the “fixed parameter prefix”
+  * [#4154](https://github.com/leanprover/lean4/pull/4154) and [#5109](https://github.com/leanprover/lean4/pull/5109) add fine-grained equational lemmas for non-recursive functions. See breaking changes.
+  * [#5129](https://github.com/leanprover/lean4/pull/5129) unifies equation lemmas for recursive and non-recursive definitions. The `backward.eqns.deepRecursiveSplit` option can be set to `false` to get the old behavior. See breaking changes.
+  * [#5141](https://github.com/leanprover/lean4/pull/5141) adds `f.eq_unfold` lemmas. Now Lean produces the following zoo of rewrite rules:
+    ```
+    Option.map.eq_1      : Option.map f none = none
+    Option.map.eq_2      : Option.map f (some x) = some (f x)
+    Option.map.eq_def    : Option.map f p = match o with | none => none | (some x) => some (f x)
+    Option.map.eq_unfold : Option.map = fun f p => match o with | none => none | (some x) => some (f x)
+    ```
+    The `f.eq_unfold` variant is especially useful to rewrite with `rw` under binders.
+  * [#5136](https://github.com/leanprover/lean4/pull/5136) fixes bugs in recursion over predicates.
+
+* **Variable inclusion**
+  * [#5206](https://github.com/leanprover/lean4/pull/5206) documents that `include` currently only applies to theorems.
+
+* **Elaboration**
+  * [#4926](https://github.com/leanprover/lean4/pull/4926) fixes a bug where autoparam errors were associated to an incorrect source position.
+  * [#4833](https://github.com/leanprover/lean4/pull/4833) fixes an issue where cdot anonymous functions (e.g. `(· + ·)`) would not handle ambiguous notation correctly. Numbers the parameters, making this example expand as `fun x1 x2 => x1 + x2` rather than `fun x x_1 => x + x_1`.
+  * [#5037](https://github.com/leanprover/lean4/pull/5037) improves strength of the tactic that proves array indexing is in bounds.
+  * [#5119](https://github.com/leanprover/lean4/pull/5119) fixes a bug in the tactic that proves indexing is in bounds where it could loop in the presence of mvars.
+  * [#5072](https://github.com/leanprover/lean4/pull/5072) makes the structure type clickable in "not a field of structure" errors for structure instance notation.
+  * [#4717](https://github.com/leanprover/lean4/pull/4717) fixes a bug where mutual `inductive` commands could create terms that the kernel rejects.
+  * [#5142](https://github.com/leanprover/lean4/pull/5142) fixes a bug where `variable` could fail when mixing binder updates and declarations.
+
+* **Other fixes or improvements**
+  * [#5118](https://github.com/leanprover/lean4/pull/5118) changes the definition of the `syntheticHole` parser so that hovering over `_` in `?_` gives the docstring for synthetic holes.
+  * [#5173](https://github.com/leanprover/lean4/pull/5173) uses the emoji variant selector for ✅️,❌️,💥️ in messages, improving fonts selection.
+  * [#5183](https://github.com/leanprover/lean4/pull/5183) fixes a bug in `rename_i` where implementation detail hypotheses could be renamed.
+
+### Language server, widgets, and IDE extensions
+
+* [#4821](https://github.com/leanprover/lean4/pull/4821) resolves two language server bugs that especially affect Windows users. (1) Editing the header could result in the watchdog not correctly restarting the file worker, which would lead to the file seemingly being processed forever. (2) On an especially slow Windows machine, we found that starting the language server would sometimes not succeed at all. This PR also resolves an issue where we would not correctly emit messages that we received while the file worker is being restarted to the corresponding file worker after the restart.
+* [#5006](https://github.com/leanprover/lean4/pull/5006) updates the user widget manual.
+* [#5193](https://github.com/leanprover/lean4/pull/5193) updates the quickstart guide with the new display name for the Lean 4 extension ("Lean 4").
+* [#5185](https://github.com/leanprover/lean4/pull/5185) fixes a bug where over time "import out of date" messages would accumulate.
+* [#4900](https://github.com/leanprover/lean4/pull/4900) improves ilean loading performance by about a factor of two. Optimizes the JSON parser and the conversion from JSON to Lean data structures; see PR description for details.
+* **Other fixes or improvements**
+  * [#5031](https://github.com/leanprover/lean4/pull/5031) localizes an instance in `Lsp.Diagnostics`.
+
+### Pretty printing
+
+* [#4976](https://github.com/leanprover/lean4/pull/4976) introduces `@[app_delab]`, a macro for creating delaborators for particular constants. The `@[app_delab ident]` syntax resolves `ident` to its constant name `name` and then expands to `@[delab app.name]`.
+* [#4982](https://github.com/leanprover/lean4/pull/4982) fixes a bug where the pretty printer assumed structure projections were type correct (such terms can appear in type mismatch errors). Improves hoverability of `#print` output for structures.
+* [#5218](https://github.com/leanprover/lean4/pull/5218) and [#5239](https://github.com/leanprover/lean4/pull/5239) add `pp.exprSizes` debugging option. When true, each pretty printed expression is prefixed with `[size a/b/c]`, where `a` is the size without sharing, `b` is the actual size, and `c` is the size with the maximum possible sharing.
+
+### Library
+
+* [#5020](https://github.com/leanprover/lean4/pull/5020) swaps the parameters to `Membership.mem`. A purpose of this change is to make set-like `CoeSort` coercions to refer to the eta-expanded function `fun x => Membership.mem s x`, which can reduce in many computations. Another is that having the `s` argument first leads to better discrimination tree keys. (See breaking changes.)
+* `Array`
+  * [#4970](https://github.com/leanprover/lean4/pull/4970) adds `@[ext]` attribute to `Array.ext`.
+  * [#4957](https://github.com/leanprover/lean4/pull/4957) deprecates `Array.get_modify`.
+* `List`
+  * [#4995](https://github.com/leanprover/lean4/pull/4995) upstreams `List.findIdx` lemmas.
+  * [#5029](https://github.com/leanprover/lean4/pull/5029), [#5048](https://github.com/leanprover/lean4/pull/5048) and [#5132](https://github.com/leanprover/lean4/pull/5132) add `List.Sublist` lemmas, some upstreamed. [#5077](https://github.com/leanprover/lean4/pull/5077) fixes implicitness in refl/rfl lemma binders.  add `List.Sublist` theorems.
+  * [#5047](https://github.com/leanprover/lean4/pull/5047) upstreams `List.Pairwise` lemmas.
+  * [#5053](https://github.com/leanprover/lean4/pull/5053), [#5124](https://github.com/leanprover/lean4/pull/5124), and [#5161](https://github.com/leanprover/lean4/pull/5161) add `List.find?/findSome?/findIdx?` theorems.
+  * [#5039](https://github.com/leanprover/lean4/pull/5039) adds `List.foldlRecOn` and `List.foldrRecOn` recursion principles to prove things about `List.foldl` and `List.foldr`.
+  * [#5069](https://github.com/leanprover/lean4/pull/5069) upstreams `List.Perm`.
+  * [#5092](https://github.com/leanprover/lean4/pull/5092) and [#5107](https://github.com/leanprover/lean4/pull/5107) add `List.mergeSort` and a fast `@[csimp]` implementation.
+  * [#5103](https://github.com/leanprover/lean4/pull/5103) makes the simp lemmas for `List.subset` more aggressive.
+  * [#5106](https://github.com/leanprover/lean4/pull/5106) changes the statement of `List.getLast?_cons`.
+  * [#5123](https://github.com/leanprover/lean4/pull/5123) and [#5158](https://github.com/leanprover/lean4/pull/5158) add `List.range` and `List.iota` lemmas.
+  * [#5130](https://github.com/leanprover/lean4/pull/5130) adds `List.join` lemmas.
+  * [#5131](https://github.com/leanprover/lean4/pull/5131) adds `List.append` lemmas.
+  * [#5152](https://github.com/leanprover/lean4/pull/5152) adds `List.erase(|P|Idx)` lemmas.
+  * [#5127](https://github.com/leanprover/lean4/pull/5127) makes miscellaneous lemma updates.
+  * [#5153](https://github.com/leanprover/lean4/pull/5153) and [#5160](https://github.com/leanprover/lean4/pull/5160) add lemmas about `List.attach` and `List.pmap`.
+  * [#5164](https://github.com/leanprover/lean4/pull/5164), [#5177](https://github.com/leanprover/lean4/pull/5177), and [#5215](https://github.com/leanprover/lean4/pull/5215) add `List.find?` and `List.range'/range/iota` lemmas.
+  * [#5196](https://github.com/leanprover/lean4/pull/5196) adds `List.Pairwise_erase` and related lemmas.
+  * [#5151](https://github.com/leanprover/lean4/pull/5151) and [#5163](https://github.com/leanprover/lean4/pull/5163) improve confluence of `List` simp lemmas. [#5105](https://github.com/leanprover/lean4/pull/5105) and [#5102](https://github.com/leanprover/lean4/pull/5102) adjust `List` simp lemmas.
+  * [#5178](https://github.com/leanprover/lean4/pull/5178) removes `List.getLast_eq_iff_getLast_eq_some` as a simp lemma.
+  * [#5210](https://github.com/leanprover/lean4/pull/5210) reverses the meaning of `List.getElem_drop` and `List.getElem_drop'`.
+  * [#5214](https://github.com/leanprover/lean4/pull/5214) moves `@[csimp]` lemmas earlier where possible.
+* `Nat` and `Int`
+  * [#5104](https://github.com/leanprover/lean4/pull/5104) adds `Nat.add_left_eq_self` and relatives.
+  * [#5146](https://github.com/leanprover/lean4/pull/5146) adds missing `Nat.and_xor_distrib_(left|right)`.
+  * [#5148](https://github.com/leanprover/lean4/pull/5148) and [#5190](https://github.com/leanprover/lean4/pull/5190) improve `Nat` and `Int` simp lemma confluence.
+  * [#5165](https://github.com/leanprover/lean4/pull/5165) adjusts `Int` simp lemmas.
+  * [#5166](https://github.com/leanprover/lean4/pull/5166) adds `Int` lemmas relating `neg` and `emod`/`mod`.
+  * [#5208](https://github.com/leanprover/lean4/pull/5208) reverses the direction of the `Int.toNat_sub` simp lemma.
+  * [#5209](https://github.com/leanprover/lean4/pull/5209) adds `Nat.bitwise` lemmas.
+  * [#5230](https://github.com/leanprover/lean4/pull/5230) corrects the docstrings for integer division and modulus.
+* `Option`
+  * [#5128](https://github.com/leanprover/lean4/pull/5128) and [#5154](https://github.com/leanprover/lean4/pull/5154) add `Option` lemmas.
+* `BitVec`
+  * [#4889](https://github.com/leanprover/lean4/pull/4889) adds `sshiftRight` bitblasting.
+  * [#4981](https://github.com/leanprover/lean4/pull/4981) adds `Std.Associative` and `Std.Commutative` instances for `BitVec.[and|or|xor]`.
+  * [#4913](https://github.com/leanprover/lean4/pull/4913) enables `missingDocs` error for `BitVec` modules.
+  * [#4930](https://github.com/leanprover/lean4/pull/4930) makes parameter names for `BitVec` more consistent.
+  * [#5098](https://github.com/leanprover/lean4/pull/5098) adds `BitVec.intMin`. Introduces `boolToPropSimps` simp set for converting from boolean to propositional expressions.
+  * [#5200](https://github.com/leanprover/lean4/pull/5200) and [#5217](https://github.com/leanprover/lean4/pull/5217) rename `BitVec.getLsb` to `BitVec.getLsbD`, etc., to bring naming in line with `List`/`Array`/etc.
+  * **Theorems:** [#4977](https://github.com/leanprover/lean4/pull/4977), [#4951](https://github.com/leanprover/lean4/pull/4951), [#4667](https://github.com/leanprover/lean4/pull/4667), [#5007](https://github.com/leanprover/lean4/pull/5007), [#4997](https://github.com/leanprover/lean4/pull/4997), [#5083](https://github.com/leanprover/lean4/pull/5083), [#5081](https://github.com/leanprover/lean4/pull/5081), [#4392](https://github.com/leanprover/lean4/pull/4392)
+* `UInt`
+  * [#4514](https://github.com/leanprover/lean4/pull/4514) fixes naming convention for `UInt` lemmas.
+* `Std.HashMap` and `Std.HashSet`
+  * [#4943](https://github.com/leanprover/lean4/pull/4943) deprecates variants of hash map query methods. (See breaking changes.)
+  * [#4917](https://github.com/leanprover/lean4/pull/4917) switches the library and Lean to `Std.HashMap` and `Std.HashSet` almost everywhere.
+  * [#4954](https://github.com/leanprover/lean4/pull/4954) deprecates `Lean.HashMap` and `Lean.HashSet`.
+  * [#5023](https://github.com/leanprover/lean4/pull/5023) cleans up lemma parameters.
+
+* `Std.Sat` (for `bv_decide`)
+  * [#4933](https://github.com/leanprover/lean4/pull/4933) adds definitions of SAT and CNF.
+  * [#4953](https://github.com/leanprover/lean4/pull/4953) defines "and-inverter graphs" (AIGs) as described in section 3 of [Davis-Swords 2013](https://arxiv.org/pdf/1304.7861.pdf).
+
+* **Parsec**
+  * [#4774](https://github.com/leanprover/lean4/pull/4774) generalizes the `Parsec` library, allowing parsing of iterable data beyond `String` such as `ByteArray`. (See breaking changes.)
+  * [#5115](https://github.com/leanprover/lean4/pull/5115) moves `Lean.Data.Parsec` to `Std.Internal.Parsec` for bootstrappng reasons.
+
+* `Thunk`
+  * [#4969](https://github.com/leanprover/lean4/pull/4969) upstreams `Thunk.ext`.
+
+* **IO**
+  * [#4973](https://github.com/leanprover/lean4/pull/4973) modifies `IO.FS.lines` to handle `\r\n` on all operating systems instead of just on Windows.
+  * [#5125](https://github.com/leanprover/lean4/pull/5125) adds `createTempFile` and `withTempFile` for creating temporary files that can only be read and written by the current user.
+
+* **Other fixes or improvements**
+  * [#4945](https://github.com/leanprover/lean4/pull/4945) adds `Array`, `Bool` and `Prod` utilities from LeanSAT.
+  * [#4960](https://github.com/leanprover/lean4/pull/4960) adds `Relation.TransGen.trans`.
+  * [#5012](https://github.com/leanprover/lean4/pull/5012) states `WellFoundedRelation Nat` using `<`, not `Nat.lt`.
+  * [#5011](https://github.com/leanprover/lean4/pull/5011) uses `≠` instead of `Not (Eq ...)` in `Fin.ne_of_val_ne`.
+  * [#5197](https://github.com/leanprover/lean4/pull/5197) upstreams `Fin.le_antisymm`.
+  * [#5042](https://github.com/leanprover/lean4/pull/5042) reduces usage of `refine'`.
+  * [#5101](https://github.com/leanprover/lean4/pull/5101) adds about `if-then-else` and `Option`.
+  * [#5112](https://github.com/leanprover/lean4/pull/5112) adds basic instances for `ULift` and `PLift`.
+  * [#5133](https://github.com/leanprover/lean4/pull/5133) and [#5168](https://github.com/leanprover/lean4/pull/5168) make fixes from running the simpNF linter over Lean.
+  * [#5156](https://github.com/leanprover/lean4/pull/5156) removes a bad simp lemma in `omega` theory.
+  * [#5155](https://github.com/leanprover/lean4/pull/5155) improves confluence of `Bool` simp lemmas.
+  * [#5162](https://github.com/leanprover/lean4/pull/5162) improves confluence of `Function.comp` simp lemmas.
+  * [#5191](https://github.com/leanprover/lean4/pull/5191) improves confluence of `if-then-else` simp lemmas.
+  * [#5147](https://github.com/leanprover/lean4/pull/5147) adds `@[elab_as_elim]` to `Quot.rec`, `Nat.strongInductionOn` and `Nat.casesStrongInductionOn`, and also renames the latter two to `Nat.strongRecOn` and `Nat.casesStrongRecOn` (deprecated in [#5179](https://github.com/leanprover/lean4/pull/5179)).
+  * [#5180](https://github.com/leanprover/lean4/pull/5180) disables some simp lemmas with bad discrimination tree keys.
+  * [#5189](https://github.com/leanprover/lean4/pull/5189) cleans up internal simp lemmas that had leaked.
+  * [#5198](https://github.com/leanprover/lean4/pull/5198) cleans up `allowUnsafeReducibility`.
+  * [#5229](https://github.com/leanprover/lean4/pull/5229) removes unused lemmas from some `simp` tactics.
+  * [#5199](https://github.com/leanprover/lean4/pull/5199) removes >6 month deprecations.
+
+### Lean internals
+
+* **Performance**
+  * Some core algorithms have been rewritten in C++ for performance.
+    * [#4910](https://github.com/leanprover/lean4/pull/4910) and [#4912](https://github.com/leanprover/lean4/pull/4912) reimplement `instantiateLevelMVars`.
+    * [#4915](https://github.com/leanprover/lean4/pull/4915), [#4922](https://github.com/leanprover/lean4/pull/4922), and [#4931](https://github.com/leanprover/lean4/pull/4931) reimplement `instantiateExprMVars`, 30% faster on a benchmark.
+  * [#4934](https://github.com/leanprover/lean4/pull/4934) has optimizations for the kernel's `Expr` equality test.
+  * [#4990](https://github.com/leanprover/lean4/pull/4990) fixes bug in hashing for the kernel's `Expr` equality test.
+  * [#4935](https://github.com/leanprover/lean4/pull/4935) and [#4936](https://github.com/leanprover/lean4/pull/4936) skip some `PreDefinition` transformations if they are not needed.
+  * [#5225](https://github.com/leanprover/lean4/pull/5225) adds caching for visited exprs at `CheckAssignmentQuick` in `ExprDefEq`.
+  * [#5226](https://github.com/leanprover/lean4/pull/5226) maximizes term sharing at `instantiateMVarDeclMVars`, used by `runTactic`.
+* **Diagnostics and profiling**
+  * [#4923](https://github.com/leanprover/lean4/pull/4923) adds profiling for `instantiateMVars` in `Lean.Elab.MutualDef`, which can be a bottleneck there.
+  * [#4924](https://github.com/leanprover/lean4/pull/4924) adds diagnostics for large theorems, controlled by the `diagnostics.threshold.proofSize` option.
+  * [#4897](https://github.com/leanprover/lean4/pull/4897) improves display of diagnostic results.
+* **Other fixes or improvements**
+  * [#4921](https://github.com/leanprover/lean4/pull/4921) cleans up `Expr.betaRev`.
+  * [#4940](https://github.com/leanprover/lean4/pull/4940) fixes tests by not writing directly to stdout, which is unreliable now that elaboration and reporting are executed in separate threads.
+  * [#4955](https://github.com/leanprover/lean4/pull/4955) documents that `stderrAsMessages` is now the default on the command line as well.
+  * [#4647](https://github.com/leanprover/lean4/pull/4647) adjusts documentation for building on macOS.
+  * [#4987](https://github.com/leanprover/lean4/pull/4987) makes regular mvar assignments take precedence over delayed ones in `instantiateMVars`. Normally delayed assignment metavariables are never directly assigned, but on errors Lean assigns `sorry` to unassigned metavariables.
+  * [#4967](https://github.com/leanprover/lean4/pull/4967) adds linter name to errors when a linter crashes.
+  * [#5043](https://github.com/leanprover/lean4/pull/5043) cleans up command line snapshots logic.
+  * [#5067](https://github.com/leanprover/lean4/pull/5067) minimizes some imports.
+  * [#5068](https://github.com/leanprover/lean4/pull/5068) generalizes the monad for `addMatcherInfo`.
+  * [f71a1f](https://github.com/leanprover/lean4/commit/f71a1fb4ae958fccb3ad4d48786a8f47ced05c15) adds missing test for [#5126](https://github.com/leanprover/lean4/issues/5126).
+  * [#5201](https://github.com/leanprover/lean4/pull/5201) restores a test.
+  * [#3698](https://github.com/leanprover/lean4/pull/3698) fixes a bug where label attributes did not pass on the attribute kind.
+  * Typos: [#5080](https://github.com/leanprover/lean4/pull/5080), [#5150](https://github.com/leanprover/lean4/pull/5150), [#5202](https://github.com/leanprover/lean4/pull/5202)
+
+### Compiler, runtime, and FFI
+
+* [#3106](https://github.com/leanprover/lean4/pull/3106) moves frontend to new snapshot architecture. Note that `Frontend.processCommand` and `FrontendM` are no longer used by Lean core, but they will be preserved.
+* [#4919](https://github.com/leanprover/lean4/pull/4919) adds missing include in runtime for `AUTO_THREAD_FINALIZATION` feature on Windows.
+* [#4941](https://github.com/leanprover/lean4/pull/4941) adds more `LEAN_EXPORT`s for Windows.
+* [#4911](https://github.com/leanprover/lean4/pull/4911) improves formatting of CLI help text for the frontend.
+* [#4950](https://github.com/leanprover/lean4/pull/4950) improves file reading and writing.
+  * `readBinFile` and `readFile` now only require two system calls (`stat` + `read`) instead of one `read` per 1024 byte chunk.
+  * `Handle.getLine` and `Handle.putStr` no longer get tripped up by NUL characters.
+* [#4971](https://github.com/leanprover/lean4/pull/4971) handles the SIGBUS signal when detecting stack overflows.
+* [#5062](https://github.com/leanprover/lean4/pull/5062) avoids overwriting existing signal handlers, like in [rust-lang/rust#69685](https://github.com/rust-lang/rust/pull/69685).
+* [#4860](https://github.com/leanprover/lean4/pull/4860) improves workarounds for building on Windows. Splits `libleanshared` on Windows to avoid symbol limit, removes the `LEAN_EXPORT` denylist workaround, adds missing `LEAN_EXPORT`s.
+* [#4952](https://github.com/leanprover/lean4/pull/4952) output panics into Lean's redirected stderr, ensuring panics ARE visible as regular messages in the language server and properly ordered in relation to other messages on the command line.
+* [#4963](https://github.com/leanprover/lean4/pull/4963) links LibUV.
+
+### Lake
+
+* [#5030](https://github.com/leanprover/lean4/pull/5030) removes dead code.
+* [#4770](https://github.com/leanprover/lean4/pull/4770) adds additional fields to the package configuration which will be used by Reservoir. See the PR description for details.
+
+
+### DevOps/CI
+* [#4914](https://github.com/leanprover/lean4/pull/4914) and [#4937](https://github.com/leanprover/lean4/pull/4937) improve the release checklist.
+* [#4925](https://github.com/leanprover/lean4/pull/4925) ignores stale leanpkg tests.
+* [#5003](https://github.com/leanprover/lean4/pull/5003) upgrades `actions/cache` in CI.
+* [#5010](https://github.com/leanprover/lean4/pull/5010) sets `save-always` in cache actions in CI.
+* [#5008](https://github.com/leanprover/lean4/pull/5008) adds more libuv search patterns for the speedcenter.
+* [#5009](https://github.com/leanprover/lean4/pull/5009) reduce number of runs in the speedcenter for "fast" benchmarks from 10 to 3.
+* [#5014](https://github.com/leanprover/lean4/pull/5014) adjusts lakefile editing to use new `git` syntax in `pr-release` workflow.
+* [#5025](https://github.com/leanprover/lean4/pull/5025) has `pr-release` workflow pass `--retry` to `curl`.
+* [#5022](https://github.com/leanprover/lean4/pull/5022) builds MacOS Aarch64 release for PRs by default.
+* [#5045](https://github.com/leanprover/lean4/pull/5045) adds libuv to the required packages heading in macos docs.
+* [#5034](https://github.com/leanprover/lean4/pull/5034) fixes the install name of `libleanshared_1` on macOS.
+* [#5051](https://github.com/leanprover/lean4/pull/5051) fixes Windows stage 0.
+* [#5052](https://github.com/leanprover/lean4/pull/5052) fixes 32bit stage 0 builds in CI.
+* [#5057](https://github.com/leanprover/lean4/pull/5057) avoids rebuilding `leanmanifest` in each build.
+* [#5099](https://github.com/leanprover/lean4/pull/5099) makes `restart-on-label` workflow also filter by commit SHA.
+* [#4325](https://github.com/leanprover/lean4/pull/4325) adds CaDiCaL.
+
+### Breaking changes
+
+* [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. ([#4963](https://github.com/leanprover/lean4/pull/4963))
+
+* Recursive definitions with a `decreasing_by` clause that begins with `simp_wf` may break. Try removing `simp_wf` or replacing it with `simp`. ([#5016](https://github.com/leanprover/lean4/pull/5016))
+
+* The behavior of `rw [f]` where `f` is a non-recursive function defined by pattern matching changed.
+
+  For example, preciously, `rw [Option.map]` would rewrite `Option.map f o` to `match o with … `. Now this rewrite fails because it will use the equational lemmas, and these require constructors – just like for `List.map`.
+
+  Remedies:
+  * Split on `o` before rewriting.
+  * Use `rw [Option.map.eq_def]`, which rewrites any (saturated) application of `Option.map`.
+  * Use `set_option backward.eqns.nonrecursive false` when *defining* the function in question.
+  ([#4154](https://github.com/leanprover/lean4/pull/4154))
+
+* The unified handling of equation lemmas for recursive and non-recursive functions can break existing code, as there now can be extra equational lemmas:
+
+  * Explicit uses of `f.eq_2` might have to be adjusted if the numbering changed.
+
+  * Uses of `rw [f]` or `simp [f]` may no longer apply if they previously matched (and introduced a `match` statement), when the equational lemmas got more fine-grained.
+
+    In this case either case analysis on the parameters before rewriting helps, or setting the option `backward.eqns.deepRecursiveSplit false` while *defining* the function.
+
+  ([#5129](https://github.com/leanprover/lean4/pull/5129), [#5207](https://github.com/leanprover/lean4/pull/5207))
+
+* The `reduceCtorEq` simproc is now optional, and it might need to be included in lists of simp lemmas, like `simp only [reduceCtorEq]`. This simproc is responsible for reducing equalities of constructors. ([#5167](https://github.com/leanprover/lean4/pull/5167))
+
+* `Nat.strongInductionOn` is now `Nat.strongRecOn` and `Nat.caseStrongInductionOn` to `Nat.caseStrongRecOn`. ([#5147](https://github.com/leanprover/lean4/pull/5147))
+
+* The parameters to `Membership.mem` have been swapped, which affects all `Membership` instances. ([#5020](https://github.com/leanprover/lean4/pull/5020))
+
+* The meanings of `List.getElem_drop` and `List.getElem_drop'` have been reversed and the first is now a simp lemma. ([#5210](https://github.com/leanprover/lean4/pull/5210))
+
+* The `Parsec` library has moved from `Lean.Data.Parsec` to `Std.Internal.Parsec`. The `Parsec` type is now more general with a parameter for an iterable. Users parsing strings can migrate to `Parser` in the `Std.Internal.Parsec.String` namespace, which also includes string-focused parsing combinators. ([#4774](https://github.com/leanprover/lean4/pull/4774))
+
+* The `Lean` module has switched from `Lean.HashMap` and `Lean.HashSet` to `Std.HashMap` and `Std.HashSet` ([#4943](https://github.com/leanprover/lean4/pull/4943)). `Lean.HashMap` and `Lean.HashSet` are now deprecated ([#4954](https://github.com/leanprover/lean4/pull/4954)) 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 changes from `Lean.HashMap` to `Std.HashMap`:
+  * query functions use the term `get` instead of `find`, ([#4943](https://github.com/leanprover/lean4/pull/4943))
+  * the notation `map[key]` no longer returns an optional value but instead expects a proof that the key is present in the map. The previous behavior is available via the `map[key]?` notation.
+
 
 v4.11.0
 ----------
@@ -21,7 +654,7 @@ v4.11.0
 
   See breaking changes below.
 
-  PRs: [#4883](https://github.com/leanprover/lean4/pull/4883), [1242ff](https://github.com/leanprover/lean4/commit/1242ffbfb5a79296041683682268e770fc3cf820), [#5000](https://github.com/leanprover/lean4/pull/5000), [#5036](https://github.com/leanprover/lean4/pull/5036), [#5138](https://github.com/leanprover/lean4/pull/5138), [0edf1b](https://github.com/leanprover/lean4/commit/0edf1bac392f7e2fe0266b28b51c498306363a84).
+  PRs: [#4883](https://github.com/leanprover/lean4/pull/4883), [#4814](https://github.com/leanprover/lean4/pull/4814), [#5000](https://github.com/leanprover/lean4/pull/5000), [#5036](https://github.com/leanprover/lean4/pull/5036), [#5138](https://github.com/leanprover/lean4/pull/5138), [0edf1b](https://github.com/leanprover/lean4/commit/0edf1bac392f7e2fe0266b28b51c498306363a84).
 
 * **Recursive definitions**
   * Structural recursion can now be explicitly requested using

doc/make/index.md

@@ -1,6 +1,6 @@
-These are instructions to set up a working development environment for those who wish to make changes to Lean itself. It is part of the [Development Guide](doc/dev/index.md).
+These are instructions to set up a working development environment for those who wish to make changes to Lean itself. It is part of the [Development Guide](../dev/index.md).
 
-We strongly suggest that new users instead follow the [Quickstart](doc/quickstart.md) to get started using Lean, since this sets up an environment that can automatically manage multiple Lean toolchain versions, which is necessary when working within the Lean ecosystem.
+We strongly suggest that new users instead follow the [Quickstart](../quickstart.md) to get started using Lean, since this sets up an environment that can automatically manage multiple Lean toolchain versions, which is necessary when working within the Lean ecosystem.
 
 Requirements
 ------------

doc/make/msys2.md

@@ -15,17 +15,24 @@ Mode](https://docs.microsoft.com/en-us/windows/apps/get-started/enable-your-devi
 which will allow Lean to create symlinks that e.g. enable go-to-definition in
 the stdlib.
 
+## Installing the Windows SDK
+
+Install the Windows SDK from [Microsoft](https://developer.microsoft.com/en-us/windows/downloads/windows-sdk/).
+The oldest supported version is 10.0.18362.0. If you installed the Windows SDK to the default location,
+then there should be a directory with the version number at `C:\Program Files (x86)\Windows Kits\10\Include`.
+If there are multiple directories, only the highest version number matters.
+
 ## Installing dependencies
 
 [The official webpage of MSYS2][msys2] provides one-click installers.
-Once installed, you should run the "MSYS2 MinGW 64-bit shell" from the start menu (the one that runs `mingw64.exe`).
-Do not run "MSYS2 MSYS" instead!
-MSYS2 has a package management system, [pacman][pacman], which is used in Arch Linux.
+Once installed, you should run the "MSYS2 CLANG64" shell from the start menu (the one that runs `clang64.exe`).
+Do not run "MSYS2 MSYS" or "MSYS2 MINGW64" instead!
+MSYS2 has a package management system, [pacman][pacman].
 
 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 mingw-w64-x86_64-libuv mingw-w64-x86_64-gmp git unzip diffutils binutils
+pacman -S make python mingw-w64-clang-x86_64-cmake mingw-w64-clang-x86_64-clang mingw-w64-clang-x86_64-ccache mingw-w64-clang-x86_64-libuv mingw-w64-clang-x86_64-gmp git unzip diffutils binutils
 ```
 
 You should now be able to run these commands:
@@ -61,8 +68,7 @@ If you want a version that can run independently of your MSYS install
 then you need to copy the following dependent DLL's from where ever
 they are installed in your MSYS setup:
 
-- libgcc_s_seh-1.dll
-- libstdc++-6.dll
+- libc++.dll
 - libgmp-10.dll
 - libuv-1.dll
 - libwinpthread-1.dll
@@ -82,6 +88,6 @@ version clang to your path.
 
 **-bash: gcc: command not found**
 
-Make sure `/mingw64/bin` is in your PATH environment.  If it is not then
-check you launched the MSYS2 MinGW 64-bit shell from the start menu.
-(The one that runs `mingw64.exe`).
+Make sure `/clang64/bin` is in your PATH environment.  If it is not then
+check you launched the MSYS2 CLANG64 shell from the start menu.
+(The one that runs `clang64.exe`).

doc/monads/applicatives.lean

@@ -138,8 +138,8 @@ definition:
 
 -/
 instance : Applicative List where
-  pure := List.pure
-  seq f x := List.bind f fun y => Functor.map y (x ())
+  pure := List.singleton
+  seq f x := List.flatMap f fun y => Functor.map y (x ())
 /-!
 
 Notice you can now sequence a _list_ of functions and a _list_ of items.

doc/monads/laws.lean

@@ -128,8 +128,8 @@ Applying the identity function through an applicative structure should not chang
 values or structure.  For example:
 -/
 instance : Applicative List where
-  pure := List.pure
-  seq f x := List.bind f fun y => Functor.map y (x ())
+  pure := List.singleton
+  seq f x := List.flatMap f fun y => Functor.map y (x ())
 
 #eval pure id <*> [1, 2, 3]  -- [1, 2, 3]
 /-!
@@ -235,8 +235,8 @@ structure or its values.
 Left identity is `x >>= pure = x` and is demonstrated by the following examples on a monadic `List`:
 -/
 instance : Monad List  where
-  pure := List.pure
-  bind := List.bind
+  pure := List.singleton
+  bind := List.flatMap
 
 def a := ["apple", "orange"]
 

doc/monads/monads.lean

@@ -192,8 +192,8 @@ implementation of `pure` and `bind`.
 
 -/
 instance : Monad List  where
-  pure := List.pure
-  bind := List.bind
+  pure := List.singleton
+  bind := List.flatMap
 /-!
 
 Like you saw with the applicative `seq` operator, the `bind` operator applies the given function

doc/setup.md

@@ -7,7 +7,7 @@ Platforms built & tested by our CI, available as binary releases via elan (see b
 * x86-64 Linux with glibc 2.27+
 * x86-64 macOS 10.15+
 * aarch64 (Apple Silicon) macOS 10.15+
-* x86-64 Windows 10+
+* x86-64 Windows 11 (any version), Windows 10 (version 1903 or higher), Windows Server 2022
 
 ### Tier 2
 

flake.nix

@@ -38,8 +38,24 @@
           # more convenient `ctest` output
           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"]; });
+          GMP = (pkgsDist.gmp.override { withStatic = true; }).overrideAttrs (attrs:
+            pkgs.lib.optionalAttrs (pkgs.stdenv.system == "aarch64-linux") {
+              # would need additional linking setup on Linux aarch64, we don't use it anywhere else either
+              hardeningDisable = [ "stackprotector" ];
+            });
+          LIBUV = pkgsDist.libuv.overrideAttrs (attrs: {
+            configureFlags = ["--enable-static"];
+            hardeningDisable = [ "stackprotector" ];
+            # Sync version with CMakeLists.txt
+            version = "1.48.0";
+            src = pkgs.fetchFromGitHub {
+              owner = "libuv";
+              repo = "libuv";
+              rev = "v1.48.0";
+              sha256 = "100nj16fg8922qg4m2hdjh62zv4p32wyrllsvqr659hdhjc03bsk";
+            };
+            doCheck = false;
+          });
           GLIBC = pkgsDist.glibc;
           GLIBC_DEV = pkgsDist.glibc.dev;
           GCC_LIB = pkgsDist.gcc.cc.lib;

releases_drafts/hashmap.md

@@ -1,3 +0,0 @@
-* 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

@@ -1 +0,0 @@
-* #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.

script/prepare-llvm-linux.sh

@@ -48,6 +48,8 @@ $CP llvm-host/lib/*/lib{c++,c++abi,unwind}.* llvm-host/lib/
 $CP -r llvm/include/*-*-* llvm-host/include/
 # glibc: use for linking (so Lean programs don't embed newer symbol versions), but not for running (because libc.so, librt.so, and ld.so must be compatible)!
 $CP $GLIBC/lib/libc_nonshared.a stage1/lib/glibc
+# libpthread_nonshared.a must be linked in order to be able to use `pthread_atfork(3)`. LibUV uses this function.
+$CP $GLIBC/lib/libpthread_nonshared.a stage1/lib/glibc
 for f in $GLIBC/lib/lib{c,dl,m,rt,pthread}-*; do b=$(basename $f); cp $f stage1/lib/glibc/${b%-*}.so; done
 OPTIONS=()
 echo -n " -DLEAN_STANDALONE=ON"
@@ -62,8 +64,8 @@ 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 -luv -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 ROOT/lib/glibc/libpthread_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 -luv -Wl,--no-as-needed'"
+echo -n " -DLEAN_EXTRA_LINKER_FLAGS='-Wl,--as-needed -lgmp -luv -lpthread -ldl -lrt -Wl,--no-as-needed'"
 # do not set `LEAN_CC` for tests
 echo -n " -DLEAN_TEST_VARS=''"

script/prepare-llvm-mingw.sh

@@ -31,15 +31,21 @@ 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 /clang64/lib/libuv.a llvm/lib/lib{c++,c++abi,unwind}.a stage1/lib/
+# Note: even though we're linking against libraries like `libbcrypt.a` which appear to be static libraries from the file name,
+# we're not actually linking statically against the code.
+# Rather, `libbcrypt.a` is an import library (see https://en.wikipedia.org/wiki/Dynamic-link_library#Import_libraries) that just
+# tells the compiler how to dynamically link against `bcrypt.dll` (which is located in the System32 folder).
+# This distinction is relevant specifically for `libicu.a`/`icu.dll` because there we want updates to the time zone database to
+# be delivered to users via Windows Update without having to recompile Lean or Lean programs.
+cp /clang64/lib/lib{m,bcrypt,mingw32,moldname,mingwex,msvcrt,pthread,advapi32,shell32,user32,kernel32,ucrtbase,psapi,iphlpapi,userenv,ws2_32,dbghelp,ole32,icu}.* /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 -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 -luv -lucrtbase'"
+echo -n " -DLEANC_INTERNAL_LINKER_FLAGS='-L ROOT/lib -static-libgcc -Wl,-Bstatic -lgmp $(pkg-config --static --libs libuv) -lunwind -Wl,-Bdynamic -fuse-ld=lld'"
+# when not using the above flags, link GMP dynamically/as usual. Always link ICU dynamically.
+echo -n " -DLEAN_EXTRA_LINKER_FLAGS='-lgmp $(pkg-config --libs libuv) -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

@@ -10,13 +10,15 @@ endif()
 include(ExternalProject)
 project(LEAN CXX C)
 set(LEAN_VERSION_MAJOR 4)
-set(LEAN_VERSION_MINOR 12)
+set(LEAN_VERSION_MINOR 15)
 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'")
 set(LEAN_VERSION_STRING "${LEAN_VERSION_MAJOR}.${LEAN_VERSION_MINOR}.${LEAN_VERSION_PATCH}")
 if (LEAN_SPECIAL_VERSION_DESC)
   string(APPEND LEAN_VERSION_STRING "-${LEAN_SPECIAL_VERSION_DESC}")
+elseif (NOT LEAN_VERSION_IS_RELEASE)
+  string(APPEND LEAN_VERSION_STRING "-pre")
 endif()
 
 set(LEAN_PLATFORM_TARGET "" CACHE STRING "LLVM triple of the target platform")
@@ -155,6 +157,10 @@ endif ()
 # We want explicit stack probes in huge Lean stack frames for robust stack overflow detection
 string(APPEND LEANC_EXTRA_FLAGS " -fstack-clash-protection")
 
+# This makes signed integer overflow guaranteed to match 2's complement.
+string(APPEND CMAKE_CXX_FLAGS " -fwrapv")
+string(APPEND LEANC_EXTRA_FLAGS " -fwrapv")
+
 if(NOT MULTI_THREAD)
   message(STATUS "Disabled multi-thread support, it will not be safe to run multiple threads in parallel")
   set(AUTO_THREAD_FINALIZATION OFF)
@@ -243,15 +249,77 @@ if("${USE_GMP}" MATCHES "ON")
   endif()
 endif()
 
-if(NOT "${CMAKE_SYSTEM_NAME}" MATCHES "Emscripten")
-  # LibUV
+# LibUV
+if("${CMAKE_SYSTEM_NAME}" MATCHES "Emscripten")
+  # Only on WebAssembly we compile LibUV ourselves
+  set(LIBUV_EMSCRIPTEN_FLAGS "${EMSCRIPTEN_SETTINGS}")
+
+  # LibUV does not compile on WebAssembly without modifications because
+  # building LibUV on a platform requires including stub implementations
+  # for features not present on the target platform. This patch includes
+  # the minimum amount of stub implementations needed for successfully
+  # running Lean on WebAssembly and using LibUV's temporary file support.
+  # It still leaves several symbols completely undefined: uv__fs_event_close,
+  # uv__hrtime, uv__io_check_fd, uv__io_fork, uv__io_poll, uv__platform_invalidate_fd
+  # uv__platform_loop_delete, uv__platform_loop_init. Making additional
+  # LibUV features available on WebAssembly might require adapting the
+  # patch to include additional LibUV source files.
+  set(LIBUV_PATCH_IN "
+diff --git a/CMakeLists.txt b/CMakeLists.txt
+index 5e8e0166..f3b29134 100644
+--- a/CMakeLists.txt
++++ b/CMakeLists.txt
+@@ -317,6 +317,11 @@ if(CMAKE_SYSTEM_NAME STREQUAL \"GNU\")
+        src/unix/hurd.c)
+ endif()
+
++if(CMAKE_SYSTEM_NAME STREQUAL \"Emscripten\")
++  list(APPEND uv_sources
++       src/unix/no-proctitle.c)
++endif()
++
+ if(CMAKE_SYSTEM_NAME STREQUAL \"Linux\")
+   list(APPEND uv_defines _GNU_SOURCE _POSIX_C_SOURCE=200112)
+   list(APPEND uv_libraries dl rt)
+")
+  string(REPLACE "\n" "\\n" LIBUV_PATCH ${LIBUV_PATCH_IN})
+
+  ExternalProject_add(libuv
+    PREFIX libuv
+    GIT_REPOSITORY https://github.com/libuv/libuv
+    # Sync version with flake.nix
+    GIT_TAG v1.48.0
+    CMAKE_ARGS -DCMAKE_BUILD_TYPE=Release -DLIBUV_BUILD_TESTS=OFF -DLIBUV_BUILD_SHARED=OFF -DCMAKE_AR=${CMAKE_AR} -DCMAKE_TOOLCHAIN_FILE=${CMAKE_TOOLCHAIN_FILE} -DCMAKE_POSITION_INDEPENDENT_CODE=ON -DCMAKE_C_FLAGS=${LIBUV_EMSCRIPTEN_FLAGS}
+	  PATCH_COMMAND git reset --hard HEAD && printf "${LIBUV_PATCH}" > patch.diff && git apply patch.diff
+    BUILD_IN_SOURCE ON
+    INSTALL_COMMAND "")
+  set(LIBUV_INCLUDE_DIR "${CMAKE_BINARY_DIR}/libuv/src/libuv/include")
+  set(LIBUV_LIBRARIES "${CMAKE_BINARY_DIR}/libuv/src/libuv/libuv.a")
+else()
   find_package(LibUV 1.0.0 REQUIRED)
-  include_directories(${LIBUV_INCLUDE_DIR})
 endif()
+include_directories(${LIBUV_INCLUDE_DIR})
 if(NOT LEAN_STANDALONE)
   string(APPEND LEAN_EXTRA_LINKER_FLAGS " ${LIBUV_LIBRARIES}")
 endif()
 
+# Windows SDK (for ICU)
+if(${CMAKE_SYSTEM_NAME} MATCHES "Windows")
+  # Pass 'tools' to skip MSVC version check (as MSVC/Visual Studio is not necessarily installed)
+  find_package(WindowsSDK REQUIRED COMPONENTS tools)
+
+  # This will give a semicolon-separated list of include directories
+  get_windowssdk_include_dirs(${WINDOWSSDK_LATEST_DIR} WINDOWSSDK_INCLUDE_DIRS)
+
+  # To successfully build against Windows SDK headers, the Windows SDK headers must have lower
+  # priority than other system headers, so use `-idirafter`. Unfortunately, CMake does not
+  # support this using `include_directories`.
+  string(REPLACE ";" "\" -idirafter \"" WINDOWSSDK_INCLUDE_DIRS "${WINDOWSSDK_INCLUDE_DIRS}")
+  string(APPEND CMAKE_CXX_FLAGS " -idirafter \"${WINDOWSSDK_INCLUDE_DIRS}\"")
+
+  string(APPEND LEAN_EXTRA_LINKER_FLAGS " -licu")
+endif()
+
 # ccache
 if(CCACHE AND NOT CMAKE_CXX_COMPILER_LAUNCHER AND NOT CMAKE_C_COMPILER_LAUNCHER)
   find_program(CCACHE_PATH ccache)
@@ -435,7 +503,7 @@ endif()
 # Git HASH
 if(USE_GITHASH)
   include(GetGitRevisionDescription)
-  get_git_head_revision(GIT_REFSPEC GIT_SHA1)
+  get_git_head_revision(GIT_REFSPEC GIT_SHA1 ALLOW_LOOKING_ABOVE_CMAKE_SOURCE_DIR)
   if(${GIT_SHA1} MATCHES "GITDIR-NOTFOUND")
     message(STATUS "Failed to read git_sha1")
     set(GIT_SHA1 "")
@@ -522,6 +590,10 @@ if(${STAGE} GREATER 1)
   endif()
 else()
   add_subdirectory(runtime)
+  if("${CMAKE_SYSTEM_NAME}" MATCHES "Emscripten")
+    add_dependencies(leanrt libuv)
+    add_dependencies(leanrt_initial-exec libuv)
+  endif()
 
   add_subdirectory(util)
   set(LEAN_OBJS ${LEAN_OBJS} $<TARGET_OBJECTS:util>)
@@ -562,7 +634,10 @@ if (${CMAKE_SYSTEM_NAME} MATCHES "Emscripten")
   # 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 " ${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")
+  # We set `ERROR_ON_UNDEFINED_SYMBOLS=0` because our build of LibUV does not
+  # define all symbols, see the comment about LibUV on WebAssembly further up
+  # in this file.
+  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 -s ERROR_ON_UNDEFINED_SYMBOLS=0")
 endif()
 
 # Build the compiler using the bootstrapped C sources for stage0, and use

src/Init.lean

@@ -35,3 +35,5 @@ import Init.Ext
 import Init.Omega
 import Init.MacroTrace
 import Init.Grind
+import Init.While
+import Init.Syntax

src/Init/Classical.lean

@@ -80,6 +80,8 @@ noncomputable scoped instance (priority := low) propDecidable (a : Prop) : Decid
 noncomputable def decidableInhabited (a : Prop) : Inhabited (Decidable a) where
   default := inferInstance
 
+instance (a : Prop) : Nonempty (Decidable a) := ⟨propDecidable a⟩
+
 noncomputable def typeDecidableEq (α : Sort u) : DecidableEq α :=
   fun _ _ => inferInstance
 

src/Init/Control/Basic.lean

@@ -8,6 +8,42 @@ import Init.Core
 
 universe u v w
 
+/--
+A `ForIn'` instance, which handles `for h : x in c do`,
+can also handle `for x in x do` by ignoring `h`, and so provides a `ForIn` instance.
+
+Note that this instance will cause a potentially non-defeq duplication if both `ForIn` and `ForIn'`
+instances are provided for the same type.
+-/
+-- We set the priority to 500 so it is below the default,
+-- but still above the low priority instance from `Stream`.
+instance (priority := 500) instForInOfForIn' [ForIn' m ρ α d] : ForIn m ρ α where
+  forIn x b f := forIn' x b fun a _ => f a
+
+@[simp] theorem forIn'_eq_forIn [d : Membership α ρ] [ForIn' m ρ α d] {β} [Monad m] (x : ρ) (b : β)
+    (f : (a : α) → a ∈ x → β → m (ForInStep β)) (g : (a : α) → β → m (ForInStep β))
+    (h : ∀ a m b, f a m b = g a b) :
+    forIn' x b f = forIn x b g := by
+  simp [instForInOfForIn']
+  congr
+  apply funext
+  intro a
+  apply funext
+  intro m
+  apply funext
+  intro b
+  simp [h]
+  rfl
+
+/-- Extract the value from a `ForInStep`, ignoring whether it is `done` or `yield`. -/
+def ForInStep.value (x : ForInStep α) : α :=
+  match x with
+  | ForInStep.done b => b
+  | ForInStep.yield b => b
+
+@[simp] theorem ForInStep.value_done (b : β) : (ForInStep.done b).value = b := rfl
+@[simp] theorem ForInStep.value_yield (b : β) : (ForInStep.yield b).value = b := rfl
+
 @[reducible]
 def Functor.mapRev {f : Type u → Type v} [Functor f] {α β : Type u} : f α → (α → β) → f β :=
   fun a f => f <$> a

src/Init/Control/Lawful/Basic.lean

@@ -33,6 +33,10 @@ attribute [simp] id_map
 @[simp] theorem id_map' [Functor m] [LawfulFunctor m] (x : m α) : (fun a => a) <$> x = x :=
   id_map x
 
+@[simp] theorem Functor.map_map [Functor f] [LawfulFunctor f] (m : α → β) (g : β → γ) (x : f α) :
+    g <$> m <$> x = (fun a => g (m a)) <$> x :=
+  (comp_map _ _ _).symm
+
 /--
 The `Applicative` typeclass only contains the operations of an applicative functor.
 `LawfulApplicative` further asserts that these operations satisfy the laws of an applicative functor:
@@ -83,12 +87,16 @@ class LawfulMonad (m : Type u → Type v) [Monad m] extends LawfulApplicative m
   seq_assoc x g h := (by simp [← bind_pure_comp, ← bind_map, bind_assoc, pure_bind])
 
 export LawfulMonad (bind_pure_comp bind_map pure_bind bind_assoc)
-attribute [simp] pure_bind bind_assoc
+attribute [simp] pure_bind bind_assoc bind_pure_comp
 
 @[simp] theorem bind_pure [Monad m] [LawfulMonad m] (x : m α) : x >>= pure = x := by
   show x >>= (fun a => pure (id a)) = x
   rw [bind_pure_comp, id_map]
 
+/--
+Use `simp [← bind_pure_comp]` rather than `simp [map_eq_pure_bind]`,
+as `bind_pure_comp` is in the default simp set, so also using `map_eq_pure_bind` would cause a loop.
+-/
 theorem map_eq_pure_bind [Monad m] [LawfulMonad m] (f : α → β) (x : m α) : f <$> x = x >>= fun a => pure (f a) := by
   rw [← bind_pure_comp]
 
@@ -109,10 +117,24 @@ theorem seq_eq_bind {α β : Type u} [Monad m] [LawfulMonad m] (mf : m (α →
 
 theorem seqRight_eq_bind [Monad m] [LawfulMonad m] (x : m α) (y : m β) : x *> y = x >>= fun _ => y := by
   rw [seqRight_eq]
-  simp [map_eq_pure_bind, seq_eq_bind_map, const]
+  simp only [map_eq_pure_bind, const, seq_eq_bind_map, bind_assoc, pure_bind, id_eq, bind_pure]
 
 theorem seqLeft_eq_bind [Monad m] [LawfulMonad m] (x : m α) (y : m β) : x <* y = x >>= fun a => y >>= fun _ => pure a := by
-  rw [seqLeft_eq]; simp [map_eq_pure_bind, seq_eq_bind_map]
+  rw [seqLeft_eq]
+  simp only [map_eq_pure_bind, seq_eq_bind_map, bind_assoc, pure_bind, const_apply]
+
+@[simp] theorem map_bind [Monad m] [LawfulMonad m] (f : β → γ) (x : m α) (g : α → m β) :
+    f <$> (x >>= g) = x >>= fun a => f <$> g a := by
+  rw [← bind_pure_comp, LawfulMonad.bind_assoc]
+  simp [bind_pure_comp]
+
+@[simp] theorem bind_map_left [Monad m] [LawfulMonad m] (f : α → β) (x : m α) (g : β → m γ) :
+    ((f <$> x) >>= fun b => g b) = (x >>= fun a => g (f a)) := by
+  rw [← bind_pure_comp]
+  simp only [bind_assoc, pure_bind]
+
+@[simp] theorem Functor.map_unit [Monad m] [LawfulMonad m] {a : m PUnit} : (fun _ => PUnit.unit) <$> a = a := by
+  simp [map]
 
 /--
 An alternative constructor for `LawfulMonad` which has more
@@ -161,9 +183,9 @@ end Id
 
 instance : LawfulMonad Option := LawfulMonad.mk'
   (id_map := fun x => by cases x <;> rfl)
-  (pure_bind := fun x f => rfl)
-  (bind_assoc := fun x f g => by cases x <;> rfl)
-  (bind_pure_comp := fun f x => by cases x <;> rfl)
+  (pure_bind := fun _ _ => rfl)
+  (bind_assoc := fun x _ _ => by cases x <;> rfl)
+  (bind_pure_comp := fun _ x => by cases x <;> rfl)
 
 instance : LawfulApplicative Option := inferInstance
 instance : LawfulFunctor Option := inferInstance

src/Init/Control/Lawful/Instances.lean

@@ -7,6 +7,7 @@ prelude
 import Init.Control.Lawful.Basic
 import Init.Control.Except
 import Init.Control.StateRef
+import Init.Ext
 
 open Function
 
@@ -14,7 +15,7 @@ open Function
 
 namespace ExceptT
 
-theorem ext {x y : ExceptT ε m α} (h : x.run = y.run) : x = y := by
+@[ext] theorem ext {x y : ExceptT ε m α} (h : x.run = y.run) : x = y := by
   simp [run] at h
   assumption
 
@@ -25,7 +26,7 @@ theorem ext {x y : ExceptT ε m α} (h : x.run = y.run) : x = y := by
 @[simp] theorem run_throw [Monad m] : run (throw e : ExceptT ε m β) = pure (Except.error e) := rfl
 
 @[simp] theorem run_bind_lift [Monad m] [LawfulMonad m] (x : m α) (f : α → ExceptT ε m β) : run (ExceptT.lift x >>= f : ExceptT ε m β) = x >>= fun a => run (f a) := by
-  simp[ExceptT.run, ExceptT.lift, bind, ExceptT.bind, ExceptT.mk, ExceptT.bindCont, map_eq_pure_bind]
+  simp [ExceptT.run, ExceptT.lift, bind, ExceptT.bind, ExceptT.mk, ExceptT.bindCont]
 
 @[simp] theorem bind_throw [Monad m] [LawfulMonad m] (f : α → ExceptT ε m β) : (throw e >>= f) = throw e := by
   simp [throw, throwThe, MonadExceptOf.throw, bind, ExceptT.bind, ExceptT.bindCont, ExceptT.mk]
@@ -43,7 +44,7 @@ theorem run_bind [Monad m] (x : ExceptT ε m α)
 
 @[simp] theorem run_map [Monad m] [LawfulMonad m] (f : α → β) (x : ExceptT ε m α)
     : (f <$> x).run = Except.map f <$> x.run := by
-  simp [Functor.map, ExceptT.map, map_eq_pure_bind]
+  simp [Functor.map, ExceptT.map, ←bind_pure_comp]
   apply bind_congr
   intro a; cases a <;> simp [Except.map]
 
@@ -62,7 +63,7 @@ protected theorem seqLeft_eq {α β ε : Type u} {m : Type u → Type v} [Monad
   intro
   | Except.error _ => simp
   | Except.ok _ =>
-    simp [map_eq_pure_bind]; apply bind_congr; intro b;
+    simp [←bind_pure_comp]; apply bind_congr; intro b;
     cases b <;> simp [comp, Except.map, const]
 
 protected theorem seqRight_eq [Monad m] [LawfulMonad m] (x : ExceptT ε m α) (y : ExceptT ε m β) : x *> y = const α id <$> x <*> y := by
@@ -84,14 +85,19 @@ instance [Monad m] [LawfulMonad m] : LawfulMonad (ExceptT ε m) where
   pure_bind      := by intros; apply ext; simp [run_bind]
   bind_assoc     := by intros; apply ext; simp [run_bind]; apply bind_congr; intro a; cases a <;> simp
 
+@[simp] theorem map_throw [Monad m] [LawfulMonad m] {α β : Type _} (f : α → β) (e : ε) :
+    f <$> (throw e : ExceptT ε m α) = (throw e : ExceptT ε m β) := by
+  simp only [ExceptT.instMonad, ExceptT.map, ExceptT.mk, throw, throwThe, MonadExceptOf.throw,
+    pure_bind]
+
 end ExceptT
 
 /-! # Except -/
 
 instance : LawfulMonad (Except ε) := LawfulMonad.mk'
   (id_map := fun x => by cases x <;> rfl)
-  (pure_bind := fun a f => rfl)
-  (bind_assoc := fun a f g => by cases a <;> rfl)
+  (pure_bind := fun _ _ => rfl)
+  (bind_assoc := fun a _ _ => by cases a <;> rfl)
 
 instance : LawfulApplicative (Except ε) := inferInstance
 instance : LawfulFunctor (Except ε) := inferInstance
@@ -100,7 +106,7 @@ instance : LawfulFunctor (Except ε) := inferInstance
 
 namespace ReaderT
 
-theorem ext {x y : ReaderT ρ m α} (h : ∀ ctx, x.run ctx = y.run ctx) : x = y := by
+@[ext] theorem ext {x y : ReaderT ρ m α} (h : ∀ ctx, x.run ctx = y.run ctx) : x = y := by
   simp [run] at h
   exact funext h
 
@@ -162,7 +168,7 @@ instance [Monad m] [LawfulMonad m] : LawfulMonad (StateRefT' ω σ m) :=
 
 namespace StateT
 
-theorem ext {x y : StateT σ m α} (h : ∀ s, x.run s = y.run s) : x = y :=
+@[ext] theorem ext {x y : StateT σ m α} (h : ∀ s, x.run s = y.run s) : x = y :=
   funext h
 
 @[simp] theorem run'_eq [Monad m] (x : StateT σ m α) (s : σ) : run' x s = (·.1) <$> run x s :=
@@ -175,7 +181,7 @@ theorem ext {x y : StateT σ m α} (h : ∀ s, x.run s = y.run s) : x = y :=
   simp [bind, StateT.bind, run]
 
 @[simp] theorem run_map {α β σ : Type u} [Monad m] [LawfulMonad m] (f : α → β) (x : StateT σ m α) (s : σ) : (f <$> x).run s = (fun (p : α × σ) => (f p.1, p.2)) <$> x.run s := by
-  simp [Functor.map, StateT.map, run, map_eq_pure_bind]
+  simp [Functor.map, StateT.map, run, ←bind_pure_comp]
 
 @[simp] theorem run_get [Monad m] (s : σ)    : (get : StateT σ m σ).run s = pure (s, s) := rfl
 
@@ -210,13 +216,13 @@ theorem run_bind_lift {α σ : Type u} [Monad m] [LawfulMonad m] (x : m α) (f :
 
 theorem seqRight_eq [Monad m] [LawfulMonad m] (x : StateT σ m α) (y : StateT σ m β) : x *> y = const α id <$> x <*> y := by
   apply ext; intro s
-  simp [map_eq_pure_bind, const]
+  simp [←bind_pure_comp, const]
   apply bind_congr; intro p; cases p
   simp [Prod.eta]
 
 theorem seqLeft_eq [Monad m] [LawfulMonad m] (x : StateT σ m α) (y : StateT σ m β) : x <* y = const β <$> x <*> y := by
   apply ext; intro s
-  simp [map_eq_pure_bind]
+  simp [←bind_pure_comp]
 
 instance [Monad m] [LawfulMonad m] : LawfulMonad (StateT σ m) where
   id_map         := by intros; apply ext; intros; simp[Prod.eta]
@@ -224,7 +230,7 @@ instance [Monad m] [LawfulMonad m] : LawfulMonad (StateT σ m) where
   seqLeft_eq     := seqLeft_eq
   seqRight_eq    := seqRight_eq
   pure_seq       := by intros; apply ext; intros; simp
-  bind_pure_comp := by intros; apply ext; intros; simp; apply LawfulMonad.bind_pure_comp
+  bind_pure_comp := by intros; apply ext; intros; simp
   bind_map       := by intros; rfl
   pure_bind      := by intros; apply ext; intros; simp
   bind_assoc     := by intros; apply ext; intros; simp

src/Init/Control/StateRef.lean

@@ -6,8 +6,7 @@ Authors: Leonardo de Moura, Sebastian Ullrich
 The State monad transformer using IO references.
 -/
 prelude
-import Init.System.IO
-import Init.Control.State
+import Init.System.ST
 
 def StateRefT' (ω : Type) (σ : Type) (m : Type → Type) (α : Type) : Type := ReaderT (ST.Ref ω σ) m α
 

src/Init/Conv.lean

@@ -7,6 +7,7 @@ Notation for operators defined at Prelude.lean
 -/
 prelude
 import Init.Tactics
+import Init.Meta
 
 namespace Lean.Parser.Tactic.Conv
 
@@ -46,12 +47,20 @@ scoped syntax (name := withAnnotateState)
 /-- `skip` does nothing. -/
 syntax (name := skip) "skip" : conv
 
-/-- Traverses into the left subterm of a binary operator.
-(In general, for an `n`-ary operator, it traverses into the second to last argument.) -/
+/--
+Traverses into the left subterm of a binary operator.
+
+In general, for an `n`-ary operator, it traverses into the second to last argument.
+It is a synonym for `arg -2`.
+-/
 syntax (name := lhs) "lhs" : conv
 
-/-- Traverses into the right subterm of a binary operator.
-(In general, for an `n`-ary operator, it traverses into the last argument.) -/
+/--
+Traverses into the right subterm of a binary operator.
+
+In general, for an `n`-ary operator, it traverses into the last argument.
+It is a synonym for `arg -1`.
+-/
 syntax (name := rhs) "rhs" : conv
 
 /-- Traverses into the function of a (unary) function application.
@@ -74,13 +83,17 @@ subgoals for all the function arguments. For example, if the target is `f x y` t
 `congr` produces two subgoals, one for `x` and one for `y`. -/
 syntax (name := congr) "congr" : conv
 
+syntax argArg := "@"? "-"? num
+
 /--
 * `arg i` traverses into the `i`'th argument of the target. For example if the
   target is `f a b c d` then `arg 1` traverses to `a` and `arg 3` traverses to `c`.
+  The index may be negative; `arg -1` traverses into the last argument,
+  `arg -2` into the second-to-last argument, and so on.
 * `arg @i` is the same as `arg i` but it counts all arguments instead of just the
   explicit arguments.
 * `arg 0` traverses into the function. If the target is `f a b c d`, `arg 0` traverses into `f`. -/
-syntax (name := arg) "arg " "@"? num : conv
+syntax (name := arg) "arg " argArg : conv
 
 /-- `ext x` traverses into a binder (a `fun x => e` or `∀ x, e` expression)
 to target `e`, introducing name `x` in the process. -/
@@ -130,11 +143,11 @@ For example, if we are searching for `f _` in `f (f a) = f b`:
 syntax (name := pattern) "pattern " (occs)? term : conv
 
 /-- `rw [thm]` rewrites the target using `thm`. See the `rw` tactic for more information. -/
-syntax (name := rewrite) "rewrite" (config)? rwRuleSeq : conv
+syntax (name := rewrite) "rewrite" optConfig rwRuleSeq : conv
 
 /-- `simp [thm]` performs simplification using `thm` and marked `@[simp]` lemmas.
 See the `simp` tactic for more information. -/
-syntax (name := simp) "simp" (config)? (discharger)? (&" only")?
+syntax (name := simp) "simp" optConfig (discharger)? (&" only")?
   (" [" withoutPosition((simpStar <|> simpErase <|> simpLemma),*) "]")? : conv
 
 /--
@@ -151,7 +164,7 @@ example (a : Nat): (0 + 0) = a - a := by
     rw [← Nat.sub_self a]
 ```
 -/
-syntax (name := dsimp) "dsimp" (config)? (discharger)? (&" only")?
+syntax (name := dsimp) "dsimp" optConfig (discharger)? (&" only")?
   (" [" withoutPosition((simpErase <|> simpLemma),*) "]")? : conv
 
 /-- `simp_match` simplifies match expressions. For example,
@@ -247,12 +260,12 @@ macro (name := failIfSuccess) tk:"fail_if_success " s:convSeq : conv =>
 
 /-- `rw [rules]` applies the given list of rewrite rules to the target.
 See the `rw` tactic for more information. -/
-macro "rw" c:(config)? s:rwRuleSeq : conv => `(conv| rewrite $[$c]? $s)
+macro "rw" c:optConfig s:rwRuleSeq : conv => `(conv| rewrite $c:optConfig $s)
 
-/-- `erw [rules]` is a shorthand for `rw (config := { transparency := .default }) [rules]`.
+/-- `erw [rules]` is a shorthand for `rw (transparency := .default) [rules]`.
 This does rewriting up to unfolding of regular definitions (by comparison to regular `rw`
 which only unfolds `@[reducible]` definitions). -/
-macro "erw" s:rwRuleSeq : conv => `(conv| rw (config := { transparency := .default }) $s)
+macro "erw" c:optConfig s:rwRuleSeq : conv => `(conv| rw $[$(getConfigItems c)]* (transparency := .default) $s:rwRuleSeq)
 
 /-- `args` traverses into all arguments. Synonym for `congr`. -/
 macro "args" : conv => `(conv| congr)
@@ -263,7 +276,7 @@ macro "right" : conv => `(conv| rhs)
 /-- `intro` traverses into binders. Synonym for `ext`. -/
 macro "intro" xs:(ppSpace colGt ident)* : conv => `(conv| ext $xs*)
 
-syntax enterArg := ident <|> ("@"? num)
+syntax enterArg := ident <|> argArg
 
 /-- `enter [arg, ...]` is a compact way to describe a path to a subterm.
 It is a shorthand for other conv tactics as follows:
@@ -272,12 +285,7 @@ It is a shorthand for other conv tactics as follows:
 * `enter [x]` (where `x` is an identifier) is equivalent to `ext x`.
 For example, given the target `f (g a (fun x => x b))`, `enter [1, 2, x, 1]`
 will traverse to the subterm `b`. -/
-syntax "enter" " [" withoutPosition(enterArg,+) "]" : conv
-macro_rules
-  | `(conv| enter [$i:num]) => `(conv| arg $i)
-  | `(conv| enter [@$i]) => `(conv| arg @$i)
-  | `(conv| enter [$id:ident]) => `(conv| ext $id)
-  | `(conv| enter [$arg, $args,*]) => `(conv| (enter [$arg]; enter [$args,*]))
+syntax (name := enter) "enter" " [" withoutPosition(enterArg,+) "]" : conv
 
 /-- The `apply thm` conv tactic is the same as `apply thm` the tactic.
 There are no restrictions on `thm`, but strange results may occur if `thm`

src/Init/Core.lean

@@ -324,7 +324,6 @@ class ForIn' (m : Type u₁ → Type u₂) (ρ : Type u) (α : outParam (Type v)
 
 export ForIn' (forIn')
 
-
 /--
 Auxiliary type used to compile `do` notation. It is used when compiling a do block
 nested inside a combinator like `tryCatch`. It encodes the possible ways the
@@ -823,6 +822,7 @@ theorem iff_iff_implies_and_implies {a b : Prop} : (a ↔ b) ↔ (a → b) ∧ (
 protected theorem Iff.rfl {a : Prop} : a ↔ a :=
   Iff.refl a
 
+-- And, also for backward compatibility, we try `Iff.rfl.` using `exact` (see #5366)
 macro_rules | `(tactic| rfl) => `(tactic| exact Iff.rfl)
 
 theorem Iff.of_eq (h : a = b) : a ↔ b := h ▸ Iff.rfl
@@ -837,6 +837,9 @@ 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 HEq.comm {a : α} {b : β} : HEq a b ↔ HEq b a := Iff.intro HEq.symm HEq.symm
+theorem heq_comm {a : α} {b : β} : HEq a b ↔ HEq b a := HEq.comm
+
 @[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
@@ -858,16 +861,21 @@ theorem Exists.elim {α : Sort u} {p : α → Prop} {b : Prop}
 
 /-! # Decidable -/
 
-theorem decide_true_eq_true (h : Decidable True) : @decide True h = true :=
+@[simp] theorem decide_true (h : Decidable True) : @decide True h = true :=
   match h with
   | isTrue _  => rfl
   | isFalse h => False.elim <| h ⟨⟩
 
-theorem decide_false_eq_false (h : Decidable False) : @decide False h = false :=
+@[simp] theorem decide_false (h : Decidable False) : @decide False h = false :=
   match h with
   | isFalse _ => rfl
   | isTrue h  => False.elim h
 
+set_option linter.missingDocs false in
+@[deprecated decide_true (since := "2024-11-05")] abbrev decide_true_eq_true := decide_true
+set_option linter.missingDocs false in
+@[deprecated decide_false (since := "2024-11-05")] abbrev decide_false_eq_false := decide_false
+
 /-- Similar to `decide`, but uses an explicit instance -/
 @[inline] def toBoolUsing {p : Prop} (d : Decidable p) : Bool :=
   decide (h := d)
@@ -1381,6 +1389,7 @@ gen_injective_theorems% Except
 gen_injective_theorems% EStateM.Result
 gen_injective_theorems% Lean.Name
 gen_injective_theorems% Lean.Syntax
+gen_injective_theorems% BitVec
 
 theorem Nat.succ.inj {m n : Nat} : m.succ = n.succ → m = n :=
   fun x => Nat.noConfusion x id
@@ -1860,7 +1869,8 @@ section
 variable {α : Type u}
 variable (r : α → α → Prop)
 
-instance {α : Sort u} {s : Setoid α} [d : ∀ (a b : α), Decidable (a ≈ b)] : DecidableEq (Quotient s) :=
+instance Quotient.decidableEq {α : Sort u} {s : Setoid α} [d : ∀ (a b : α), Decidable (a ≈ b)]
+    : DecidableEq (Quotient s) :=
   fun (q₁ q₂ : Quotient s) =>
     Quotient.recOnSubsingleton₂ q₁ q₂
       fun a₁ a₂ =>
@@ -1931,15 +1941,6 @@ instance : Subsingleton (Squash α) where
     apply Quot.sound
     trivial
 
-/-! # Relations -/
-
-/--
-`Antisymm (·≤·)` says that `(·≤·)` is antisymmetric, that is, `a ≤ b → b ≤ a → a = b`.
--/
-class Antisymm {α : Sort u} (r : α → α → Prop) : Prop where
-  /-- An antisymmetric relation `(·≤·)` satisfies `a ≤ b → b ≤ a → a = b`. -/
-  antisymm {a b : α} : r a b → r b a → a = b
-
 namespace Lean
 /-! # Kernel reduction hints -/
 
@@ -2115,4 +2116,14 @@ instance : Commutative Or := ⟨fun _ _ => propext or_comm⟩
 instance : Commutative And := ⟨fun _ _ => propext and_comm⟩
 instance : Commutative Iff := ⟨fun _ _ => propext iff_comm⟩
 
+/--
+`Antisymm (·≤·)` says that `(·≤·)` is antisymmetric, that is, `a ≤ b → b ≤ a → a = b`.
+-/
+class Antisymm (r : α → α → Prop) : Prop where
+  /-- An antisymmetric relation `(·≤·)` satisfies `a ≤ b → b ≤ a → a = b`. -/
+  antisymm {a b : α} : r a b → r b a → a = b
+
+@[deprecated Antisymm (since := "2024-10-16"), inherit_doc Antisymm]
+abbrev _root_.Antisymm (r : α → α → Prop) : Prop := Std.Antisymm r
+
 end Std

src/Init/Data.lean

@@ -19,6 +19,7 @@ import Init.Data.ByteArray
 import Init.Data.FloatArray
 import Init.Data.Fin
 import Init.Data.UInt
+import Init.Data.SInt
 import Init.Data.Float
 import Init.Data.Option
 import Init.Data.Ord
@@ -40,3 +41,4 @@ import Init.Data.ULift
 import Init.Data.PLift
 import Init.Data.Zero
 import Init.Data.NeZero
+import Init.Data.Function

src/Init/Data/Array.lean

@@ -16,3 +16,5 @@ import Init.Data.Array.Lemmas
 import Init.Data.Array.TakeDrop
 import Init.Data.Array.Bootstrap
 import Init.Data.Array.GetLit
+import Init.Data.Array.MapIdx
+import Init.Data.Array.Set

src/Init/Data/Array/Attach.lean

@@ -5,6 +5,7 @@ Authors: Joachim Breitner, Mario Carneiro
 -/
 prelude
 import Init.Data.Array.Mem
+import Init.Data.Array.Lemmas
 import Init.Data.List.Attach
 
 namespace Array
@@ -26,4 +27,152 @@ Unsafe implementation of `attachWith`, taking advantage of the fact that the rep
   with the same elements but in the type `{x // x ∈ xs}`. -/
 @[inline] def attach (xs : Array α) : Array {x // x ∈ xs} := xs.attachWith _ fun _ => id
 
+@[simp] theorem _root_.List.attachWith_toArray {l : List α} {P : α → Prop} {H : ∀ x ∈ l.toArray, P x} :
+    l.toArray.attachWith P H = (l.attachWith P (by simpa using H)).toArray := by
+  simp [attachWith]
+
+@[simp] theorem _root_.List.attach_toArray {l : List α} :
+    l.toArray.attach = (l.attachWith (· ∈ l.toArray) (by simp)).toArray := by
+  simp [attach]
+
+@[simp] theorem toList_attachWith {l : Array α} {P : α → Prop} {H : ∀ x ∈ l, P x} :
+   (l.attachWith P H).toList = l.toList.attachWith P (by simpa [mem_toList] using H) := by
+  simp [attachWith]
+
+@[simp] theorem toList_attach {α : Type _} {l : Array α} :
+    l.attach.toList = l.toList.attachWith (· ∈ l) (by simp [mem_toList]) := by
+  simp [attach]
+
+/-! ## unattach
+
+`Array.unattach` is the (one-sided) inverse of `Array.attach`. It is a synonym for `Array.map Subtype.val`.
+
+We use it by providing a simp lemma `l.attach.unattach = l`, and simp lemmas which recognize higher order
+functions applied to `l : Array { x // p x }` which only depend on the value, not the predicate, and rewrite these
+in terms of a simpler function applied to `l.unattach`.
+
+Further, we provide simp lemmas that push `unattach` inwards.
+-/
+
+/--
+A synonym for `l.map (·.val)`. Mostly this should not be needed by users.
+It is introduced as in intermediate step by lemmas such as `map_subtype`,
+and is ideally subsequently simplified away by `unattach_attach`.
+
+If not, usually the right approach is `simp [Array.unattach, -Array.map_subtype]` to unfold.
+-/
+def unattach {α : Type _} {p : α → Prop} (l : Array { x // p x }) := l.map (·.val)
+
+@[simp] theorem unattach_nil {p : α → Prop} : (#[] : Array { x // p x }).unattach = #[] := rfl
+@[simp] theorem unattach_push {p : α → Prop} {a : { x // p x }} {l : Array { x // p x }} :
+    (l.push a).unattach = l.unattach.push a.1 := by
+  simp only [unattach, Array.map_push]
+
+@[simp] theorem size_unattach {p : α → Prop} {l : Array { x // p x }} :
+    l.unattach.size = l.size := by
+  unfold unattach
+  simp
+
+@[simp] theorem _root_.List.unattach_toArray {p : α → Prop} {l : List { x // p x }} :
+    l.toArray.unattach = l.unattach.toArray := by
+  simp only [unattach, List.map_toArray, List.unattach]
+
+@[simp] theorem toList_unattach {p : α → Prop} {l : Array { x // p x }} :
+    l.unattach.toList = l.toList.unattach := by
+  simp only [unattach, toList_map, List.unattach]
+
+@[simp] theorem unattach_attach {l : Array α} : l.attach.unattach = l := by
+  cases l
+  simp
+
+@[simp] theorem unattach_attachWith {p : α → Prop} {l : Array α}
+    {H : ∀ a ∈ l, p a} :
+    (l.attachWith p H).unattach = l := by
+  cases l
+  simp
+
+/-! ### Recognizing higher order functions using a function that only depends on the value. -/
+
+/--
+This lemma identifies folds over arrays of subtypes, where the function only depends on the value, not the proposition,
+and simplifies these to the function directly taking the value.
+-/
+theorem foldl_subtype {p : α → Prop} {l : Array { x // p x }}
+    {f : β → { x // p x } → β} {g : β → α → β} {x : β}
+    {hf : ∀ b x h, f b ⟨x, h⟩ = g b x} :
+    l.foldl f x = l.unattach.foldl g x := by
+  cases l
+  simp only [List.foldl_toArray', List.unattach_toArray]
+  rw [List.foldl_subtype] -- Why can't simp do this?
+  simp [hf]
+
+/-- Variant of `foldl_subtype` with side condition to check `stop = l.size`. -/
+@[simp] theorem foldl_subtype' {p : α → Prop} {l : Array { x // p x }}
+    {f : β → { x // p x } → β} {g : β → α → β} {x : β}
+    {hf : ∀ b x h, f b ⟨x, h⟩ = g b x} (h : stop = l.size) :
+    l.foldl f x 0 stop = l.unattach.foldl g x := by
+  subst h
+  rwa [foldl_subtype]
+
+/--
+This lemma identifies folds over arrays of subtypes, where the function only depends on the value, not the proposition,
+and simplifies these to the function directly taking the value.
+-/
+theorem foldr_subtype {p : α → Prop} {l : Array { x // p x }}
+    {f : { x // p x } → β → β} {g : α → β → β} {x : β}
+    {hf : ∀ x h b, f ⟨x, h⟩ b = g x b} :
+    l.foldr f x = l.unattach.foldr g x := by
+  cases l
+  simp only [List.foldr_toArray', List.unattach_toArray]
+  rw [List.foldr_subtype]
+  simp [hf]
+
+/-- Variant of `foldr_subtype` with side condition to check `stop = l.size`. -/
+@[simp] theorem foldr_subtype' {p : α → Prop} {l : Array { x // p x }}
+    {f : { x // p x } → β → β} {g : α → β → β} {x : β}
+    {hf : ∀ x h b, f ⟨x, h⟩ b = g x b} (h : start = l.size) :
+    l.foldr f x start 0 = l.unattach.foldr g x := by
+  subst h
+  rwa [foldr_subtype]
+
+/--
+This lemma identifies maps over arrays of subtypes, where the function only depends on the value, not the proposition,
+and simplifies these to the function directly taking the value.
+-/
+@[simp] theorem map_subtype {p : α → Prop} {l : Array { x // p x }}
+    {f : { x // p x } → β} {g : α → β} {hf : ∀ x h, f ⟨x, h⟩ = g x} :
+    l.map f = l.unattach.map g := by
+  cases l
+  simp only [List.map_toArray, List.unattach_toArray]
+  rw [List.map_subtype]
+  simp [hf]
+
+@[simp] theorem filterMap_subtype {p : α → Prop} {l : Array { x // p x }}
+    {f : { x // p x } → Option β} {g : α → Option β} {hf : ∀ x h, f ⟨x, h⟩ = g x} :
+    l.filterMap f = l.unattach.filterMap g := by
+  cases l
+  simp only [size_toArray, List.filterMap_toArray', List.unattach_toArray, List.length_unattach,
+    mk.injEq]
+  rw [List.filterMap_subtype]
+  simp [hf]
+
+@[simp] theorem unattach_filter {p : α → Prop} {l : Array { x // p x }}
+    {f : { x // p x } → Bool} {g : α → Bool} {hf : ∀ x h, f ⟨x, h⟩ = g x} :
+    (l.filter f).unattach = l.unattach.filter g := by
+  cases l
+  simp [hf]
+
+/-! ### Simp lemmas pushing `unattach` inwards. -/
+
+@[simp] theorem unattach_reverse {p : α → Prop} {l : Array { x // p x }} :
+    l.reverse.unattach = l.unattach.reverse := by
+  cases l
+  simp
+
+@[simp] theorem unattach_append {p : α → Prop} {l₁ l₂ : Array { x // p x }} :
+    (l₁ ++ l₂).unattach = l₁.unattach ++ l₂.unattach := by
+  cases l₁
+  cases l₂
+  simp
+
 end Array

src/Init/Data/Array/Basic.lean

@@ -7,10 +7,12 @@ prelude
 import Init.WFTactics
 import Init.Data.Nat.Basic
 import Init.Data.Fin.Basic
-import Init.Data.UInt.Basic
+import Init.Data.UInt.BasicAux
 import Init.Data.Repr
 import Init.Data.ToString.Basic
 import Init.GetElem
+import Init.Data.List.ToArray
+import Init.Data.Array.Set
 universe u v w
 
 /-! ### Array literal syntax -/
@@ -24,9 +26,12 @@ variable {α : Type u}
 
 namespace Array
 
+@[deprecated toList (since := "2024-10-13")] abbrev data := @toList
+
 /-! ### Preliminary theorems -/
 
-@[simp] theorem size_set (a : Array α) (i : Fin a.size) (v : α) : (set a i v).size = a.size :=
+@[simp] theorem size_set (a : Array α) (i : Nat) (v : α) (h : i < a.size) :
+    (set a i v h).size = a.size :=
   List.length_set ..
 
 @[simp] theorem size_push (a : Array α) (v : α) : (push a v).size = a.size + 1 :=
@@ -77,6 +82,42 @@ theorem ext' {as bs : Array α} (h : as.toList = bs.toList) : as = bs := by
 
 @[simp] theorem size_toArray (as : List α) : as.toArray.size = as.length := by simp [size]
 
+@[simp] theorem getElem_toList {a : Array α} {i : Nat} (h : i < a.size) : a.toList[i] = a[i] := rfl
+
+/-- `a ∈ as` is a predicate which asserts that `a` is in the array `as`. -/
+-- NB: This is defined as a structure rather than a plain def so that a lemma
+-- like `sizeOf_lt_of_mem` will not apply with no actual arrays around.
+structure Mem (as : Array α) (a : α) : Prop where
+  val : a ∈ as.toList
+
+instance : Membership α (Array α) where
+  mem := Mem
+
+theorem mem_def {a : α} {as : Array α} : a ∈ as ↔ a ∈ as.toList :=
+  ⟨fun | .mk h => h, Array.Mem.mk⟩
+
+@[simp] theorem getElem_mem {l : Array α} {i : Nat} (h : i < l.size) : l[i] ∈ l := by
+  rw [Array.mem_def, ← getElem_toList]
+  apply List.getElem_mem
+
+end Array
+
+namespace List
+
+@[simp] theorem toArray_toList (a : Array α) : a.toList.toArray = a := rfl
+
+@[simp] theorem getElem_toArray {a : List α} {i : Nat} (h : i < a.toArray.size) :
+    a.toArray[i] = a[i]'(by simpa using h) := rfl
+
+@[simp] theorem getElem?_toArray {a : List α} {i : Nat} : a.toArray[i]? = a[i]? := rfl
+
+@[simp] theorem getElem!_toArray [Inhabited α] {a : List α} {i : Nat} :
+    a.toArray[i]! = a[i]! := rfl
+
+end List
+
+namespace Array
+
 @[deprecated toList_toArray (since := "2024-09-09")] abbrev data_toArray := @toList_toArray
 
 @[deprecated Array.toList (since := "2024-09-10")] abbrev Array.data := @Array.toList
@@ -102,7 +143,7 @@ def uget (a : @& Array α) (i : USize) (h : i.toNat < a.size) : α :=
    `fset` may be slightly slower than `uset`. -/
 @[extern "lean_array_uset"]
 def uset (a : Array α) (i : USize) (v : α) (h : i.toNat < a.size) : Array α :=
-  a.set ⟨i.toNat, h⟩ v
+  a.set i.toNat v h
 
 @[extern "lean_array_pop"]
 def pop (a : Array α) : Array α where
@@ -125,13 +166,14 @@ count of 1 when called.
 -/
 @[extern "lean_array_fswap"]
 def swap (a : Array α) (i j : @& Fin a.size) : Array α :=
-  let v₁ := a.get i
-  let v₂ := a.get j
+  let v₁ := a[i]
+  let v₂ := a[j]
   let a'  := a.set i v₂
-  a'.set (size_set a i v₂ ▸ j) v₁
+  a'.set j v₁ (Nat.lt_of_lt_of_eq j.isLt (size_set a i v₂ _).symm)
 
 @[simp] theorem size_swap (a : Array α) (i j : Fin a.size) : (a.swap i j).size = a.size := by
-  show ((a.set i (a.get j)).set (size_set a i _ ▸ j) (a.get i)).size = a.size
+  show ((a.set i a[j]).set j a[i]
+    (Nat.lt_of_lt_of_eq j.isLt (size_set a i a[j] _).symm)).size = a.size
   rw [size_set, size_set]
 
 /--
@@ -196,17 +238,19 @@ def range (n : Nat) : Array Nat :=
 def singleton (v : α) : Array α :=
   mkArray 1 v
 
-def back [Inhabited α] (a : Array α) : α :=
+def back! [Inhabited α] (a : Array α) : α :=
   a.get! (a.size - 1)
 
+@[deprecated back! (since := "2024-10-31")] abbrev back := @back!
+
 def get? (a : Array α) (i : Nat) : Option α :=
   if h : i < a.size then some a[i] else none
 
 def back? (a : Array α) : Option α :=
-  a.get? (a.size - 1)
+  a[a.size - 1]?
 
 @[inline] def swapAt (a : Array α) (i : Fin a.size) (v : α) : α × Array α :=
-  let e := a.get i
+  let e := a[i]
   let a := a.set i v
   (e, a)
 
@@ -215,36 +259,37 @@ def swapAt! (a : Array α) (i : Nat) (v : α) : α × Array α :=
   if h : i < a.size then
     swapAt a ⟨i, h⟩ v
   else
-    have : Inhabited α := ⟨v⟩
+    have : Inhabited (α × Array α) := ⟨(v, a)⟩
     panic! ("index " ++ toString i ++ " out of bounds")
 
-def shrink (a : Array α) (n : Nat) : Array α :=
+/-- `take a n` returns the first `n` elements of `a`. -/
+def take (a : Array α) (n : Nat) : Array α :=
   let rec loop
     | 0,   a => a
     | n+1, a => loop n a.pop
   loop (a.size - n) a
 
+@[deprecated take (since := "2024-10-22")] abbrev shrink := @take
+
 @[inline]
 unsafe def modifyMUnsafe [Monad m] (a : Array α) (i : Nat) (f : α → m α) : m (Array α) := do
   if h : i < a.size then
-    let idx : Fin a.size := ⟨i, h⟩
-    let v                := a.get idx
+    let v                := a[i]
     -- Replace a[i] by `box(0)`.  This ensures that `v` remains unshared if possible.
     -- Note: we assume that arrays have a uniform representation irrespective
     -- of the element type, and that it is valid to store `box(0)` in any array.
-    let a'               := a.set idx (unsafeCast ())
+    let a'               := a.set i (unsafeCast ())
     let v ← f v
-    pure <| a'.set (size_set a .. ▸ idx) v
+    pure <| a'.set i v (Nat.lt_of_lt_of_eq h (size_set a ..).symm)
   else
     pure a
 
 @[implemented_by modifyMUnsafe]
 def modifyM [Monad m] (a : Array α) (i : Nat) (f : α → m α) : m (Array α) := do
   if h : i < a.size then
-    let idx := ⟨i, h⟩
-    let v   := a.get idx
+    let v   := a[i]
     let v ← f v
-    pure <| a.set idx v
+    pure <| a.set i v
   else
     pure a
 
@@ -260,21 +305,21 @@ def modifyOp (self : Array α) (idx : Nat) (f : α → α) : Array α :=
   We claim this unsafe implementation is correct because an array cannot have more than `usizeSz` elements in our runtime.
 
   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 :=
+@[inline] unsafe def forIn'Unsafe {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m] (as : Array α) (b : β) (f : (a : α) → a ∈ as → β → m (ForInStep β)) : m β :=
   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
-      match (← f a b) with
+      match (← f a lcProof b) with
       | ForInStep.done  b => pure b
       | ForInStep.yield b => loop (i+1) b
     else
       pure b
   loop 0 b
 
-/-- Reference implementation for `forIn` -/
-@[implemented_by Array.forInUnsafe]
-protected def forIn {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 :=
+/-- Reference implementation for `forIn'` -/
+@[implemented_by Array.forIn'Unsafe]
+protected def forIn' {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m] (as : Array α) (b : β) (f : (a : α) → a ∈ as → β → m (ForInStep β)) : m β :=
   let rec loop (i : Nat) (h : i ≤ as.size) (b : β) : m β := do
     match i, h with
     | 0,   _ => pure b
@@ -282,15 +327,17 @@ protected def forIn {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m
       have h' : i < as.size            := Nat.lt_of_lt_of_le (Nat.lt_succ_self i) h
       have : as.size - 1 < as.size     := Nat.sub_lt (Nat.zero_lt_of_lt h') (by decide)
       have : as.size - 1 - i < as.size := Nat.lt_of_le_of_lt (Nat.sub_le (as.size - 1) i) this
-      match (← f as[as.size - 1 - i] b) with
+      match (← f as[as.size - 1 - i] (getElem_mem this) b) with
       | ForInStep.done b  => pure b
       | ForInStep.yield b => loop i (Nat.le_of_lt h') b
   loop as.size (Nat.le_refl _) b
 
-instance : ForIn m (Array α) α where
-  forIn := Array.forIn
+instance : ForIn' m (Array α) α inferInstance where
+  forIn' := Array.forIn'
 
-/-- See comment at `forInUnsafe` -/
+-- No separate `ForIn` instance is required because it can be derived from `ForIn'`.
+
+/-- See comment at `forIn'Unsafe` -/
 @[inline]
 unsafe def foldlMUnsafe {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m] (f : β → α → m β) (init : β) (as : Array α) (start := 0) (stop := as.size) : m β :=
   let rec @[specialize] fold (i : USize) (stop : USize) (b : β) : m β := do
@@ -325,7 +372,7 @@ def foldlM {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m] (f : β
   else
     fold as.size (Nat.le_refl _)
 
-/-- See comment at `forInUnsafe` -/
+/-- See comment at `forIn'Unsafe` -/
 @[inline]
 unsafe def foldrMUnsafe {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m] (f : α → β → m β) (init : β) (as : Array α) (start := as.size) (stop := 0) : m β :=
   let rec @[specialize] fold (i : USize) (stop : USize) (b : β) : m β := do
@@ -364,7 +411,7 @@ def foldrM {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m] (f : α
   else
     pure init
 
-/-- See comment at `forInUnsafe` -/
+/-- See comment at `forIn'Unsafe` -/
 @[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 := as.usize
@@ -395,22 +442,29 @@ def mapM {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m] (f : α
   decreasing_by simp_wf; decreasing_trivial_pre_omega
   map 0 (mkEmpty as.size)
 
+@[deprecated mapM (since := "2024-11-11")] abbrev sequenceMap := @mapM
+
+/-- Variant of `mapIdxM` which receives the index as a `Fin as.size`. -/
 @[inline]
-def mapIdxM {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m] (as : Array α) (f : Fin as.size → α → m β) : m (Array β) :=
+def mapFinIdxM {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m]
+    (as : Array α) (f : Fin as.size → α → m β) : m (Array β) :=
   let rec @[specialize] map (i : Nat) (j : Nat) (inv : i + j = as.size) (bs : Array β) : m (Array β) := do
     match i, inv with
     | 0,    _  => pure bs
     | i+1, inv =>
-      have : j < as.size := by
+      have j_lt : j < as.size := by
         rw [← inv, Nat.add_assoc, Nat.add_comm 1 j, Nat.add_comm]
         apply Nat.le_add_right
-      let idx : Fin as.size := ⟨j, this⟩
       have : i + (j + 1) = as.size := by rw [← inv, Nat.add_comm j 1, Nat.add_assoc]
-      map i (j+1) this (bs.push (← f idx (as.get idx)))
+      map i (j+1) this (bs.push (← f ⟨j, j_lt⟩ (as.get j j_lt)))
   map as.size 0 rfl (mkEmpty as.size)
 
 @[inline]
-def findSomeM? {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m] (as : Array α) (f : α → m (Option β)) : m (Option β) := do
+def mapIdxM {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m] (f : Nat → α → m β) (as : Array α) : m (Array β) :=
+  as.mapFinIdxM fun i a => f i a
+
+@[inline]
+def findSomeM? {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m] (f : α → m (Option β)) (as : Array α) : m (Option β) := do
   for a in as do
     match (← f a) with
     | some b => return b
@@ -418,14 +472,14 @@ def findSomeM? {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m] (as
   return none
 
 @[inline]
-def findM? {α : Type} {m : Type → Type} [Monad m] (as : Array α) (p : α → m Bool) : m (Option α) := do
+def findM? {α : Type} {m : Type → Type} [Monad m] (p : α → m Bool) (as : Array α) : m (Option α) := do
   for a in as do
     if (← p a) then
       return a
   return none
 
 @[inline]
-def findIdxM? [Monad m] (as : Array α) (p : α → m Bool) : m (Option Nat) := do
+def findIdxM? [Monad m] (p : α → m Bool) (as : Array α) : m (Option Nat) := do
   let mut i := 0
   for a in as do
     if (← p a) then
@@ -477,7 +531,7 @@ def allM {α : Type u} {m : Type → Type w} [Monad m] (p : α → m Bool) (as :
   return !(← as.anyM (start := start) (stop := stop) fun v => return !(← p v))
 
 @[inline]
-def findSomeRevM? {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m] (as : Array α) (f : α → m (Option β)) : m (Option β) :=
+def findSomeRevM? {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m] (f : α → m (Option β)) (as : Array α) : m (Option β) :=
   let rec @[specialize] find : (i : Nat) → i ≤ as.size → m (Option β)
     | 0,   _ => pure none
     | i+1, h => do
@@ -491,7 +545,7 @@ def findSomeRevM? {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m]
   find as.size (Nat.le_refl _)
 
 @[inline]
-def findRevM? {α : Type} {m : Type → Type w} [Monad m] (as : Array α) (p : α → m Bool) : m (Option α) :=
+def findRevM? {α : Type} {m : Type → Type w} [Monad m] (p : α → m Bool) (as : Array α) : m (Option α) :=
   as.findSomeRevM? fun a => return if (← p a) then some a else none
 
 @[inline]
@@ -514,8 +568,13 @@ def foldr {α : Type u} {β : Type v} (f : α → β → β) (init : β) (as : A
 def map {α : Type u} {β : Type v} (f : α → β) (as : Array α) : Array β :=
   Id.run <| as.mapM f
 
+/-- Variant of `mapIdx` which receives the index as a `Fin as.size`. -/
 @[inline]
-def mapIdx {α : Type u} {β : Type v} (as : Array α) (f : Fin as.size → α → β) : Array β :=
+def mapFinIdx {α : Type u} {β : Type v} (as : Array α) (f : Fin as.size → α → β) : Array β :=
+  Id.run <| as.mapFinIdxM f
+
+@[inline]
+def mapIdx {α : Type u} {β : Type v} (f : Nat → α → β) (as : Array α) : Array β :=
   Id.run <| as.mapIdxM f
 
 /-- Turns `#[a, b]` into `#[(a, 0), (b, 1)]`. -/
@@ -523,29 +582,29 @@ def zipWithIndex (arr : Array α) : Array (α × Nat) :=
   arr.mapIdx fun i a => (a, i)
 
 @[inline]
-def find? {α : Type} (as : Array α) (p : α → Bool) : Option α :=
+def find? {α : Type} (p : α → Bool) (as : Array α) : Option α :=
   Id.run <| as.findM? p
 
 @[inline]
-def findSome? {α : Type u} {β : Type v} (as : Array α) (f : α → Option β) : Option β :=
+def findSome? {α : Type u} {β : Type v} (f : α → Option β) (as : Array α) : Option β :=
   Id.run <| as.findSomeM? f
 
 @[inline]
-def findSome! {α : Type u} {β : Type v} [Inhabited β] (a : Array α) (f : α → Option β) : β :=
-  match findSome? a f with
+def findSome! {α : Type u} {β : Type v} [Inhabited β] (f : α → Option β) (a : Array α) : β :=
+  match a.findSome? f with
   | some b => b
   | none   => panic! "failed to find element"
 
 @[inline]
-def findSomeRev? {α : Type u} {β : Type v} (as : Array α) (f : α → Option β) : Option β :=
+def findSomeRev? {α : Type u} {β : Type v} (f : α → Option β) (as : Array α) : Option β :=
   Id.run <| as.findSomeRevM? f
 
 @[inline]
-def findRev? {α : Type} (as : Array α) (p : α → Bool) : Option α :=
+def findRev? {α : Type} (p : α → Bool) (as : Array α) : Option α :=
   Id.run <| as.findRevM? p
 
 @[inline]
-def findIdx? {α : Type u} (as : Array α) (p : α → Bool) : Option Nat :=
+def findIdx? {α : Type u} (p : α → Bool) (as : Array α) : Option Nat :=
   let rec @[semireducible] -- This is otherwise irreducible because it uses well-founded recursion.
   loop (j : Nat) :=
     if h : j < as.size then
@@ -560,8 +619,7 @@ def getIdx? [BEq α] (a : Array α) (v : α) : Option Nat :=
 @[semireducible] -- This is otherwise irreducible because it uses well-founded recursion.
 def indexOfAux [BEq α] (a : Array α) (v : α) (i : Nat) : Option (Fin a.size) :=
   if h : i < a.size then
-    let idx : Fin a.size := ⟨i, h⟩;
-    if a.get idx == v then some idx
+    if a[i] == v then some ⟨i, h⟩
     else indexOfAux a v (i+1)
   else none
 decreasing_by simp_wf; decreasing_trivial_pre_omega
@@ -606,18 +664,22 @@ protected def appendList (as : Array α) (bs : List α) : Array α :=
 instance : HAppend (Array α) (List α) (Array α) := ⟨Array.appendList⟩
 
 @[inline]
-def concatMapM [Monad m] (f : α → m (Array β)) (as : Array α) : m (Array β) :=
+def flatMapM [Monad m] (f : α → m (Array β)) (as : Array α) : m (Array β) :=
   as.foldlM (init := empty) fun bs a => do return bs ++ (← f a)
 
+@[deprecated flatMapM (since := "2024-10-16")] abbrev concatMapM := @flatMapM
+
 @[inline]
-def concatMap (f : α → Array β) (as : Array α) : Array β :=
+def flatMap (f : α → Array β) (as : Array α) : Array β :=
   as.foldl (init := empty) fun bs a => bs ++ f a
 
+@[deprecated flatMap (since := "2024-10-16")] abbrev concatMap := @flatMap
+
 /-- Joins array of array into a single array.
 
 `flatten #[#[a₁, a₂, ⋯], #[b₁, b₂, ⋯], ⋯]` = `#[a₁, a₂, ⋯, b₁, b₂, ⋯]`
 -/
-def flatten (as : Array (Array α)) : Array α :=
+@[inline] def flatten (as : Array (Array α)) : Array α :=
   as.foldl (init := empty) fun r a => r ++ a
 
 @[inline]
@@ -682,7 +744,7 @@ where
 @[semireducible] -- This is otherwise irreducible because it uses well-founded recursion.
 def popWhile (p : α → Bool) (as : Array α) : Array α :=
   if h : as.size > 0 then
-    if p (as.get ⟨as.size - 1, Nat.sub_lt h (by decide)⟩) then
+    if p (as[as.size - 1]'(Nat.sub_lt h (by decide))) then
       popWhile p as.pop
     else
       as
@@ -694,7 +756,7 @@ def takeWhile (p : α → Bool) (as : Array α) : Array α :=
   let rec @[semireducible] -- This is otherwise irreducible because it uses well-founded recursion.
   go (i : Nat) (r : Array α) : Array α :=
     if h : i < as.size then
-      let a := as.get ⟨i, h⟩
+      let a := as[i]
       if p a then
         go (i+1) (r.push a)
       else
@@ -720,7 +782,7 @@ termination_by a.size - i.val
 decreasing_by simp_wf; exact Nat.sub_succ_lt_self _ _ i.isLt
 
 -- This is required in `Lean.Data.PersistentHashMap`.
-theorem size_feraseIdx (a : Array α) (i : Fin a.size) : (a.feraseIdx i).size = a.size - 1 := by
+@[simp] theorem size_feraseIdx (a : Array α) (i : Fin a.size) : (a.feraseIdx i).size = a.size - 1 := by
   induction a, i using Array.feraseIdx.induct with
   | @case1 a i h a' _ ih =>
     unfold feraseIdx
@@ -806,15 +868,38 @@ def zip (as : Array α) (bs : Array β) : Array (α × β) :=
 def unzip (as : Array (α × β)) : Array α × Array β :=
   as.foldl (init := (#[], #[])) fun (as, bs) (a, b) => (as.push a, bs.push b)
 
+@[deprecated partition (since := "2024-11-06")]
 def split (as : Array α) (p : α → Bool) : Array α × Array α :=
   as.foldl (init := (#[], #[])) fun (as, bs) a =>
     if p a then (as.push a, bs) else (as, bs.push a)
 
-/-! ### Auxiliary functions used in metaprogramming.
+/-! ## Auxiliary functions used in metaprogramming.
 
-We do not intend to provide verification theorems for these functions.
+We do not currently intend to provide verification theorems for these functions.
 -/
 
+/- ### reduceOption -/
+
+/-- Drop `none`s from a Array, and replace each remaining `some a` with `a`. -/
+@[inline] def reduceOption (as : Array (Option α)) : Array α :=
+  as.filterMap id
+
+/-! ### eraseReps -/
+
+/--
+`O(|l|)`. Erase repeated adjacent elements. Keeps the first occurrence of each run.
+* `eraseReps #[1, 3, 2, 2, 2, 3, 5] = #[1, 3, 2, 3, 5]`
+-/
+def eraseReps {α} [BEq α] (as : Array α) : Array α :=
+  if h : 0 < as.size then
+    let ⟨last, r⟩ := as.foldl (init := (as[0], #[])) fun ⟨last, r⟩ a =>
+      if a == last then ⟨last, r⟩ else ⟨a, r.push last⟩
+    r.push last
+  else
+    #[]
+
+/-! ### allDiff -/
+
 private def allDiffAuxAux [BEq α] (as : Array α) (a : α) : forall (i : Nat), i < as.size → Bool
   | 0,   _ => true
   | i+1, h =>
@@ -832,6 +917,8 @@ decreasing_by simp_wf; decreasing_trivial_pre_omega
 def allDiff [BEq α] (as : Array α) : Bool :=
   allDiffAux as 0
 
+/-! ### getEvenElems -/
+
 @[inline] def getEvenElems (as : Array α) : Array α :=
   (·.2) <| as.foldl (init := (true, Array.empty)) fun (even, r) a =>
     if even then

src/Init/Data/Array/BasicAux.lean

@@ -60,7 +60,7 @@ where
       if ptrEq a b then
         go (i+1) as
       else
-        go (i+1) (as.set ⟨i, h⟩ b)
+        go (i+1) (as.set i b h)
     else
       return as
 

src/Init/Data/Array/BinSearch.lean

@@ -69,8 +69,8 @@ namespace Array
   if as.isEmpty then do let v ← add (); pure <| as.push v
   else if lt k (as.get! 0) then do let v ← add (); pure <| as.insertAt! 0 v
   else if !lt (as.get! 0) k then as.modifyM 0 <| merge
-  else if lt as.back k then do let v ← add (); pure <| as.push v
-  else if !lt k as.back then as.modifyM (as.size - 1) <| merge
+  else if lt as.back! k then do let v ← add (); pure <| as.push v
+  else if !lt k as.back! then as.modifyM (as.size - 1) <| merge
   else binInsertAux lt merge add as k 0 (as.size - 1)
 
 @[inline] def binInsert {α : Type u} (lt : α → α → Bool) (as : Array α) (k : α) : Array α :=

src/Init/Data/Array/Bootstrap.lean

@@ -23,7 +23,7 @@ theorem foldlM_eq_foldlM_toList.aux [Monad m]
   · cases Nat.not_le_of_gt ‹_› (Nat.zero_add _ ▸ H)
   · rename_i i; rw [Nat.succ_add] at H
     simp [foldlM_eq_foldlM_toList.aux f arr i (j+1) H]
-    rw (config := {occs := .pos [2]}) [← List.get_drop_eq_drop _ _ ‹_›]
+    rw (occs := .pos [2]) [← List.getElem_cons_drop_succ_eq_drop ‹_›]
     rfl
   · rw [List.drop_of_length_le (Nat.ge_of_not_lt ‹_›)]; rfl
 
@@ -42,7 +42,7 @@ theorem foldrM_eq_reverse_foldlM_toList.aux [Monad m]
   unfold foldrM.fold
   match i with
   | 0 => simp [List.foldlM, List.take]
-  | i+1 => rw [← List.take_concat_get _ _ h]; simp [← (aux f arr · i)]; rfl
+  | i+1 => rw [← List.take_concat_get _ _ h]; simp [← (aux f arr · i)]
 
 theorem foldrM_eq_reverse_foldlM_toList [Monad m] (f : α → β → m β) (init : β) (arr : Array α) :
     arr.foldrM f init = arr.toList.reverse.foldlM (fun x y => f y x) init := by
@@ -73,12 +73,23 @@ theorem foldr_eq_foldr_toList (f : α → β → β) (init : β) (arr : Array α
 
 @[simp] theorem append_eq_append (arr arr' : Array α) : arr.append arr' = arr ++ arr' := rfl
 
-@[simp] theorem append_toList (arr arr' : Array α) :
+@[simp] theorem toList_append (arr arr' : Array α) :
     (arr ++ arr').toList = arr.toList ++ arr'.toList := by
   rw [← append_eq_append]; unfold Array.append
   rw [foldl_eq_foldl_toList]
   induction arr'.toList generalizing arr <;> simp [*]
 
+@[simp] theorem toList_empty : (#[] : Array α).toList = [] := rfl
+
+@[simp] theorem append_nil (as : Array α) : as ++ #[] = as := by
+  apply ext'; simp only [toList_append, toList_empty, List.append_nil]
+
+@[simp] theorem nil_append (as : Array α) : #[] ++ as = as := by
+  apply ext'; simp only [toList_append, toList_empty, List.nil_append]
+
+@[simp] theorem append_assoc (as bs cs : Array α) : as ++ bs ++ cs = as ++ (bs ++ cs) := by
+  apply ext'; simp only [toList_append, List.append_assoc]
+
 @[simp] theorem appendList_eq_append
     (arr : Array α) (l : List α) : arr.appendList l = arr ++ l := rfl
 
@@ -111,8 +122,8 @@ abbrev toList_eq := @toListImpl_eq
 @[deprecated pop_toList (since := "2024-09-09")]
 abbrev pop_data := @pop_toList
 
-@[deprecated append_toList (since := "2024-09-09")]
-abbrev append_data := @append_toList
+@[deprecated toList_append (since := "2024-09-09")]
+abbrev append_data := @toList_append
 
 @[deprecated appendList_toList (since := "2024-09-09")]
 abbrev appendList_data := @appendList_toList

src/Init/Data/Array/DecidableEq.lean

@@ -6,14 +6,16 @@ Authors: Leonardo de Moura
 prelude
 import Init.Data.Array.Basic
 import Init.Data.BEq
+import Init.Data.Nat.Lemmas
+import Init.Data.List.Nat.BEq
 import Init.ByCases
 
 namespace Array
 
 theorem rel_of_isEqvAux
-    (r : α → α → Bool) (a b : Array α) (hsz : a.size = b.size) (i : Nat) (hi : i ≤ a.size)
+    {r : α → α → Bool} {a b : Array α} (hsz : a.size = b.size) {i : Nat} (hi : i ≤ a.size)
     (heqv : Array.isEqvAux a b hsz r i hi)
-    (j : Nat) (hj : j < i) : r (a[j]'(Nat.lt_of_lt_of_le hj hi)) (b[j]'(Nat.lt_of_lt_of_le hj (hsz ▸ hi))) := by
+    {j : Nat} (hj : j < i) : r (a[j]'(Nat.lt_of_lt_of_le hj hi)) (b[j]'(Nat.lt_of_lt_of_le hj (hsz ▸ hi))) := by
   induction i with
   | zero => contradiction
   | succ i ih =>
@@ -26,15 +28,46 @@ theorem rel_of_isEqvAux
       subst hj'
       exact heqv.left
 
-theorem rel_of_isEqv (r : α → α → Bool) (a b : Array α) :
+theorem isEqvAux_of_rel {r : α → α → Bool} {a b : Array α} (hsz : a.size = b.size) {i : Nat} (hi : i ≤ a.size)
+    (w : ∀ j, (hj : j < i) → r (a[j]'(Nat.lt_of_lt_of_le hj hi)) (b[j]'(Nat.lt_of_lt_of_le hj (hsz ▸ hi)))) : Array.isEqvAux a b hsz r i hi := by
+  induction i with
+  | zero => simp [Array.isEqvAux]
+  | succ i ih =>
+    simp only [isEqvAux, Bool.and_eq_true]
+    exact ⟨w i (Nat.lt_add_one i), ih _ fun j hj => w j (Nat.lt_add_right 1 hj)⟩
+
+theorem rel_of_isEqv {r : α → α → Bool} {a b : Array α} :
     Array.isEqv a b r → ∃ h : a.size = b.size, ∀ (i : Nat) (h' : i < a.size), r (a[i]) (b[i]'(h ▸ h')) := by
   simp only [isEqv]
   split <;> rename_i h
-  · exact fun h' => ⟨h, rel_of_isEqvAux r a b h a.size (Nat.le_refl ..) h'⟩
+  · exact fun h' => ⟨h, fun i => rel_of_isEqvAux h (Nat.le_refl ..) h'⟩
   · intro; contradiction
 
+theorem isEqv_iff_rel (a b : Array α) (r) :
+    Array.isEqv a b r ↔ ∃ h : a.size = b.size, ∀ (i : Nat) (h' : i < a.size), r (a[i]) (b[i]'(h ▸ h')) :=
+  ⟨rel_of_isEqv, fun ⟨h, w⟩ => by
+    simp only [isEqv, ← h, ↓reduceDIte]
+    exact isEqvAux_of_rel h (by simp [h]) w⟩
+
+theorem isEqv_eq_decide (a b : Array α) (r) :
+    Array.isEqv a b r =
+      if h : a.size = b.size then decide (∀ (i : Nat) (h' : i < a.size), r (a[i]) (b[i]'(h ▸ h'))) else false := by
+  by_cases h : Array.isEqv a b r
+  · simp only [h, Bool.true_eq]
+    simp only [isEqv_iff_rel] at h
+    obtain ⟨h, w⟩ := h
+    simp [h, w]
+  · let h' := h
+    simp only [Bool.not_eq_true] at h
+    simp only [h, Bool.false_eq, dite_eq_right_iff, decide_eq_false_iff_not, Classical.not_forall,
+      Bool.not_eq_true]
+    simpa [isEqv_iff_rel] using h'
+
+@[simp] theorem isEqv_toList [BEq α] (a b : Array α) : (a.toList.isEqv b.toList r) = (a.isEqv b r) := by
+  simp [isEqv_eq_decide, List.isEqv_eq_decide]
+
 theorem eq_of_isEqv [DecidableEq α] (a b : Array α) (h : Array.isEqv a b (fun x y => x = y)) : a = b := by
-  have ⟨h, h'⟩ := rel_of_isEqv (fun x y => x = y) a b h
+  have ⟨h, h'⟩ := rel_of_isEqv h
   exact ext _ _ h (fun i lt _ => by simpa using h' i lt)
 
 theorem isEqvAux_self (r : α → α → Bool) (hr : ∀ a, r a a) (a : Array α) (i : Nat) (h : i ≤ a.size) :
@@ -56,4 +89,22 @@ instance [DecidableEq α] : DecidableEq (Array α) :=
     | true  => isTrue (eq_of_isEqv a b h)
     | false => isFalse fun h' => by subst h'; rw [isEqv_self] at h; contradiction
 
+theorem beq_eq_decide [BEq α] (a b : Array α) :
+    (a == b) = if h : a.size = b.size then
+      decide (∀ (i : Nat) (h' : i < a.size), a[i] == b[i]'(h ▸ h')) else false := by
+  simp [BEq.beq, isEqv_eq_decide]
+
+@[simp] theorem beq_toList [BEq α] (a b : Array α) : (a.toList == b.toList) = (a == b) := by
+  simp [beq_eq_decide, List.beq_eq_decide]
+
 end Array
+
+namespace List
+
+@[simp] theorem isEqv_toArray [BEq α] (a b : List α) : (a.toArray.isEqv b.toArray r) = (a.isEqv b r) := by
+  simp [isEqv_eq_decide, Array.isEqv_eq_decide]
+
+@[simp] theorem beq_toArray [BEq α] (a b : List α) : (a.toArray == b.toArray) = (a == b) := by
+  simp [beq_eq_decide, Array.beq_eq_decide]
+
+end List

src/Init/Data/Array/GetLit.lean

@@ -41,6 +41,6 @@ where
   getLit_eq (as : Array α) (i : Nat) (h₁ : as.size = n) (h₂ : i < n) : as.getLit i h₁ h₂ = getElem as.toList i ((id (α := as.toList.length = n) h₁) ▸ h₂) :=
     rfl
   go (i : Nat) (hi : i ≤ as.size) : toListLitAux as n hsz i hi (as.toList.drop i) = as.toList := by
-    induction i <;> simp [getLit_eq, List.get_drop_eq_drop, toListLitAux, List.drop, *]
+    induction i <;> simp only [List.drop, toListLitAux, getLit_eq, List.getElem_cons_drop_succ_eq_drop, *]
 
 end Array

src/Init/Data/Array/MapIdx.lean

@@ -0,0 +1,112 @@
+/-
+Copyright (c) 2022 Mario Carneiro. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Mario Carneiro, Kim Morrison
+-/
+prelude
+import Init.Data.Array.Lemmas
+import Init.Data.List.MapIdx
+
+namespace Array
+
+/-! ### mapFinIdx -/
+
+-- This could also be proved from `SatisfiesM_mapIdxM` in Batteries.
+theorem mapFinIdx_induction (as : Array α) (f : Fin as.size → α → β)
+    (motive : Nat → Prop) (h0 : motive 0)
+    (p : Fin as.size → β → Prop)
+    (hs : ∀ i, motive i.1 → p i (f i as[i]) ∧ motive (i + 1)) :
+    motive as.size ∧ ∃ eq : (Array.mapFinIdx as f).size = as.size,
+      ∀ i h, p ⟨i, h⟩ ((Array.mapFinIdx as f)[i]) := by
+  let rec go {bs i j h} (h₁ : j = bs.size) (h₂ : ∀ i h h', p ⟨i, h⟩ bs[i]) (hm : motive j) :
+    let arr : Array β := Array.mapFinIdxM.map (m := Id) as f i j h bs
+    motive as.size ∧ ∃ eq : arr.size = as.size, ∀ i h, p ⟨i, h⟩ arr[i] := by
+    induction i generalizing j bs with simp [mapFinIdxM.map]
+    | zero =>
+      have := (Nat.zero_add _).symm.trans h
+      exact ⟨this ▸ hm, h₁ ▸ this, fun _ _ => h₂ ..⟩
+    | succ i ih =>
+      apply @ih (bs.push (f ⟨j, by omega⟩ as[j])) (j + 1) (by omega) (by simp; omega)
+      · intro i i_lt h'
+        rw [getElem_push]
+        split
+        · apply h₂
+        · simp only [size_push] at h'
+          obtain rfl : i = j := by omega
+          apply (hs ⟨i, by omega⟩ hm).1
+      · exact (hs ⟨j, by omega⟩ hm).2
+  simp [mapFinIdx, mapFinIdxM]; exact go rfl nofun h0
+
+theorem mapFinIdx_spec (as : Array α) (f : Fin as.size → α → β)
+    (p : Fin as.size → β → Prop) (hs : ∀ i, p i (f i as[i])) :
+    ∃ eq : (Array.mapFinIdx as f).size = as.size,
+      ∀ i h, p ⟨i, h⟩ ((Array.mapFinIdx as f)[i]) :=
+  (mapFinIdx_induction _ _ (fun _ => True) trivial p fun _ _ => ⟨hs .., trivial⟩).2
+
+@[simp] theorem size_mapFinIdx (a : Array α) (f : Fin a.size → α → β) : (a.mapFinIdx f).size = a.size :=
+  (mapFinIdx_spec (p := fun _ _ => True) (hs := fun _ => trivial)).1
+
+@[simp] theorem size_zipWithIndex (as : Array α) : as.zipWithIndex.size = as.size :=
+  Array.size_mapFinIdx _ _
+
+@[simp] theorem getElem_mapFinIdx (a : Array α) (f : Fin a.size → α → β) (i : Nat)
+    (h : i < (mapFinIdx a f).size) :
+    (a.mapFinIdx f)[i] = f ⟨i, by simp_all⟩ (a[i]'(by simp_all)) :=
+  (mapFinIdx_spec _ _ (fun i b => b = f i a[i]) fun _ => rfl).2 i _
+
+@[simp] theorem getElem?_mapFinIdx (a : Array α) (f : Fin a.size → α → β) (i : Nat) :
+    (a.mapFinIdx f)[i]? =
+      a[i]?.pbind fun b h => f ⟨i, (getElem?_eq_some_iff.1 h).1⟩ b := by
+  simp only [getElem?_def, size_mapFinIdx, getElem_mapFinIdx]
+  split <;> simp_all
+
+@[simp] theorem toList_mapFinIdx (a : Array α) (f : Fin a.size → α → β) :
+    (a.mapFinIdx f).toList = a.toList.mapFinIdx (fun i a => f ⟨i, by simp⟩ a) := by
+  apply List.ext_getElem <;> simp
+
+/-! ### mapIdx -/
+
+theorem mapIdx_induction (f : Nat → α → β) (as : Array α)
+    (motive : Nat → Prop) (h0 : motive 0)
+    (p : Fin as.size → β → Prop)
+    (hs : ∀ i, motive i.1 → p i (f i as[i]) ∧ motive (i + 1)) :
+    motive as.size ∧ ∃ eq : (as.mapIdx f).size = as.size,
+      ∀ i h, p ⟨i, h⟩ ((as.mapIdx f)[i]) :=
+  mapFinIdx_induction as (fun i a => f i a) motive h0 p hs
+
+theorem mapIdx_spec (f : Nat → α → β) (as : Array α)
+    (p : Fin as.size → β → Prop) (hs : ∀ i, p i (f i as[i])) :
+    ∃ eq : (as.mapIdx f).size = as.size,
+      ∀ i h, p ⟨i, h⟩ ((as.mapIdx f)[i]) :=
+  (mapIdx_induction _ _ (fun _ => True) trivial p fun _ _ => ⟨hs .., trivial⟩).2
+
+@[simp] theorem size_mapIdx (f : Nat → α → β) (as : Array α) : (as.mapIdx f).size = as.size :=
+  (mapIdx_spec (p := fun _ _ => True) (hs := fun _ => trivial)).1
+
+@[simp] theorem getElem_mapIdx (f : Nat → α → β) (as : Array α) (i : Nat)
+    (h : i < (as.mapIdx f).size) :
+    (as.mapIdx f)[i] = f i (as[i]'(by simp_all)) :=
+  (mapIdx_spec _ _ (fun i b => b = f i as[i]) fun _ => rfl).2 i (by simp_all)
+
+@[simp] theorem getElem?_mapIdx (f : Nat → α → β) (as : Array α) (i : Nat) :
+    (as.mapIdx f)[i]? =
+      as[i]?.map (f i) := by
+  simp [getElem?_def, size_mapIdx, getElem_mapIdx]
+
+@[simp] theorem toList_mapIdx (f : Nat → α → β) (as : Array α) :
+    (as.mapIdx f).toList = as.toList.mapIdx (fun i a => f i a) := by
+  apply List.ext_getElem <;> simp
+
+end Array
+
+namespace List
+
+@[simp] theorem mapFinIdx_toArray (l : List α) (f : Fin l.length → α → β) :
+    l.toArray.mapFinIdx f = (l.mapFinIdx f).toArray := by
+  ext <;> simp
+
+@[simp] theorem mapIdx_toArray (f : Nat → α → β) (l : List α) :
+    l.toArray.mapIdx f = (l.mapIdx f).toArray := by
+  ext <;> simp
+
+end List

src/Init/Data/Array/Mem.lean

@@ -10,25 +10,16 @@ import Init.Data.List.BasicAux
 
 namespace Array
 
-/-- `a ∈ as` is a predicate which asserts that `a` is in the array `as`. -/
--- NB: This is defined as a structure rather than a plain def so that a lemma
--- like `sizeOf_lt_of_mem` will not apply with no actual arrays around.
-structure Mem (as : Array α) (a : α) : Prop where
-  val : a ∈ as.toList
-
-instance : Membership α (Array α) where
-  mem := Mem
-
 theorem sizeOf_lt_of_mem [SizeOf α] {as : Array α} (h : a ∈ as) : sizeOf a < sizeOf as := by
   cases as with | _ as =>
   exact Nat.lt_trans (List.sizeOf_lt_of_mem h.val) (by simp_arith)
 
-theorem sizeOf_get [SizeOf α] (as : Array α) (i : Fin as.size) : sizeOf (as.get i) < sizeOf as := by
+theorem sizeOf_get [SizeOf α] (as : Array α) (i : Nat) (h : i < as.size) : sizeOf (as.get i h) < sizeOf as := by
   cases as with | _ as =>
-  exact Nat.lt_trans (List.sizeOf_get ..) (by simp_arith)
+  simpa using Nat.lt_trans (List.sizeOf_get _ ⟨i, h⟩) (by simp_arith)
 
 @[simp] theorem sizeOf_getElem [SizeOf α] (as : Array α) (i : Nat) (h : i < as.size) :
-  sizeOf (as[i]'h) < sizeOf as := sizeOf_get _ _
+  sizeOf (as[i]'h) < sizeOf as := sizeOf_get _ _ h
 
 /-- This tactic, added to the `decreasing_trivial` toolbox, proves that
 `sizeOf arr[i] < sizeOf arr`, which is useful for well founded recursions

src/Init/Data/Array/QSort.lean

@@ -5,6 +5,7 @@ Authors: Leonardo de Moura
 -/
 prelude
 import Init.Data.Array.Basic
+import Init.Data.Ord
 
 namespace Array
 -- TODO: remove the [Inhabited α] parameters as soon as we have the tactic framework for automating proof generation and using Array.fget
@@ -44,4 +45,11 @@ def qpartition (as : Array α) (lt : α → α → Bool) (lo hi : Nat) : Nat ×
     else as
   sort as low high
 
+set_option linter.unusedVariables.funArgs false in
+/--
+Sort an array using `compare` to compare elements.
+-/
+def qsortOrd [ord : Ord α] (xs : Array α) : Array α :=
+  xs.qsort fun x y => compare x y |>.isLT
+
 end Array

src/Init/Data/Array/Set.lean

@@ -0,0 +1,39 @@
+/-
+Copyright (c) 2020 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Leonardo de Moura, Mario Carneiro
+-/
+prelude
+import Init.Tactics
+
+
+/--
+Set an element in an array, using a proof that the index is in bounds.
+(This proof can usually be omitted, and will be synthesized automatically.)
+
+This will perform the update destructively provided that `a` has a reference
+count of 1 when called.
+-/
+@[extern "lean_array_fset"]
+def Array.set (a : Array α) (i : @& Nat) (v : α) (h : i < a.size := by get_elem_tactic) :
+    Array α where
+  toList := a.toList.set i v
+
+/--
+Set an element in an array, or do nothing if the index is out of bounds.
+
+This will perform the update destructively provided that `a` has a reference
+count of 1 when called.
+-/
+@[inline] def Array.setD (a : Array α) (i : Nat) (v : α) : Array α :=
+  dite (LT.lt i a.size) (fun h => a.set i v h) (fun _ => a)
+
+/--
+Set an element in an array, or panic if the index is out of bounds.
+
+This will perform the update destructively provided that `a` has a reference
+count of 1 when called.
+-/
+@[extern "lean_array_set"]
+def Array.set! (a : Array α) (i : @& Nat) (v : α) : Array α :=
+  Array.setD a i v

src/Init/Data/Array/Subarray.lean

@@ -48,7 +48,7 @@ instance : GetElem (Subarray α) Nat α fun xs i => i < xs.size where
   getElem xs i h := xs.get ⟨i, h⟩
 
 @[inline] def getD (s : Subarray α) (i : Nat) (v₀ : α) : α :=
-  if h : i < s.size then s.get ⟨i, h⟩ else v₀
+  if h : i < s.size then s[i] else v₀
 
 abbrev get! [Inhabited α] (s : Subarray α) (i : Nat) : α :=
   getD s i default
@@ -59,6 +59,22 @@ def popFront (s : Subarray α) : Subarray α :=
   else
     s
 
+/--
+The empty subarray.
+-/
+protected def empty : Subarray α where
+  array := #[]
+  start := 0
+  stop := 0
+  start_le_stop := Nat.le_refl 0
+  stop_le_array_size := Nat.le_refl 0
+
+instance : EmptyCollection (Subarray α) :=
+  ⟨Subarray.empty⟩
+
+instance : Inhabited (Subarray α) :=
+  ⟨{}⟩
+
 @[inline] unsafe def forInUnsafe {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m] (s : Subarray α) (b : β) (f : α → β → m (ForInStep β)) : m β :=
   let sz := USize.ofNat s.stop
   let rec @[specialize] loop (i : USize) (b : β) : m β := do

src/Init/Data/Array/TakeDrop.lean

@@ -12,7 +12,7 @@ namespace Array
 theorem exists_of_uset (self : Array α) (i d h) :
     ∃ l₁ l₂, self.toList = l₁ ++ self[i] :: l₂ ∧ List.length l₁ = i.toNat ∧
       (self.uset i d h).toList = l₁ ++ d :: l₂ := by
-  simpa only [ugetElem_eq_getElem, getElem_eq_toList_getElem, uset, toList_set] using
+  simpa only [ugetElem_eq_getElem, getElem_eq_getElem_toList, uset, toList_set] using
     List.exists_of_set _
 
 end Array

src/Init/Data/BitVec/Basic.lean

@@ -1,19 +1,20 @@
 /-
 Copyright (c) 2024 Lean FRO, LLC. All rights reserved.
 Released under Apache 2.0 license as described in the file LICENSE.
-Authors: Joe Hendrix, Wojciech Nawrocki, Leonardo de Moura, Mario Carneiro, Alex Keizer, Harun Khan, Abdalrhman M Mohamed
+Authors: Joe Hendrix, Wojciech Nawrocki, Leonardo de Moura, Mario Carneiro, Alex Keizer, Harun Khan, Abdalrhman M Mohamed, Siddharth Bhat
 -/
 prelude
 import Init.Data.Fin.Basic
 import Init.Data.Nat.Bitwise.Lemmas
 import Init.Data.Nat.Power2
 import Init.Data.Int.Bitwise
+import Init.Data.BitVec.BasicAux
 
 /-!
-We define bitvectors. We choose the `Fin` representation over others for its relative efficiency
-(Lean has special support for `Nat`), alignment with `UIntXY` types which are also represented
-with `Fin`, and the fact that bitwise operations on `Fin` are already defined. Some other possible
-representations are `List Bool`, `{ l : List Bool // l.length = w }`, `Fin w → Bool`.
+We define the basic algebraic structure of bitvectors. We choose the `Fin` representation over
+others for its relative efficiency (Lean has special support for `Nat`),  and the fact that bitwise
+operations on `Fin` are already defined. Some other possible representations are `List Bool`,
+`{ l : List Bool // l.length = w }`, `Fin w → Bool`.
 
 We define many of the bitvector operations from the
 [`QF_BV` logic](https://smtlib.cs.uiowa.edu/logics-all.shtml#QF_BV).
@@ -22,60 +23,12 @@ of SMT-LIBv2.
 
 set_option linter.missingDocs true
 
-/--
-A bitvector of the specified width.
-
-This is represented as the underlying `Nat` number in both the runtime
-and the kernel, inheriting all the special support for `Nat`.
--/
-structure BitVec (w : Nat) where
-  /-- Construct a `BitVec w` from a number less than `2^w`.
-  O(1), because we use `Fin` as the internal representation of a bitvector. -/
-  ofFin ::
-  /-- Interpret a bitvector as a number less than `2^w`.
-  O(1), because we use `Fin` as the internal representation of a bitvector. -/
-  toFin : Fin (2^w)
-
-/--
-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 (x y : BitVec n) : Decidable (x = y) :=
-  match x, y with
-  | ⟨n⟩, ⟨m⟩ =>
-    if h : n = m then
-      isTrue (h ▸ rfl)
-    else
-      isFalse (fun h' => BitVec.noConfusion h' (fun h' => absurd h' h))
-
-instance : DecidableEq (BitVec n) := BitVec.decEq
-
 namespace BitVec
 
 section Nat
 
-/-- The `BitVec` with value `i`, given a proof that `i < 2^n`. -/
-@[match_pattern]
-protected def ofNatLt {n : Nat} (i : Nat) (p : i < 2^n) : BitVec n where
-  toFin := ⟨i, p⟩
-
-/-- The `BitVec` with value `i mod 2^n`. -/
-@[match_pattern]
-protected def ofNat (n : Nat) (i : Nat) : BitVec n where
-  toFin := Fin.ofNat' (2^n) i
-
-instance instOfNat : OfNat (BitVec n) i where ofNat := .ofNat n i
 instance natCastInst : NatCast (BitVec w) := ⟨BitVec.ofNat w⟩
 
-/-- 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 (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
-
 @[deprecated isLt (since := "2024-03-12")]
 theorem toNat_lt (x : BitVec n) : x.toNat < 2^n := x.isLt
 
@@ -238,22 +191,6 @@ end repr_toString
 
 section arithmetic
 
-/--
-Addition for bit vectors. This can be interpreted as either signed or unsigned addition
-modulo `2^n`.
-
-SMT-Lib name: `bvadd`.
--/
-protected def add (x y : BitVec n) : BitVec n := .ofNat n (x.toNat + y.toNat)
-instance : Add (BitVec n) := ⟨BitVec.add⟩
-
-/--
-Subtraction for bit vectors. This can be interpreted as either signed or unsigned subtraction
-modulo `2^n`.
--/
-protected def sub (x y : BitVec n) : BitVec n := .ofNat n ((2^n - y.toNat) + x.toNat)
-instance : Sub (BitVec n) := ⟨BitVec.sub⟩
-
 /--
 Negation for bit vectors. This can be interpreted as either signed or unsigned negation
 modulo `2^n`.
@@ -269,8 +206,8 @@ Return the absolute value of a signed bitvector.
 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
-modulo `2^n`.
+Multiplication for bit vectors. This can be interpreted as either signed or unsigned
+multiplication modulo `2^n`.
 
 SMT-Lib name: `bvmul`.
 -/
@@ -387,10 +324,6 @@ SMT-Lib name: `bvult`.
 -/
 protected def ult (x y : BitVec n) : Bool := x.toNat < y.toNat
 
-instance : LT (BitVec n) where lt := (·.toNat < ·.toNat)
-instance (x y : BitVec n) : Decidable (x < y) :=
-  inferInstanceAs (Decidable (x.toNat < y.toNat))
-
 /--
 Unsigned less-than-or-equal-to for bit vectors.
 
@@ -398,10 +331,6 @@ SMT-Lib name: `bvule`.
 -/
 protected def ule (x y : BitVec n) : Bool := x.toNat ≤ y.toNat
 
-instance : LE (BitVec n) where le := (·.toNat ≤ ·.toNat)
-instance (x y : BitVec n) : Decidable (x ≤ y) :=
-  inferInstanceAs (Decidable (x.toNat ≤ y.toNat))
-
 /--
 Signed less-than for bit vectors.
 
@@ -676,6 +605,13 @@ result of appending a single bit to the front in the naive implementation).
     That is, the new bit is the least significant bit. -/
 def concat {n} (msbs : BitVec n) (lsb : Bool) : BitVec (n+1) := msbs ++ (ofBool lsb)
 
+/--
+`x.shiftConcat b` shifts all bits of `x` to the left by `1` and sets the least significant bit to `b`.
+It is a non-dependent version of `concat` that does not change the total bitwidth.
+-/
+def shiftConcat (x : BitVec n) (b : Bool) : BitVec n :=
+  (x.concat b).truncate n
+
 /-- Prepend a single bit to the front of a bitvector, using big endian order (see `append`).
     That is, the new bit is the most significant bit. -/
 def cons {n} (msb : Bool) (lsbs : BitVec n) : BitVec (n+1) :=
@@ -698,6 +634,16 @@ def twoPow (w : Nat) (i : Nat) : BitVec w := 1#w <<< i
 
 end bitwise
 
+/-- Compute a hash of a bitvector, combining 64-bit words using `mixHash`. -/
+def hash (bv : BitVec n) : UInt64 :=
+  if n ≤ 64 then
+    bv.toFin.val.toUInt64
+  else
+    mixHash (bv.toFin.val.toUInt64) (hash ((bv >>> 64).setWidth (n - 64)))
+
+instance : Hashable (BitVec n) where
+  hash := hash
+
 section normalization_eqs
 /-! We add simp-lemmas that rewrite bitvector operations into the equivalent notation -/
 @[simp] theorem append_eq (x : BitVec w) (y : BitVec v)   : BitVec.append x y = x ++ y        := rfl
@@ -711,6 +657,8 @@ section normalization_eqs
 @[simp] theorem add_eq (x y : BitVec w)                   : BitVec.add x y = x + y            := rfl
 @[simp] theorem sub_eq (x y : BitVec w)                   : BitVec.sub x y = x - y            := rfl
 @[simp] theorem mul_eq (x y : BitVec w)                   : BitVec.mul x y = x * y            := rfl
+@[simp] theorem udiv_eq (x y : BitVec w)                  : BitVec.udiv x y = x / y           := rfl
+@[simp] theorem umod_eq (x y : BitVec w)                  : BitVec.umod x y = x % y           := rfl
 @[simp] theorem zero_eq                                   : BitVec.zero n = 0#n               := rfl
 end normalization_eqs
 

src/Init/Data/BitVec/BasicAux.lean

@@ -0,0 +1,52 @@
+/-
+Copyright (c) 2024 Lean FRO, LLC. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Joe Hendrix, Wojciech Nawrocki, Leonardo de Moura, Mario Carneiro, Alex Keizer, Harun Khan, Abdalrhman M Mohamed
+-/
+prelude
+import Init.Data.Fin.Basic
+
+set_option linter.missingDocs true
+
+/-!
+This module exists to provide the very basic `BitVec` definitions required for
+`Init.Data.UInt.BasicAux`.
+-/
+
+namespace BitVec
+
+section Nat
+
+/-- The `BitVec` with value `i mod 2^n`. -/
+@[match_pattern]
+protected def ofNat (n : Nat) (i : Nat) : BitVec n where
+  toFin := Fin.ofNat' (2^n) i
+
+instance instOfNat : OfNat (BitVec n) i where ofNat := .ofNat n i
+
+/-- Return the bound in terms of toNat. -/
+theorem isLt (x : BitVec w) : x.toNat < 2^w := x.toFin.isLt
+
+end Nat
+
+section arithmetic
+
+/--
+Addition for bit vectors. This can be interpreted as either signed or unsigned addition
+modulo `2^n`.
+
+SMT-Lib name: `bvadd`.
+-/
+protected def add (x y : BitVec n) : BitVec n := .ofNat n (x.toNat + y.toNat)
+instance : Add (BitVec n) := ⟨BitVec.add⟩
+
+/--
+Subtraction for bit vectors. This can be interpreted as either signed or unsigned subtraction
+modulo `2^n`.
+-/
+protected def sub (x y : BitVec n) : BitVec n := .ofNat n ((2^n - y.toNat) + x.toNat)
+instance : Sub (BitVec n) := ⟨BitVec.sub⟩
+
+end arithmetic
+
+end BitVec

src/Init/Data/BitVec/Bitblast.lean

@@ -1,7 +1,7 @@
 /-
 Copyright (c) 2024 Lean FRO, LLC. All rights reserved.
 Released under Apache 2.0 license as described in the file LICENSE.
-Authors: Harun Khan, Abdalrhman M Mohamed, Joe Hendrix
+Authors: Harun Khan, Abdalrhman M Mohamed, Joe Hendrix, Siddharth Bhat
 -/
 prelude
 import Init.Data.BitVec.Folds
@@ -18,6 +18,80 @@ as vectors of bits into proofs about Lean `BitVec` values.
 The module is named for the bit-blasting operation in an SMT solver that converts bitvector
 expressions into expressions about individual bits in each vector.
 
+### Example: How bitblasting works for multiplication
+
+We explain how the lemmas here are used for bitblasting,
+by using multiplication as a prototypical example.
+Other bitblasters for other operations follow the same pattern.
+To bitblast a multiplication of the form `x * y`,
+we must unfold the above into a form that the SAT solver understands.
+
+We assume that the solver already knows how to bitblast addition.
+This is known to `bv_decide`, by exploiting the lemma `add_eq_adc`,
+which says that `x + y : BitVec w` equals `(adc x y false).2`,
+where `adc` builds an add-carry circuit in terms of the primitive operations
+(bitwise and, bitwise or, bitwise xor) that bv_decide already understands.
+In this way, we layer bitblasters on top of each other,
+by reducing the multiplication bitblaster to an addition operation.
+
+The core lemma is given by `getLsbD_mul`:
+
+```lean
+ x y : BitVec w ⊢ (x * y).getLsbD i = (mulRec x y w).getLsbD i
+```
+
+Which says that the `i`th bit of `x * y` can be obtained by
+evaluating the `i`th bit of `(mulRec x y w)`.
+Once again, we assume that `bv_decide` knows how to implement `getLsbD`,
+given that `mulRec` can be understood by `bv_decide`.
+
+We write two lemmas to enable `bv_decide` to unfold `(mulRec x y w)`
+into a complete circuit, **when `w` is a known constant**`.
+This is given by two recurrence lemmas, `mulRec_zero_eq` and `mulRec_succ_eq`,
+which are applied repeatedly when the width is `0` and when the width is `w' + 1`:
+
+```lean
+mulRec_zero_eq :
+    mulRec x y 0 =
+      if y.getLsbD 0 then x else 0
+
+mulRec_succ_eq
+    mulRec x y (s + 1) =
+      mulRec x y s +
+      if y.getLsbD (s + 1) then (x <<< (s + 1)) else 0 := rfl
+```
+
+By repeatedly applying the lemmas `mulRec_zero_eq` and `mulRec_succ_eq`,
+one obtains a circuit for multiplication.
+Note that this circuit uses `BitVec.add`, `BitVec.getLsbD`, `BitVec.shiftLeft`.
+Here, `BitVec.add` and `BitVec.shiftLeft` are (recursively) bitblasted by `bv_decide`,
+using the lemmas `add_eq_adc` and `shiftLeft_eq_shiftLeftRec`,
+and `BitVec.getLsbD` is a primitive that `bv_decide` knows how to reduce to SAT.
+
+The two lemmas, `mulRec_zero_eq`, and `mulRec_succ_eq`,
+are used in `Std.Tactic.BVDecide.BVExpr.bitblast.blastMul`
+to prove the correctness of the circuit that is built by `bv_decide`.
+
+```lean
+def blastMul (aig : AIG BVBit) (input : AIG.BinaryRefVec aig w) : AIG.RefVecEntry BVBit w
+theorem denote_blastMul (aig : AIG BVBit) (lhs rhs : BitVec w) (assign : Assignment) :
+   ...
+   ⟦(blastMul aig input).aig, (blastMul aig input).vec[idx], assign.toAIGAssignment⟧
+     =
+   (lhs * rhs).getLsbD idx
+```
+
+The definition and theorem above are internal to `bv_decide`,
+and use `mulRec_{zero,succ}_eq` to prove that the circuit built by `bv_decide`
+computes the correct value for multiplication.
+
+To zoom out, therefore, we follow two steps:
+First, we prove bitvector lemmas to unfold a high-level operation (such as multiplication)
+into already bitblastable operations (such as addition and left shift).
+We then use these lemmas to prove the correctness of the circuit that `bv_decide` builds.
+
+We use this workflow to implement bitblasting for all SMT-LIB2 operations.
+
 ## Main results
 * `x + y : BitVec w` is `(adc x y false).2`.
 
@@ -100,6 +174,30 @@ 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)
 
+theorem carry_succ_one (i : Nat) (x : BitVec w) (h : 0 < w) :
+    carry (i+1) x (1#w) false = decide (∀ j ≤ i, x.getLsbD j = true) := by
+  induction i with
+  | zero => simp [carry_succ, h]
+  | succ i ih =>
+    rw [carry_succ, ih]
+    simp only [getLsbD_one, add_one_ne_zero, decide_false, Bool.and_false, atLeastTwo_false_mid]
+    cases hx : x.getLsbD (i+1)
+    case false =>
+      have : ∃ j ≤ i + 1, x.getLsbD j = false :=
+        ⟨i+1, by omega, hx⟩
+      simpa
+    case true =>
+      suffices
+          (∀ (j : Nat), j ≤ i → x.getLsbD j = true)
+          ↔ (∀ (j : Nat), j ≤ i + 1 → x.getLsbD j = true) by
+        simpa
+      constructor
+      · intro h j hj
+        rcases Nat.le_or_eq_of_le_succ hj with (hj' | rfl)
+        · apply h; assumption
+        · exact hx
+      · intro h j hj; apply h; 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
@@ -151,7 +249,7 @@ theorem getLsbD_add_add_bool {i : Nat} (i_lt : i < w) (x y : BitVec w) (c : Bool
     [ Nat.testBit_mod_two_pow,
       Nat.testBit_mul_two_pow_add_eq,
       i_lt,
-      decide_True,
+      decide_true,
       Bool.true_and,
       Nat.add_assoc,
       Nat.add_left_comm (_%_) (_ * _) _,
@@ -164,6 +262,17 @@ theorem getLsbD_add {i : Nat} (i_lt : i < w) (x y : BitVec w) :
       (getLsbD x i ^^ (getLsbD y i ^^ carry i x y false)) := by
   simpa using getLsbD_add_add_bool i_lt x y false
 
+theorem getElem_add_add_bool {i : Nat} (i_lt : i < w) (x y : BitVec w) (c : Bool) :
+    (x + y + setWidth w (ofBool c))[i] =
+      (x[i] ^^ (y[i] ^^ carry i x y c)) := by
+  simp only [← getLsbD_eq_getElem]
+  rw [getLsbD_add_add_bool]
+  omega
+
+theorem getElem_add {i : Nat} (i_lt : i < w) (x y : BitVec w) :
+    (x + y)[i] = (x[i] ^^ (y[i] ^^ carry i x y false)) := by
+  simpa using getElem_add_add_bool i_lt x y false
+
 theorem adc_spec (x y : BitVec w) (c : Bool) :
     adc x y c = (carry w x y c, x + y + setWidth w (ofBool c)) := by
   simp only [adc]
@@ -182,6 +291,21 @@ theorem add_eq_adc (w : Nat) (x y : BitVec w) : x + y = (adc x y false).snd := b
 
 /-! ### add -/
 
+theorem getMsbD_add {i : Nat} {i_lt : i < w} {x y : BitVec w} :
+    getMsbD (x + y) i =
+      Bool.xor (getMsbD x i) (Bool.xor (getMsbD y i) (carry (w - 1 - i) x y false)) := by
+  simp [getMsbD, getLsbD_add, i_lt, show w - 1 - i < w by omega]
+
+theorem msb_add {w : Nat} {x y: BitVec w} :
+    (x + y).msb =
+      Bool.xor x.msb (Bool.xor y.msb (carry (w - 1) x y false)) := by
+  simp only [BitVec.msb, BitVec.getMsbD]
+  by_cases h : w ≤ 0
+  · simp [h, show w = 0 by omega]
+  · rw [getLsbD_add (x := x)]
+    simp [show w > 0 by omega]
+    omega
+
 /-- Adding a bitvector to its own complement yields the all ones bitpattern -/
 @[simp] theorem add_not_self (x : BitVec w) : x + ~~~x = allOnes w := by
   rw [add_eq_adc, adc, iunfoldr_replace (fun _ => false) (allOnes w)]
@@ -207,6 +331,26 @@ theorem add_eq_or_of_and_eq_zero {w : Nat} (x y : BitVec w)
       simp_all [hx]
     · by_cases hx : x.getLsbD i <;> simp_all [hx]
 
+/-! ### Sub-/
+
+theorem getLsbD_sub {i : Nat} {i_lt : i < w} {x y : BitVec w} :
+    (x - y).getLsbD i
+      = (x.getLsbD i ^^ ((~~~y + 1#w).getLsbD i ^^ carry i x (~~~y + 1#w) false)) := by
+  rw [sub_toAdd, BitVec.neg_eq_not_add, getLsbD_add]
+  omega
+
+theorem getMsbD_sub {i : Nat} {i_lt : i < w} {x y : BitVec w} :
+    (x - y).getMsbD i =
+      (x.getMsbD i ^^ ((~~~y + 1).getMsbD i ^^ carry (w - 1 - i) x (~~~y + 1) false)) := by
+  rw [sub_toAdd, neg_eq_not_add, getMsbD_add]
+  · rfl
+  · omega
+
+theorem msb_sub {x y: BitVec w} :
+    (x - y).msb
+      = (x.msb ^^ ((~~~y + 1#w).msb ^^ carry (w - 1 - 0) x (~~~y + 1#w) false)) := by
+  simp [sub_toAdd, BitVec.neg_eq_not_add, msb_add]
+
 /-! ### Negation -/
 
 theorem bit_not_testBit (x : BitVec w) (i : Fin w) :
@@ -232,6 +376,117 @@ theorem bit_neg_eq_neg (x : BitVec w) : -x = (adc (((iunfoldr (fun (i : Fin w) c
     simp [← sub_toAdd, BitVec.sub_add_cancel]
   · simp [bit_not_testBit x _]
 
+/--
+Remember that negating a bitvector is equal to incrementing the complement
+by one, i.e., `-x = ~~~x + 1`. See also `neg_eq_not_add`.
+
+This computation has two crucial properties:
+- The least significant bit of `-x` is the same as the least significant bit of `x`, and
+- The `i+1`-th least significant bit of `-x` is the complement of the `i+1`-th bit of `x`, unless
+  all of the preceding bits are `false`, in which case the bit is equal to the `i+1`-th bit of `x`
+-/
+theorem getLsbD_neg {i : Nat} {x : BitVec w} :
+    getLsbD (-x) i =
+      (getLsbD x i ^^ decide (i < w) && decide (∃ j < i, getLsbD x j = true)) := by
+  rw [neg_eq_not_add]
+  by_cases hi : i < w
+  · rw [getLsbD_add hi]
+    have : 0 < w := by omega
+    simp only [getLsbD_not, hi, decide_true, Bool.true_and, getLsbD_one, this, not_bne,
+      _root_.true_and, not_eq_eq_eq_not]
+    cases i with
+    | zero =>
+      have carry_zero : carry 0 ?x ?y false = false := by
+        simp [carry]; omega
+      simp [hi, carry_zero]
+    | succ =>
+      rw [carry_succ_one _ _ (by omega), ← Bool.xor_not, ← decide_not]
+      simp only [add_one_ne_zero, decide_false, getLsbD_not, and_eq_true, decide_eq_true_eq,
+        not_eq_eq_eq_not, Bool.not_true, false_bne, not_exists, _root_.not_and, not_eq_true,
+        bne_left_inj, decide_eq_decide]
+      constructor
+      · rintro h j hj; exact And.right <| h j (by omega)
+      · rintro h j hj; exact ⟨by omega, h j (by omega)⟩
+  · have h_ge : w ≤ i := by omega
+    simp [getLsbD_ge _ _ h_ge, h_ge, hi]
+
+theorem getMsbD_neg {i : Nat} {x : BitVec w} :
+    getMsbD (-x) i =
+      (getMsbD x i ^^ decide (∃ j < w, i < j ∧ getMsbD x j = true)) := by
+  simp only [getMsbD, getLsbD_neg, Bool.decide_and, Bool.and_eq_true, decide_eq_true_eq]
+  by_cases hi : i < w
+  case neg =>
+    simp [hi]; omega
+  case pos =>
+    have h₁ : w - 1 - i < w := by omega
+    simp only [hi, decide_true, h₁, Bool.true_and, Bool.bne_left_inj, decide_eq_decide]
+    constructor
+    · rintro ⟨j, hj, h⟩
+      refine ⟨w - 1 - j, by omega, by omega, by omega, _root_.cast ?_ h⟩
+      congr; omega
+    · rintro ⟨j, hj₁, hj₂, -, h⟩
+      exact ⟨w - 1 - j, by omega, h⟩
+
+theorem msb_neg {w : Nat} {x : BitVec w} :
+    (-x).msb = ((x != 0#w && x != intMin w) ^^ x.msb) := by
+  simp only [BitVec.msb, getMsbD_neg]
+  by_cases hmin : x = intMin _
+  case pos =>
+    have : (∃ j, j < w ∧ 0 < j ∧ 0 < w ∧ j = 0) ↔ False := by
+      simp; omega
+    simp [hmin, getMsbD_intMin, this]
+  case neg =>
+    by_cases hzero : x = 0#w
+    case pos => simp [hzero]
+    case neg =>
+      have w_pos : 0 < w := by
+        cases w
+        · rw [@of_length_zero x] at hzero
+          contradiction
+        · omega
+      suffices ∃ j, j < w ∧ 0 < j ∧ x.getMsbD j = true
+        by simp [show x != 0#w by simpa, show x != intMin w by simpa, this]
+      false_or_by_contra
+      rename_i getMsbD_x
+      simp only [not_exists, _root_.not_and, not_eq_true] at getMsbD_x
+      /- `getMsbD` says that all bits except the msb are `false` -/
+      cases hmsb : x.msb
+      case true =>
+        apply hmin
+        apply eq_of_getMsbD_eq
+        rintro ⟨i, hi⟩
+        simp only [getMsbD_intMin, w_pos, decide_true, Bool.true_and]
+        cases i
+        case zero => exact hmsb
+        case succ => exact getMsbD_x _ hi (by omega)
+      case false =>
+        apply hzero
+        apply eq_of_getMsbD_eq
+        rintro ⟨i, hi⟩
+        simp only [getMsbD_zero]
+        cases i
+        case zero => exact hmsb
+        case succ => exact getMsbD_x _ hi (by omega)
+
+/-! ### abs -/
+
+theorem msb_abs {w : Nat} {x : BitVec w} :
+    x.abs.msb = (decide (x = intMin w) && decide (0 < w)) := by
+  simp only [BitVec.abs, getMsbD_neg, ne_eq, decide_not, Bool.not_bne]
+  by_cases h₀ : 0 < w
+  · by_cases h₁ : x = intMin w
+    · simp [h₁, msb_intMin]
+    · simp only [neg_eq, h₁, decide_false]
+      by_cases h₂ : x.msb
+      · simp [h₂, msb_neg]
+        and_intros
+        · by_cases h₃ : x = 0#w
+          · simp [h₃] at h₂
+          · simp [h₃]
+        · simp [h₁]
+      · simp [h₂]
+  · simp [BitVec.msb, show w = 0 by omega]
+
 /-! ### Inequalities (le / lt) -/
 
 theorem ult_eq_not_carry (x y : BitVec w) : x.ult y = !carry w x (~~~y) true := by
@@ -311,18 +566,18 @@ theorem setWidth_setWidth_succ_eq_setWidth_setWidth_add_twoPow (x : BitVec w) (i
       setWidth w (x.setWidth i) + (x &&& twoPow w i) := by
   rw [add_eq_or_of_and_eq_zero]
   · ext k
-    simp only [getLsbD_setWidth, Fin.is_lt, decide_True, Bool.true_and, getLsbD_or, getLsbD_and]
+    simp only [getLsbD_setWidth, Fin.is_lt, decide_true, Bool.true_and, getLsbD_or, getLsbD_and]
     by_cases hik : i = k
     · subst hik
       simp
-    · simp only [getLsbD_twoPow, hik, decide_False, Bool.and_false, Bool.or_false]
+    · simp only [getLsbD_twoPow, hik, decide_false, Bool.and_false, Bool.or_false]
       by_cases hik' : k < (i + 1)
       · have hik'' : k < i := by omega
         simp [hik', hik'']
       · have hik'' : ¬ (k < i) := by omega
         simp [hik', hik'']
   · ext k
-    simp only [and_twoPow, getLsbD_and, getLsbD_setWidth, Fin.is_lt, decide_True, Bool.true_and,
+    simp only [and_twoPow, getLsbD_and, getLsbD_setWidth, Fin.is_lt, decide_true, Bool.true_and,
       getLsbD_zero, and_eq_false_imp, and_eq_true, decide_eq_true_eq, and_imp]
     by_cases hi : x.getLsbD i <;> simp [hi] <;> omega
 
@@ -368,6 +623,10 @@ theorem getLsbD_mul (x y : BitVec w) (i : Nat) :
   · simp
   · omega
 
+theorem getElem_mul {x y : BitVec w} {i : Nat} (h : i < w) :
+    (x * y)[i] = (mulRec x y w)[i] := by
+  simp [mulRec_eq_mul_signExtend_setWidth]
+
 /-! ## shiftLeft recurrence for bitblasting -/
 
 /--
@@ -438,6 +697,385 @@ theorem shiftLeft_eq_shiftLeftRec (x : BitVec w₁) (y : BitVec w₂) :
   · simp [of_length_zero]
   · simp [shiftLeftRec_eq]
 
+/-! # udiv/urem recurrence for bitblasting
+
+In order to prove the correctness of the division algorithm on the integers,
+one shows that `n.div d = q` and `n.mod d = r` iff `n = d * q + r` and `0 ≤ r < d`.
+Mnemonic: `n` is the numerator, `d` is the denominator, `q` is the quotient, and `r` the remainder.
+
+This *uniqueness of decomposition* is not true for bitvectors.
+For `n = 0, d = 3, w = 3`, we can write:
+- `0 = 0 * 3 + 0` (`q = 0`, `r = 0 < 3`.)
+- `0 = 2 * 3 + 2 = 6 + 2 ≃ 0 (mod 8)` (`q = 2`, `r = 2 < 3`).
+
+Such examples can be created by choosing different `(q, r)` for a fixed `(d, n)`
+such that `(d * q + r)` overflows and wraps around to equal `n`.
+
+This tells us that the division algorithm must have more restrictions than just the ones
+we have for integers. These restrictions are captured in `DivModState.Lawful`.
+The key idea is to state the relationship in terms of the toNat values of {n, d, q, r}.
+If the division equation `d.toNat * q.toNat + r.toNat = n.toNat` holds,
+then `n.udiv d = q` and `n.umod d = r`.
+
+Following this, we implement the division algorithm by repeated shift-subtract.
+
+References:
+- Fast 32-bit Division on the DSP56800E: Minimized nonrestoring division algorithm by David Baca
+- Bitwuzla sources for bitblasting.h
+-/
+
+private theorem Nat.div_add_eq_left_of_lt {x y z : Nat} (hx : z ∣ x) (hy : y < z) (hz : 0 < z) :
+    (x + y) / z = x / z := by
+  refine Nat.div_eq_of_lt_le ?lo ?hi
+  · apply Nat.le_trans
+    · exact div_mul_le_self x z
+    · omega
+  · simp only [succ_eq_add_one, Nat.add_mul, Nat.one_mul]
+    apply Nat.add_lt_add_of_le_of_lt
+    · apply Nat.le_of_eq
+      exact (Nat.div_eq_iff_eq_mul_left hz hx).mp rfl
+    · exact hy
+
+/-- If the division equation `d.toNat * q.toNat + r.toNat = n.toNat` holds,
+then `n.udiv d = q`. -/
+theorem udiv_eq_of_mul_add_toNat {d n q r : BitVec w} (hd : 0 < d)
+    (hrd : r < d)
+    (hdqnr : d.toNat * q.toNat + r.toNat = n.toNat) :
+    n / d = q := by
+  apply BitVec.eq_of_toNat_eq
+  rw [toNat_udiv]
+  replace hdqnr : (d.toNat * q.toNat + r.toNat) / d.toNat = n.toNat / d.toNat := by
+    simp [hdqnr]
+  rw [Nat.div_add_eq_left_of_lt] at hdqnr
+  · rw [← hdqnr]
+    exact mul_div_right q.toNat hd
+  · exact Nat.dvd_mul_right d.toNat q.toNat
+  · exact hrd
+  · exact hd
+
+/-- If the division equation `d.toNat * q.toNat + r.toNat = n.toNat` holds,
+then `n.umod d = r`. -/
+theorem umod_eq_of_mul_add_toNat {d n q r : BitVec w} (hrd : r < d)
+    (hdqnr : d.toNat * q.toNat + r.toNat = n.toNat) :
+    n % d = r := by
+  apply BitVec.eq_of_toNat_eq
+  rw [toNat_umod]
+  replace hdqnr : (d.toNat * q.toNat + r.toNat) % d.toNat = n.toNat % d.toNat := by
+    simp [hdqnr]
+  rw [Nat.add_mod, Nat.mul_mod_right] at hdqnr
+  simp only [Nat.zero_add, mod_mod] at hdqnr
+  replace hrd : r.toNat < d.toNat := by
+    simpa [BitVec.lt_def] using hrd
+  rw [Nat.mod_eq_of_lt hrd] at hdqnr
+  simp [hdqnr]
+
+/-! ### DivModState -/
+
+/-- `DivModState` is a structure that maintains the state of recursive `divrem` calls. -/
+structure DivModState (w : Nat) : Type where
+  /-- The number of bits in the numerator that are not yet processed -/
+  wn : Nat
+  /-- The number of bits in the remainder (and quotient) -/
+  wr : Nat
+  /-- The current quotient. -/
+  q : BitVec w
+  /-- The current remainder. -/
+  r : BitVec w
+
+
+/-- `DivModArgs` contains the arguments to a `divrem` call which remain constant throughout
+execution. -/
+structure DivModArgs (w : Nat) where
+  /-- the numerator (aka, dividend) -/
+  n : BitVec w
+  /-- the denumerator (aka, divisor)-/
+  d : BitVec w
+
+/-- A `DivModState` is lawful if the remainder width `wr` plus the numerator width `wn` equals `w`,
+and the bitvectors `r` and `n` have values in the bounds given by bitwidths `wr`, resp. `wn`.
+
+This is a proof engineering choice: an alternative world could have been
+`r : BitVec wr` and `n : BitVec wn`, but this required much more dependent typing coercions.
+
+Instead, we choose to declare all involved bitvectors as length `w`, and then prove that
+the values are within their respective bounds.
+
+We start with `wn = w` and `wr = 0`, and then in each step, we decrement `wn` and increment `wr`.
+In this way, we grow a legal remainder in each loop iteration.
+-/
+structure DivModState.Lawful {w : Nat} (args : DivModArgs w) (qr : DivModState w) : Prop where
+  /-- The sum of widths of the dividend and remainder is `w`. -/
+  hwrn : qr.wr + qr.wn = w
+  /-- The denominator is positive. -/
+  hdPos : 0 < args.d
+  /-- The remainder is strictly less than the denominator. -/
+  hrLtDivisor : qr.r.toNat < args.d.toNat
+  /-- The remainder is morally a `Bitvec wr`, and so has value less than `2^wr`. -/
+  hrWidth : qr.r.toNat < 2^qr.wr
+  /-- The quotient is morally a `Bitvec wr`, and so has value less than `2^wr`. -/
+  hqWidth : qr.q.toNat < 2^qr.wr
+  /-- The low `(w - wn)` bits of `n` obey the invariant for division. -/
+  hdiv : args.n.toNat >>> qr.wn = args.d.toNat * qr.q.toNat + qr.r.toNat
+
+/-- A lawful DivModState implies `w > 0`. -/
+def DivModState.Lawful.hw {args : DivModArgs w} {qr : DivModState w}
+    {h : DivModState.Lawful args qr} : 0 < w := by
+  have hd := h.hdPos
+  rcases w with rfl | w
+  · have hcontra : args.d = 0#0 := by apply Subsingleton.elim
+    rw [hcontra] at hd
+    simp at hd
+  · omega
+
+/-- An initial value with both `q, r = 0`. -/
+def DivModState.init (w : Nat) : DivModState w := {
+  wn := w
+  wr := 0
+  q := 0#w
+  r := 0#w
+}
+
+/-- The initial state is lawful. -/
+def DivModState.lawful_init {w : Nat} (args : DivModArgs w) (hd : 0#w < args.d) :
+    DivModState.Lawful args (DivModState.init w) := by
+  simp only [BitVec.DivModState.init]
+  exact {
+    hwrn := by simp only; omega,
+    hdPos := by assumption
+    hrLtDivisor := by simp [BitVec.lt_def] at hd ⊢; assumption
+    hrWidth := by simp [DivModState.init],
+    hqWidth := by simp [DivModState.init],
+    hdiv := by
+      simp only [DivModState.init, toNat_ofNat, zero_mod, Nat.mul_zero, Nat.add_zero];
+      rw [Nat.shiftRight_eq_div_pow]
+      apply Nat.div_eq_of_lt args.n.isLt
+  }
+
+/--
+A lawful DivModState with a fully consumed dividend (`wn = 0`) witnesses that the
+quotient has been correctly computed.
+-/
+theorem DivModState.udiv_eq_of_lawful {n d : BitVec w} {qr : DivModState w}
+    (h_lawful : DivModState.Lawful {n, d} qr)
+    (h_final  : qr.wn = 0) :
+    n / d = qr.q := by
+  apply udiv_eq_of_mul_add_toNat h_lawful.hdPos h_lawful.hrLtDivisor
+  have hdiv := h_lawful.hdiv
+  simp only [h_final] at *
+  omega
+
+/--
+A lawful DivModState with a fully consumed dividend (`wn = 0`) witnesses that the
+remainder has been correctly computed.
+-/
+theorem DivModState.umod_eq_of_lawful {qr : DivModState w}
+    (h : DivModState.Lawful {n, d} qr)
+    (h_final  : qr.wn = 0) :
+    n % d = qr.r := by
+  apply umod_eq_of_mul_add_toNat h.hrLtDivisor
+  have hdiv := h.hdiv
+  simp only [shiftRight_zero] at hdiv
+  simp only [h_final] at *
+  exact hdiv.symm
+
+/-! ### DivModState.Poised -/
+
+/--
+A `Poised` DivModState is a state which is `Lawful` and furthermore, has at least
+one numerator bit left to process `(0 < wn)`
+
+The input to the shift subtractor is a legal input to `divrem`, and we also need to have an
+input bit to perform shift subtraction on, and thus we need `0 < wn`.
+-/
+structure DivModState.Poised {w : Nat} (args : DivModArgs w) (qr : DivModState w)
+  extends DivModState.Lawful args qr : Type where
+  /-- Only perform a round of shift-subtract if we have dividend bits. -/
+  hwn_lt : 0 < qr.wn
+
+/--
+In the shift subtract input, the dividend is at least one bit long (`wn > 0`), so
+the remainder has bits to be computed (`wr < w`).
+-/
+def DivModState.wr_lt_w {qr : DivModState w} (h : qr.Poised args) : qr.wr < w := by
+  have hwrn := h.hwrn
+  have hwn_lt := h.hwn_lt
+  omega
+
+/-! ### Division shift subtractor -/
+
+/--
+One round of the division algorithm, that tries to perform a subtract shift.
+Note that this should only be called when `r.msb = false`, so we will not overflow.
+-/
+def divSubtractShift (args : DivModArgs w) (qr : DivModState w) : DivModState w :=
+  let {n, d} := args
+  let wn := qr.wn - 1
+  let wr := qr.wr + 1
+  let r' := shiftConcat qr.r (n.getLsbD wn)
+  if r' < d then {
+    q := qr.q.shiftConcat false, -- If `r' < d`, then we do not have a quotient bit.
+    r := r'
+    wn, wr
+  } else {
+    q := qr.q.shiftConcat true, -- Otherwise, `r' ≥ d`, and we have a quotient bit.
+    r := r' - d -- we subtract to maintain the invariant that `r < d`.
+    wn, wr
+  }
+
+/-- The value of shifting right by `wn - 1` equals shifting by `wn` and grabbing the lsb at `(wn - 1)`. -/
+theorem DivModState.toNat_shiftRight_sub_one_eq
+    {args : DivModArgs w} {qr : DivModState w} (h : qr.Poised args) :
+    args.n.toNat >>> (qr.wn - 1)
+    = (args.n.toNat >>> qr.wn) * 2 + (args.n.getLsbD (qr.wn - 1)).toNat := by
+  show BitVec.toNat (args.n >>> (qr.wn - 1)) = _
+  have {..} := h -- break the structure down for `omega`
+  rw [shiftRight_sub_one_eq_shiftConcat args.n h.hwn_lt]
+  rw [toNat_shiftConcat_eq_of_lt (k := w - qr.wn)]
+  · simp
+  · omega
+  · apply BitVec.toNat_ushiftRight_lt
+    omega
+
+/--
+This is used when proving the correctness of the division algorithm,
+where we know that `r < d`.
+We then want to show that `((r.shiftConcat b) - d) < d` as the loop invariant.
+In arithmetic, this is the same as showing that
+`r * 2 + 1 - d < d`, which this theorem establishes.
+-/
+private theorem two_mul_add_sub_lt_of_lt_of_lt_two (h : a < x) (hy : y < 2) :
+    2 * a + y - x < x := by omega
+
+/-- We show that the output of `divSubtractShift` is lawful, which tells us that it
+obeys the division equation. -/
+theorem lawful_divSubtractShift (qr : DivModState w) (h : qr.Poised args) :
+    DivModState.Lawful args (divSubtractShift args qr) := by
+  rcases args with ⟨n, d⟩
+  simp only [divSubtractShift, decide_eq_true_eq]
+  -- We add these hypotheses for `omega` to find them later.
+  have ⟨⟨hrwn, hd, hrd, hr, hn, hrnd⟩, hwn_lt⟩ := h
+  have : d.toNat * (qr.q.toNat * 2) = d.toNat * qr.q.toNat * 2 := by rw [Nat.mul_assoc]
+  by_cases rltd : shiftConcat qr.r (n.getLsbD (qr.wn - 1)) < d
+  · simp only [rltd, ↓reduceIte]
+    constructor <;> try bv_omega
+    case pos.hrWidth => apply toNat_shiftConcat_lt_of_lt <;> omega
+    case pos.hqWidth => apply toNat_shiftConcat_lt_of_lt <;> omega
+    case pos.hdiv =>
+      simp [qr.toNat_shiftRight_sub_one_eq h, h.hdiv, this,
+        toNat_shiftConcat_eq_of_lt (qr.wr_lt_w h) h.hrWidth,
+        toNat_shiftConcat_eq_of_lt (qr.wr_lt_w h) h.hqWidth]
+      omega
+  · simp only [rltd, ↓reduceIte]
+    constructor <;> try bv_omega
+    case neg.hrLtDivisor =>
+      simp only [lt_def, Nat.not_lt] at rltd
+      rw [BitVec.toNat_sub_of_le rltd,
+        toNat_shiftConcat_eq_of_lt (hk := qr.wr_lt_w h) (hx := h.hrWidth),
+        Nat.mul_comm]
+      apply two_mul_add_sub_lt_of_lt_of_lt_two <;> bv_omega
+    case neg.hrWidth =>
+      simp only
+      have hdr' : d ≤ (qr.r.shiftConcat (n.getLsbD (qr.wn - 1))) :=
+        BitVec.not_lt_iff_le.mp rltd
+      have hr' : ((qr.r.shiftConcat (n.getLsbD (qr.wn - 1)))).toNat < 2 ^ (qr.wr + 1) := by
+        apply toNat_shiftConcat_lt_of_lt <;> bv_omega
+      rw [BitVec.toNat_sub_of_le hdr']
+      omega
+    case neg.hqWidth =>
+      apply toNat_shiftConcat_lt_of_lt <;> omega
+    case neg.hdiv =>
+      have rltd' := (BitVec.not_lt_iff_le.mp rltd)
+      simp only [qr.toNat_shiftRight_sub_one_eq h,
+        BitVec.toNat_sub_of_le rltd',
+        toNat_shiftConcat_eq_of_lt (qr.wr_lt_w h) h.hrWidth]
+      simp only [BitVec.le_def,
+        toNat_shiftConcat_eq_of_lt (qr.wr_lt_w h) h.hrWidth] at rltd'
+      simp only [toNat_shiftConcat_eq_of_lt (qr.wr_lt_w h) h.hqWidth, h.hdiv, Nat.mul_add]
+      bv_omega
+
+/-! ### Core division algorithm circuit -/
+
+/-- A recursive definition of division for bitblasting, in terms of a shift-subtraction circuit. -/
+def divRec {w : Nat} (m : Nat) (args : DivModArgs w) (qr : DivModState w) :
+    DivModState w :=
+  match m with
+  | 0 => qr
+  | m + 1 => divRec m args <| divSubtractShift args qr
+
+@[simp]
+theorem divRec_zero (qr : DivModState w) :
+    divRec 0 args qr = qr := rfl
+
+@[simp]
+theorem divRec_succ (m : Nat) (args : DivModArgs w) (qr : DivModState w) :
+    divRec (m + 1) args qr =
+      divRec m args (divSubtractShift args qr) := rfl
+
+/-- The output of `divRec` is a lawful state -/
+theorem lawful_divRec {args : DivModArgs w} {qr : DivModState w}
+    (h : DivModState.Lawful args qr) :
+    DivModState.Lawful args (divRec qr.wn args qr) := by
+  generalize hm : qr.wn = m
+  induction m generalizing qr
+  case zero =>
+    exact h
+  case succ wn' ih =>
+    simp only [divRec_succ]
+    apply ih
+    · apply lawful_divSubtractShift
+      constructor
+      · assumption
+      · omega
+    · simp only [divSubtractShift, hm]
+      split <;> rfl
+
+/-- The output of `divRec` has no more bits left to process (i.e., `wn = 0`) -/
+@[simp]
+theorem wn_divRec (args : DivModArgs w) (qr : DivModState w) :
+    (divRec qr.wn args qr).wn = 0 := by
+  generalize hm : qr.wn = m
+  induction m generalizing qr
+  case zero =>
+    assumption
+  case succ wn' ih =>
+    apply ih
+    simp only [divSubtractShift, hm]
+    split <;> rfl
+
+/-- The result of `udiv` agrees with the result of the division recurrence. -/
+theorem udiv_eq_divRec (hd : 0#w < d) :
+    let out := divRec w {n, d} (DivModState.init w)
+    n / d = out.q := by
+  have := DivModState.lawful_init {n, d} hd
+  have := lawful_divRec this
+  apply DivModState.udiv_eq_of_lawful this (wn_divRec ..)
+
+/-- The result of `umod` agrees with the result of the division recurrence. -/
+theorem umod_eq_divRec (hd : 0#w < d) :
+    let out := divRec w {n, d} (DivModState.init w)
+    n % d = out.r := by
+  have := DivModState.lawful_init {n, d} hd
+  have := lawful_divRec this
+  apply DivModState.umod_eq_of_lawful this (wn_divRec ..)
+
+theorem divRec_succ' (m : Nat) (args : DivModArgs w) (qr : DivModState w) :
+    divRec (m+1) args qr =
+    let wn := qr.wn - 1
+    let wr := qr.wr + 1
+    let r' := shiftConcat qr.r (args.n.getLsbD wn)
+    let input : DivModState _ :=
+      if r' < args.d then {
+        q := qr.q.shiftConcat false,
+        r := r'
+        wn, wr
+      } else {
+        q := qr.q.shiftConcat true,
+        r := r' - args.d
+        wn, wr
+      }
+    divRec m args input := by
+  simp [divRec_succ, divSubtractShift]
+
 /- ### Arithmetic shift right (sshiftRight) recurrence -/
 
 /--
@@ -454,8 +1092,8 @@ def sshiftRightRec (x : BitVec w₁) (y : BitVec w₂) (n : Nat) : BitVec w₁ :
 
 @[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]
+    sshiftRightRec x y 0 = x.sshiftRight' (y &&& twoPow w₂ 0) := by
+  simp only [sshiftRightRec]
 
 @[simp]
 theorem sshiftRightRec_succ_eq (x : BitVec w₁) (y : BitVec w₂) (n : Nat) :

src/Init/Data/BitVec/Folds.lean

@@ -65,7 +65,7 @@ theorem iunfoldr_getLsbD' {f : Fin w → α → α × Bool} (state : Nat → α)
     intro
     apply And.intro
     · intro i
-      have := Fin.size_pos i
+      have := Fin.pos i
       contradiction
     · rfl
   case step =>

src/Init/Data/Bool.lean

@@ -368,13 +368,14 @@ theorem and_or_inj_left_iff :
 /-- convert a `Bool` to a `Nat`, `false -> 0`, `true -> 1` -/
 def toNat (b : Bool) : Nat := cond b 1 0
 
-@[simp] theorem toNat_false : false.toNat = 0 := rfl
+@[simp, bv_toNat] theorem toNat_false : false.toNat = 0 := rfl
 
-@[simp] theorem toNat_true : true.toNat = 1 := rfl
+@[simp, bv_toNat] theorem toNat_true : true.toNat = 1 := rfl
 
 theorem toNat_le (c : Bool) : c.toNat ≤ 1 := by
   cases c <;> trivial
 
+@[bv_toNat]
 theorem toNat_lt (b : Bool) : b.toNat < 2 :=
   Nat.lt_succ_of_le (toNat_le _)
 

src/Init/Data/ByteArray/Basic.lean

@@ -42,7 +42,7 @@ def usize (a : @& ByteArray) : USize :=
   a.size.toUSize
 
 @[extern "lean_byte_array_uget"]
-def uget : (a : @& ByteArray) → (i : USize) → i.toNat < a.size → UInt8
+def uget : (a : @& ByteArray) → (i : USize) → (h : i.toNat < a.size := by get_elem_tactic) → UInt8
   | ⟨bs⟩, i, h => bs[i]
 
 @[extern "lean_byte_array_get"]
@@ -50,11 +50,11 @@ def get! : (@& ByteArray) → (@& Nat) → UInt8
   | ⟨bs⟩, i => bs.get! i
 
 @[extern "lean_byte_array_fget"]
-def get : (a : @& ByteArray) → (@& Fin a.size) → UInt8
-  | ⟨bs⟩, i => bs.get i
+def get : (a : @& ByteArray) → (i : @& Nat) → (h : i < a.size := by get_elem_tactic) → UInt8
+  | ⟨bs⟩, i, _ => bs[i]
 
 instance : GetElem ByteArray Nat UInt8 fun xs i => i < xs.size where
-  getElem xs i h := xs.get ⟨i, h⟩
+  getElem xs i h := xs.get i
 
 instance : GetElem ByteArray USize UInt8 fun xs i => i.val < xs.size where
   getElem xs i h := xs.uget i h
@@ -64,11 +64,11 @@ def set! : ByteArray → (@& Nat) → UInt8 → ByteArray
   | ⟨bs⟩, i, b => ⟨bs.set! i b⟩
 
 @[extern "lean_byte_array_fset"]
-def set : (a : ByteArray) → (@& Fin a.size) → UInt8 → ByteArray
-  | ⟨bs⟩, i, b => ⟨bs.set i b⟩
+def set : (a : ByteArray) → (i : @& Nat) → UInt8 → (h : i < a.size := by get_elem_tactic) → ByteArray
+  | ⟨bs⟩, i, b, h => ⟨bs.set i b h⟩
 
 @[extern "lean_byte_array_uset"]
-def uset : (a : ByteArray) → (i : USize) → UInt8 → i.toNat < a.size → ByteArray
+def uset : (a : ByteArray) → (i : USize) → UInt8 → (h : i.toNat < a.size := by get_elem_tactic) → ByteArray
   | ⟨bs⟩, i, v, h => ⟨bs.uset i v h⟩
 
 @[extern "lean_byte_array_hash"]
@@ -144,7 +144,7 @@ protected def forIn {β : Type v} {m : Type v → Type w} [Monad m] (as : ByteAr
       have h' : i < as.size            := Nat.lt_of_lt_of_le (Nat.lt_succ_self i) h
       have : as.size - 1 < as.size     := Nat.sub_lt (Nat.zero_lt_of_lt h') (by decide)
       have : as.size - 1 - i < as.size := Nat.lt_of_le_of_lt (Nat.sub_le (as.size - 1) i) this
-      match (← f (as.get ⟨as.size - 1 - i, this⟩) b) with
+      match (← f as[as.size - 1 - i] b) with
       | ForInStep.done b  => pure b
       | ForInStep.yield b => loop i (Nat.le_of_lt h') b
   loop as.size (Nat.le_refl _) b
@@ -178,7 +178,7 @@ def foldlM {β : Type v} {m : Type v → Type w} [Monad m] (f : β → UInt8 →
         match i with
         | 0    => pure b
         | i'+1 =>
-          loop i' (j+1) (← f b (as.get ⟨j, Nat.lt_of_lt_of_le hlt h⟩))
+          loop i' (j+1) (← f b as[j])
       else
         pure b
     loop (stop - start) start init
@@ -245,7 +245,7 @@ On an invalid position, returns `(default : UInt8)`. -/
 @[inline]
 def curr : Iterator → UInt8
   | ⟨arr, i⟩ =>
-    if h:i < arr.size then
+    if h : i < arr.size then
       arr[i]'h
     else
       default

src/Init/Data/Char/Basic.lean

@@ -4,7 +4,7 @@ Released under Apache 2.0 license as described in the file LICENSE.
 Author: Leonardo de Moura
 -/
 prelude
-import Init.Data.UInt.Basic
+import Init.Data.UInt.BasicAux
 
 /-- Determines if the given integer is a valid [Unicode scalar value](https://www.unicode.org/glossary/#unicode_scalar_value).
 
@@ -42,8 +42,10 @@ theorem isValidUInt32 (n : Nat) (h : isValidCharNat n) : n < UInt32.size := by
 
 theorem isValidChar_of_isValidCharNat (n : Nat) (h : isValidCharNat n) : isValidChar (UInt32.ofNat' n (isValidUInt32 n h)) :=
   match h with
-  | Or.inl h        => Or.inl h
-  | Or.inr ⟨h₁, h₂⟩ => Or.inr ⟨h₁, h₂⟩
+  | Or.inl h =>
+    Or.inl (UInt32.ofNat'_lt_of_lt _ (by decide) h)
+  | Or.inr ⟨h₁, h₂⟩ =>
+    Or.inr ⟨UInt32.lt_ofNat'_of_lt _ (by decide) h₁, UInt32.ofNat'_lt_of_lt _ (by decide) h₂⟩
 
 theorem isValidChar_zero : isValidChar 0 :=
   Or.inl (by decide)
@@ -57,7 +59,7 @@ theorem isValidChar_zero : isValidChar 0 :=
   c.val.toUInt8
 
 /-- The numbers from 0 to 256 are all valid UTF-8 characters, so we can embed one in the other. -/
-def ofUInt8 (n : UInt8) : Char := ⟨n.toUInt32, .inl (Nat.lt_trans n.1.2 (by decide))⟩
+def ofUInt8 (n : UInt8) : Char := ⟨n.toUInt32, .inl (Nat.lt_trans n.toBitVec.isLt (by decide))⟩
 
 instance : Inhabited Char where
   default := 'A'

src/Init/Data/Fin/Basic.lean

@@ -165,6 +165,7 @@ theorem modn_lt : ∀ {m : Nat} (i : Fin n), m > 0 → (modn i m).val < m
 theorem val_lt_of_le (i : Fin b) (h : b ≤ n) : i.val < n :=
   Nat.lt_of_lt_of_le i.isLt h
 
+/-- If you actually have an element of `Fin n`, then the `n` is always positive -/
 protected theorem pos (i : Fin n) : 0 < n :=
   Nat.lt_of_le_of_lt (Nat.zero_le _) i.2
 

src/Init/Data/Fin/Fold.lean

@@ -5,6 +5,8 @@ Authors: François G. Dorais
 -/
 prelude
 import Init.Data.Nat.Linear
+import Init.Control.Lawful.Basic
+import Init.Data.Fin.Lemmas
 
 namespace Fin
 
@@ -23,4 +25,195 @@ namespace Fin
   | ⟨0, _⟩, x => x
   | ⟨i+1, h⟩, x => loop ⟨i, Nat.le_of_lt h⟩ (f ⟨i, h⟩ x)
 
+/--
+Folds a monadic function over `Fin n` from left to right:
+```
+Fin.foldlM n f x₀ = do
+  let x₁ ← f x₀ 0
+  let x₂ ← f x₁ 1
+  ...
+  let xₙ ← f xₙ₋₁ (n-1)
+  pure xₙ
+```
+-/
+@[inline] def foldlM [Monad m] (n) (f : α → Fin n → m α) (init : α) : m α := loop init 0 where
+  /--
+  Inner loop for `Fin.foldlM`.
+  ```
+  Fin.foldlM.loop n f xᵢ i = do
+    let xᵢ₊₁ ← f xᵢ i
+    ...
+    let xₙ ← f xₙ₋₁ (n-1)
+    pure xₙ
+  ```
+  -/
+  loop (x : α) (i : Nat) : m α := do
+    if h : i < n then f x ⟨i, h⟩ >>= (loop · (i+1)) else pure x
+  termination_by n - i
+  decreasing_by decreasing_trivial_pre_omega
+
+/--
+Folds a monadic function over `Fin n` from right to left:
+```
+Fin.foldrM n f xₙ = do
+  let xₙ₋₁ ← f (n-1) xₙ
+  let xₙ₋₂ ← f (n-2) xₙ₋₁
+  ...
+  let x₀ ← f 0 x₁
+  pure x₀
+```
+-/
+@[inline] def foldrM [Monad m] (n) (f : Fin n → α → m α) (init : α) : m α :=
+  loop ⟨n, Nat.le_refl n⟩ init where
+  /--
+  Inner loop for `Fin.foldrM`.
+  ```
+  Fin.foldrM.loop n f i xᵢ = do
+    let xᵢ₋₁ ← f (i-1) xᵢ
+    ...
+    let x₁ ← f 1 x₂
+    let x₀ ← f 0 x₁
+    pure x₀
+  ```
+  -/
+  loop : {i // i ≤ n} → α → m α
+  | ⟨0, _⟩, x => pure x
+  | ⟨i+1, h⟩, x => f ⟨i, h⟩ x >>= loop ⟨i, Nat.le_of_lt h⟩
+
+/-! ### foldlM -/
+
+theorem foldlM_loop_lt [Monad m] (f : α → Fin n → m α) (x) (h : i < n) :
+    foldlM.loop n f x i = f x ⟨i, h⟩ >>= (foldlM.loop n f . (i+1)) := by
+  rw [foldlM.loop, dif_pos h]
+
+theorem foldlM_loop_eq [Monad m] (f : α → Fin n → m α) (x) : foldlM.loop n f x n = pure x := by
+  rw [foldlM.loop, dif_neg (Nat.lt_irrefl _)]
+
+theorem foldlM_loop [Monad m] (f : α → Fin (n+1) → m α) (x) (h : i < n+1) :
+    foldlM.loop (n+1) f x i = f x ⟨i, h⟩ >>= (foldlM.loop n (fun x j => f x j.succ) . i) := by
+  if h' : i < n then
+    rw [foldlM_loop_lt _ _ h]
+    congr; funext
+    rw [foldlM_loop_lt _ _ h', foldlM_loop]; rfl
+  else
+    cases Nat.le_antisymm (Nat.le_of_lt_succ h) (Nat.not_lt.1 h')
+    rw [foldlM_loop_lt]
+    congr; funext
+    rw [foldlM_loop_eq, foldlM_loop_eq]
+termination_by n - i
+
+@[simp] theorem foldlM_zero [Monad m] (f : α → Fin 0 → m α) (x) : foldlM 0 f x = pure x :=
+  foldlM_loop_eq ..
+
+theorem foldlM_succ [Monad m] (f : α → Fin (n+1) → m α) (x) :
+    foldlM (n+1) f x = f x 0 >>= foldlM n (fun x j => f x j.succ) := foldlM_loop ..
+
+/-! ### foldrM -/
+
+theorem foldrM_loop_zero [Monad m] (f : Fin n → α → m α) (x) :
+    foldrM.loop n f ⟨0, Nat.zero_le _⟩ x = pure x := by
+  rw [foldrM.loop]
+
+theorem foldrM_loop_succ [Monad m] (f : Fin n → α → m α) (x) (h : i < n) :
+    foldrM.loop n f ⟨i+1, h⟩ x = f ⟨i, h⟩ x >>= foldrM.loop n f ⟨i, Nat.le_of_lt h⟩ := by
+  rw [foldrM.loop]
+
+theorem foldrM_loop [Monad m] [LawfulMonad m] (f : Fin (n+1) → α → m α) (x) (h : i+1 ≤ n+1) :
+    foldrM.loop (n+1) f ⟨i+1, h⟩ x =
+      foldrM.loop n (fun j => f j.succ) ⟨i, Nat.le_of_succ_le_succ h⟩ x >>= f 0 := by
+  induction i generalizing x with
+  | zero =>
+    rw [foldrM_loop_zero, foldrM_loop_succ, pure_bind]
+    conv => rhs; rw [←bind_pure (f 0 x)]
+    congr; funext; exact foldrM_loop_zero ..
+  | succ i ih =>
+    rw [foldrM_loop_succ, foldrM_loop_succ, bind_assoc]
+    congr; funext; exact ih ..
+
+@[simp] theorem foldrM_zero [Monad m] (f : Fin 0 → α → m α) (x) : foldrM 0 f x = pure x :=
+  foldrM_loop_zero ..
+
+theorem foldrM_succ [Monad m] [LawfulMonad m] (f : Fin (n+1) → α → m α) (x) :
+    foldrM (n+1) f x = foldrM n (fun i => f i.succ) x >>= f 0 := foldrM_loop ..
+
+/-! ### foldl -/
+
+theorem foldl_loop_lt (f : α → Fin n → α) (x) (h : i < n) :
+    foldl.loop n f x i = foldl.loop n f (f x ⟨i, h⟩) (i+1) := by
+  rw [foldl.loop, dif_pos h]
+
+theorem foldl_loop_eq (f : α → Fin n → α) (x) : foldl.loop n f x n = x := by
+  rw [foldl.loop, dif_neg (Nat.lt_irrefl _)]
+
+theorem foldl_loop (f : α → Fin (n+1) → α) (x) (h : i < n+1) :
+    foldl.loop (n+1) f x i = foldl.loop n (fun x j => f x j.succ) (f x ⟨i, h⟩) i := by
+  if h' : i < n then
+    rw [foldl_loop_lt _ _ h]
+    rw [foldl_loop_lt _ _ h', foldl_loop]; rfl
+  else
+    cases Nat.le_antisymm (Nat.le_of_lt_succ h) (Nat.not_lt.1 h')
+    rw [foldl_loop_lt]
+    rw [foldl_loop_eq, foldl_loop_eq]
+
+@[simp] theorem foldl_zero (f : α → Fin 0 → α) (x) : foldl 0 f x = x :=
+  foldl_loop_eq ..
+
+theorem foldl_succ (f : α → Fin (n+1) → α) (x) :
+    foldl (n+1) f x = foldl n (fun x i => f x i.succ) (f x 0) :=
+  foldl_loop ..
+
+theorem foldl_succ_last (f : α → Fin (n+1) → α) (x) :
+    foldl (n+1) f x = f (foldl n (f · ·.castSucc) x) (last n) := by
+  rw [foldl_succ]
+  induction n generalizing x with
+  | zero => simp [foldl_succ, Fin.last]
+  | succ n ih => rw [foldl_succ, ih (f · ·.succ), foldl_succ]; simp [succ_castSucc]
+
+theorem foldl_eq_foldlM (f : α → Fin n → α) (x) :
+    foldl n f x = foldlM (m:=Id) n f x := by
+  induction n generalizing x <;> simp [foldl_succ, foldlM_succ, *]
+
+/-! ### foldr -/
+
+theorem foldr_loop_zero (f : Fin n → α → α) (x) :
+    foldr.loop n f ⟨0, Nat.zero_le _⟩ x = x := by
+  rw [foldr.loop]
+
+theorem foldr_loop_succ (f : Fin n → α → α) (x) (h : i < n) :
+    foldr.loop n f ⟨i+1, h⟩ x = foldr.loop n f ⟨i, Nat.le_of_lt h⟩ (f ⟨i, h⟩ x) := by
+  rw [foldr.loop]
+
+theorem foldr_loop (f : Fin (n+1) → α → α) (x) (h : i+1 ≤ n+1) :
+    foldr.loop (n+1) f ⟨i+1, h⟩ x =
+      f 0 (foldr.loop n (fun j => f j.succ) ⟨i, Nat.le_of_succ_le_succ h⟩ x) := by
+  induction i generalizing x <;> simp [foldr_loop_zero, foldr_loop_succ, *]
+
+@[simp] theorem foldr_zero (f : Fin 0 → α → α) (x) : foldr 0 f x = x :=
+  foldr_loop_zero ..
+
+theorem foldr_succ (f : Fin (n+1) → α → α) (x) :
+    foldr (n+1) f x = f 0 (foldr n (fun i => f i.succ) x) := foldr_loop ..
+
+theorem foldr_succ_last (f : Fin (n+1) → α → α) (x) :
+    foldr (n+1) f x = foldr n (f ·.castSucc) (f (last n) x) := by
+  induction n generalizing x with
+  | zero => simp [foldr_succ, Fin.last]
+  | succ n ih => rw [foldr_succ, ih (f ·.succ), foldr_succ]; simp [succ_castSucc]
+
+theorem foldr_eq_foldrM (f : Fin n → α → α) (x) :
+    foldr n f x = foldrM (m:=Id) n f x := by
+  induction n <;> simp [foldr_succ, foldrM_succ, *]
+
+theorem foldl_rev (f : Fin n → α → α) (x) :
+    foldl n (fun x i => f i.rev x) x = foldr n f x := by
+  induction n generalizing x with
+  | zero => simp
+  | succ n ih => rw [foldl_succ, foldr_succ_last, ← ih]; simp [rev_succ]
+
+theorem foldr_rev (f : α → Fin n → α) (x) :
+     foldr n (fun i x => f x i.rev) x = foldl n f x := by
+  induction n generalizing x with
+  | zero => simp
+  | succ n ih => rw [foldl_succ_last, foldr_succ, ← ih]; simp [rev_succ]
+
 end Fin

src/Init/Data/Fin/Lemmas.lean

@@ -13,17 +13,19 @@ import Init.Omega
 
 namespace Fin
 
-/-- If you actually have an element of `Fin n`, then the `n` is always positive -/
-theorem size_pos (i : Fin n) : 0 < n := Nat.lt_of_le_of_lt (Nat.zero_le _) i.2
+@[deprecated Fin.pos (since := "2024-11-11")]
+theorem size_pos (i : Fin n) : 0 < n := i.pos
 
 theorem mod_def (a m : Fin n) : a % m = Fin.mk (a % m) (Nat.lt_of_le_of_lt (Nat.mod_le _ _) a.2) :=
   rfl
 
-theorem mul_def (a b : Fin n) : a * b = Fin.mk ((a * b) % n) (Nat.mod_lt _ a.size_pos) := rfl
+theorem mul_def (a b : Fin n) : a * b = Fin.mk ((a * b) % n) (Nat.mod_lt _ a.pos) := rfl
 
-theorem sub_def (a b : Fin n) : a - b = Fin.mk (((n - b) + a) % n) (Nat.mod_lt _ a.size_pos) := rfl
+theorem sub_def (a b : Fin n) : a - b = Fin.mk (((n - b) + a) % n) (Nat.mod_lt _ a.pos) := rfl
 
-theorem size_pos' : ∀ [Nonempty (Fin n)], 0 < n | ⟨i⟩ => i.size_pos
+theorem pos' : ∀ [Nonempty (Fin n)], 0 < n | ⟨i⟩ => i.pos
+
+@[deprecated pos' (since := "2024-11-11")] abbrev size_pos' := @pos'
 
 @[simp] theorem is_lt (a : Fin n) : (a : Nat) < n := a.2
 
@@ -240,13 +242,17 @@ theorem fin_one_eq_zero (a : Fin 1) : a = 0 := Subsingleton.elim a 0
   rw [eq_comm]
   simp
 
-theorem add_def (a b : Fin n) : a + b = Fin.mk ((a + b) % n) (Nat.mod_lt _ a.size_pos) := rfl
+theorem add_def (a b : Fin n) : a + b = Fin.mk ((a + b) % n) (Nat.mod_lt _ a.pos) := rfl
 
 theorem val_add (a b : Fin n) : (a + b).val = (a.val + b.val) % n := rfl
 
-@[simp] protected theorem zero_add {n : Nat} [NeZero n] (i : Fin n) : (0 : Fin n) + i = i := by
+@[simp] protected theorem zero_add [NeZero n] (k : Fin n) : (0 : Fin n) + k = k := by
   ext
-  simp [Fin.add_def, Nat.mod_eq_of_lt i.2]
+  simp [Fin.add_def, Nat.mod_eq_of_lt k.2]
+
+@[simp] protected theorem add_zero [NeZero n] (k : Fin n) : k + 0 = k := by
+  ext
+  simp [add_def, Nat.mod_eq_of_lt k.2]
 
 theorem val_add_one_of_lt {n : Nat} {i : Fin n.succ} (h : i < last _) : (i + 1).1 = i + 1 := by
   match n with
@@ -582,8 +588,8 @@ theorem rev_succ (k : Fin n) : rev (succ k) = castSucc (rev k) := k.rev_addNat 1
 @[simp] theorem coe_pred (j : Fin (n + 1)) (h : j ≠ 0) : (j.pred h : Nat) = j - 1 := rfl
 
 @[simp] theorem succ_pred : ∀ (i : Fin (n + 1)) (h : i ≠ 0), (i.pred h).succ = i
-  | ⟨0, h⟩, hi => by simp only [mk_zero, ne_eq, not_true] at hi
-  | ⟨n + 1, h⟩, hi => rfl
+  | ⟨0, _⟩, hi => by simp only [mk_zero, ne_eq, not_true] at hi
+  | ⟨_ + 1, _⟩, _ => rfl
 
 @[simp]
 theorem pred_succ (i : Fin n) {h : i.succ ≠ 0} : i.succ.pred h = i := by

src/Init/Data/Float.lean

@@ -72,21 +72,35 @@ instance floatDecLt (a b : Float) : Decidable (a < b) := Float.decLt a b
 instance floatDecLe (a b : Float) : Decidable (a ≤ b) := Float.decLe a b
 
 @[extern "lean_float_to_string"] opaque Float.toString : Float → String
-
-/-- If the given float is positive, truncates the value to the nearest positive integer.
-If negative or larger than the maximum value for UInt8, returns 0. -/
+/-- If the given float is non-negative, truncates the value to the nearest non-negative integer.
+If negative or NaN, returns `0`.
+If larger than the maximum value for `UInt8` (including Inf), returns the maximum value of `UInt8`
+(i.e. `UInt8.size - 1`).
+-/
 @[extern "lean_float_to_uint8"] opaque Float.toUInt8 : Float → UInt8
-/-- If the given float is positive, truncates the value to the nearest positive integer.
-If negative or larger than the maximum value for UInt16, returns 0. -/
+/-- If the given float is non-negative, truncates the value to the nearest non-negative integer.
+If negative or NaN, returns `0`.
+If larger than the maximum value for `UInt16` (including Inf), returns the maximum value of `UInt16`
+(i.e. `UInt16.size - 1`).
+-/
 @[extern "lean_float_to_uint16"] opaque Float.toUInt16 : Float → UInt16
-/-- If the given float is positive, truncates the value to the nearest positive integer.
-If negative or larger than the maximum value for UInt32, returns 0. -/
+/-- If the given float is non-negative, truncates the value to the nearest non-negative integer.
+If negative or NaN, returns `0`.
+If larger than the maximum value for `UInt32` (including Inf), returns the maximum value of `UInt32`
+(i.e. `UInt32.size - 1`).
+-/
 @[extern "lean_float_to_uint32"] opaque Float.toUInt32 : Float → UInt32
-/-- If the given float is positive, truncates the value to the nearest positive integer.
-If negative or larger than the maximum value for UInt64, returns 0. -/
+/-- If the given float is non-negative, truncates the value to the nearest non-negative integer.
+If negative or NaN, returns `0`.
+If larger than the maximum value for `UInt64` (including Inf), returns the maximum value of `UInt64`
+(i.e. `UInt64.size - 1`).
+-/
 @[extern "lean_float_to_uint64"] opaque Float.toUInt64 : Float → UInt64
-/-- If the given float is positive, truncates the value to the nearest positive integer.
-If negative or larger than the maximum value for USize, returns 0. -/
+/-- If the given float is non-negative, truncates the value to the nearest non-negative integer.
+If negative or NaN, returns `0`.
+If larger than the maximum value for `USize` (including Inf), returns the maximum value of `USize`
+(i.e. `USize.size - 1`). This value is platform dependent).
+-/
 @[extern "lean_float_to_usize"] opaque Float.toUSize : Float → USize
 
 @[extern "lean_float_isnan"] opaque Float.isNaN : Float → Bool

src/Init/Data/FloatArray/Basic.lean

@@ -46,8 +46,8 @@ def uget : (a : @& FloatArray) → (i : USize) → i.toNat < a.size → Float
   | ⟨ds⟩, i, h => ds[i]
 
 @[extern "lean_float_array_fget"]
-def get : (ds : @& FloatArray) → (@& Fin ds.size) → Float
-  | ⟨ds⟩, i => ds.get i
+def get : (ds : @& FloatArray) → (i : @& Nat) → (h : i < ds.size := by get_elem_tactic) → Float
+  | ⟨ds⟩, i, h => ds.get i h
 
 @[extern "lean_float_array_get"]
 def get! : (@& FloatArray) → (@& Nat) → Float
@@ -55,23 +55,23 @@ def get! : (@& FloatArray) → (@& Nat) → Float
 
 def get? (ds : FloatArray) (i : Nat) : Option Float :=
   if h : i < ds.size then
-    ds.get ⟨i, h⟩
+    some (ds.get i h)
   else
     none
 
 instance : GetElem FloatArray Nat Float fun xs i => i < xs.size where
-  getElem xs i h := xs.get ⟨i, h⟩
+  getElem xs i h := xs.get i h
 
 instance : GetElem FloatArray USize Float fun xs i => i.val < xs.size where
   getElem xs i h := xs.uget i h
 
 @[extern "lean_float_array_uset"]
-def uset : (a : FloatArray) → (i : USize) → Float → i.toNat < a.size → FloatArray
+def uset : (a : FloatArray) → (i : USize) → Float → (h : i.toNat < a.size := by get_elem_tactic) → FloatArray
   | ⟨ds⟩, i, v, h => ⟨ds.uset i v h⟩
 
 @[extern "lean_float_array_fset"]
-def set : (ds : FloatArray) → (@& Fin ds.size) → Float → FloatArray
-  | ⟨ds⟩, i, d => ⟨ds.set i d⟩
+def set : (ds : FloatArray) → (i : @& Nat) → Float → (h : i < ds.size := by get_elem_tactic) → FloatArray
+  | ⟨ds⟩, i, d, h => ⟨ds.set i d h⟩
 
 @[extern "lean_float_array_set"]
 def set! : FloatArray → (@& Nat) → Float → FloatArray
@@ -83,7 +83,7 @@ def isEmpty (s : FloatArray) : Bool :=
 partial def toList (ds : FloatArray) : List Float :=
   let rec loop (i r) :=
     if h : i < ds.size then
-      loop (i+1) (ds.get ⟨i, h⟩ :: r)
+      loop (i+1) (ds[i] :: r)
     else
       r.reverse
   loop 0 []
@@ -115,7 +115,7 @@ protected def forIn {β : Type v} {m : Type v → Type w} [Monad m] (as : FloatA
       have h' : i < as.size            := Nat.lt_of_lt_of_le (Nat.lt_succ_self i) h
       have : as.size - 1 < as.size     := Nat.sub_lt (Nat.zero_lt_of_lt h') (by decide)
       have : as.size - 1 - i < as.size := Nat.lt_of_le_of_lt (Nat.sub_le (as.size - 1) i) this
-      match (← f (as.get ⟨as.size - 1 - i, this⟩) b) with
+      match (← f as[as.size - 1 - i] b) with
       | ForInStep.done b  => pure b
       | ForInStep.yield b => loop i (Nat.le_of_lt h') b
   loop as.size (Nat.le_refl _) b
@@ -149,7 +149,7 @@ def foldlM {β : Type v} {m : Type v → Type w} [Monad m] (f : β → Float →
         match i with
         | 0    => pure b
         | i'+1 =>
-          loop i' (j+1) (← f b (as.get ⟨j, Nat.lt_of_lt_of_le hlt h⟩))
+          loop i' (j+1) (← f b (as[j]'(Nat.lt_of_lt_of_le hlt h)))
       else
         pure b
     loop (stop - start) start init

src/Init/Data/Function.lean

@@ -0,0 +1,35 @@
+/-
+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.Core
+
+namespace Function
+
+@[inline]
+def curry : (α × β → φ) → α → β → φ := fun f a b => f (a, b)
+
+/-- Interpret a function with two arguments as a function on `α × β` -/
+@[inline]
+def uncurry : (α → β → φ) → α × β → φ := fun f a => f a.1 a.2
+
+@[simp]
+theorem curry_uncurry (f : α → β → φ) : curry (uncurry f) = f :=
+  rfl
+
+@[simp]
+theorem uncurry_curry (f : α × β → φ) : uncurry (curry f) = f :=
+  funext fun ⟨_a, _b⟩ => rfl
+
+@[simp]
+theorem uncurry_apply_pair {α β γ} (f : α → β → γ) (x : α) (y : β) : uncurry f (x, y) = f x y :=
+  rfl
+
+@[simp]
+theorem curry_apply {α β γ} (f : α × β → γ) (x : α) (y : β) : curry f x y = f (x, y) :=
+  rfl
+
+end Function

src/Init/Data/Hashable.lean

@@ -48,9 +48,15 @@ instance : Hashable UInt64 where
 instance : Hashable USize where
   hash n := n.toUInt64
 
+instance : Hashable ByteArray where
+  hash as := as.foldl (fun r a => mixHash r (hash a)) 7
+
 instance : Hashable (Fin n) where
   hash v := v.val.toUInt64
 
+instance : Hashable Char where
+  hash c := c.val.toUInt64
+
 instance : Hashable Int where
   hash
     | Int.ofNat n => UInt64.ofNat (2 * n)

src/Init/Data/Int/DivModLemmas.lean

@@ -253,7 +253,7 @@ theorem tmod_def (a b : Int) : tmod a b = a - b * a.tdiv b := by
 
 theorem fmod_add_fdiv : ∀ a b : Int, a.fmod b + b * a.fdiv b = a
   | 0, ofNat _ | 0, -[_+1] => congrArg ofNat <| by simp
-  | succ m, ofNat n => congrArg ofNat <| Nat.mod_add_div ..
+  | succ _, ofNat _ => congrArg ofNat <| Nat.mod_add_div ..
   | succ m, -[n+1] => by
     show subNatNat (m % succ n) n + (↑(succ n * (m / succ n)) + n + 1) = (m + 1)
     rw [Int.add_comm _ n, ← Int.add_assoc, ← Int.add_assoc,
@@ -289,8 +289,8 @@ theorem fmod_eq_tmod {a b : Int} (Ha : 0 ≤ a) (Hb : 0 ≤ b) : fmod a b = tmod
 
 @[simp] protected theorem ediv_neg : ∀ a b : Int, a / (-b) = -(a / b)
   | ofNat m, 0 => show ofNat (m / 0) = -↑(m / 0) by rw [Nat.div_zero]; rfl
-  | ofNat m, -[n+1] => (Int.neg_neg _).symm
-  | ofNat m, succ n | -[m+1], 0 | -[m+1], succ n | -[m+1], -[n+1] => rfl
+  | ofNat _, -[_+1] => (Int.neg_neg _).symm
+  | ofNat _, succ _ | -[_+1], 0 | -[_+1], succ _ | -[_+1], -[_+1] => rfl
 
 theorem ediv_neg' {a b : Int} (Ha : a < 0) (Hb : 0 < b) : a / b < 0 :=
   match a, b, eq_negSucc_of_lt_zero Ha, eq_succ_of_zero_lt Hb with
@@ -339,7 +339,7 @@ theorem add_mul_ediv_right (a b : Int) {c : Int} (H : c ≠ 0) : (a + b * c) / c
       | _, ⟨k, rfl⟩, -[n+1] => show (a - n.succ * k.succ).ediv k.succ = a.ediv k.succ - n.succ by
         rw [← Int.add_sub_cancel (ediv ..), ← this, Int.sub_add_cancel]
   fun {k n} => @fun
-  | ofNat m => congrArg ofNat <| Nat.add_mul_div_right _ _ k.succ_pos
+  | ofNat _ => congrArg ofNat <| Nat.add_mul_div_right _ _ k.succ_pos
   | -[m+1] => by
     show ((n * k.succ : Nat) - m.succ : Int).ediv k.succ = n - (m / k.succ + 1 : Nat)
     by_cases h : m < n * k.succ
@@ -396,7 +396,7 @@ theorem add_mul_ediv_left (a : Int) {b : Int}
       rw [Int.mul_neg, Int.ediv_neg, Int.ediv_neg]; apply congrArg Neg.neg; apply this
   fun m k b =>
   match b, k with
-  | ofNat n, k => congrArg ofNat (Nat.mul_div_mul_left _ _ m.succ_pos)
+  | ofNat _, _ => congrArg ofNat (Nat.mul_div_mul_left _ _ m.succ_pos)
   | -[n+1], 0 => by
     rw [Int.ofNat_zero, Int.mul_zero, Int.ediv_zero, Int.ediv_zero]
   | -[n+1], succ k => congrArg negSucc <|
@@ -822,14 +822,14 @@ theorem ediv_eq_ediv_of_mul_eq_mul {a b c d : Int}
 unseal Nat.div in
 @[simp] protected theorem tdiv_neg : ∀ a b : Int, a.tdiv (-b) = -(a.tdiv b)
   | ofNat m, 0 => show ofNat (m / 0) = -↑(m / 0) by rw [Nat.div_zero]; rfl
-  | ofNat m, -[n+1] | -[m+1], succ n => (Int.neg_neg _).symm
-  | ofNat m, succ n | -[m+1], 0 | -[m+1], -[n+1] => rfl
+  | ofNat _, -[_+1] | -[_+1], succ _ => (Int.neg_neg _).symm
+  | ofNat _, succ _ | -[_+1], 0 | -[_+1], -[_+1] => rfl
 
 unseal Nat.div in
 @[simp] protected theorem neg_tdiv : ∀ a b : Int, (-a).tdiv b = -(a.tdiv b)
   | 0, n => by simp [Int.neg_zero]
-  | succ m, (n:Nat) | -[m+1], 0 | -[m+1], -[n+1] => rfl
-  | succ m, -[n+1] | -[m+1], succ n => (Int.neg_neg _).symm
+  | succ _, (n:Nat) | -[_+1], 0 | -[_+1], -[_+1] => rfl
+  | succ _, -[_+1] | -[_+1], succ _ => (Int.neg_neg _).symm
 
 protected theorem neg_tdiv_neg (a b : Int) : (-a).tdiv (-b) = a.tdiv b := by
   simp [Int.tdiv_neg, Int.neg_tdiv, Int.neg_neg]
@@ -1125,6 +1125,17 @@ theorem emod_add_bmod_congr (x : Int) (n : Nat) : Int.bmod (x%n + y) n = Int.bmo
   simp [Int.emod_def, Int.sub_eq_add_neg]
   rw [←Int.mul_neg, Int.add_right_comm,  Int.bmod_add_mul_cancel]
 
+@[simp]
+theorem emod_sub_bmod_congr (x : Int) (n : Nat) : Int.bmod (x%n - y) n = Int.bmod (x - y) n := by
+  simp only [emod_def, Int.sub_eq_add_neg]
+  rw [←Int.mul_neg, Int.add_right_comm,  Int.bmod_add_mul_cancel]
+
+@[simp]
+theorem sub_emod_bmod_congr (x : Int) (n : Nat) : Int.bmod (x - y%n) n = Int.bmod (x - y) n := by
+  simp only [emod_def]
+  rw [Int.sub_eq_add_neg, Int.neg_sub, Int.sub_eq_add_neg, ← Int.add_assoc, Int.add_right_comm,
+    Int.bmod_add_mul_cancel, Int.sub_eq_add_neg]
+
 @[simp]
 theorem emod_mul_bmod_congr (x : Int) (n : Nat) : Int.bmod (x%n * y) n = Int.bmod (x * y) n := by
   simp [Int.emod_def, Int.sub_eq_add_neg]
@@ -1140,9 +1151,28 @@ theorem bmod_add_bmod_congr : Int.bmod (Int.bmod x n + y) n = Int.bmod (x + y) n
     rw [Int.sub_eq_add_neg, Int.add_right_comm, ←Int.sub_eq_add_neg]
     simp
 
+@[simp]
+theorem bmod_sub_bmod_congr : Int.bmod (Int.bmod x n - y) n = Int.bmod (x - y) n := by
+  rw [Int.bmod_def x n]
+  split
+  next p =>
+    simp only [emod_sub_bmod_congr]
+  next p =>
+    rw [Int.sub_eq_add_neg, Int.sub_eq_add_neg, Int.add_right_comm, ←Int.sub_eq_add_neg, ← Int.sub_eq_add_neg]
+    simp [emod_sub_bmod_congr]
+
 @[simp] theorem add_bmod_bmod : Int.bmod (x + Int.bmod y n) n = Int.bmod (x + y) n := by
   rw [Int.add_comm x, Int.bmod_add_bmod_congr, Int.add_comm y]
 
+@[simp] theorem sub_bmod_bmod : Int.bmod (x - Int.bmod y n) n = Int.bmod (x - y) n := by
+  rw [Int.bmod_def y n]
+  split
+  next p =>
+    simp [sub_emod_bmod_congr]
+  next p =>
+    rw [Int.sub_eq_add_neg, Int.sub_eq_add_neg, Int.neg_add, Int.neg_neg, ← Int.add_assoc, ← Int.sub_eq_add_neg]
+    simp [sub_emod_bmod_congr]
+
 @[simp]
 theorem bmod_mul_bmod : Int.bmod (Int.bmod x n * y) n = Int.bmod (x * y) n := by
   rw [bmod_def x n]
@@ -1237,7 +1267,7 @@ theorem bmod_le {x : Int} {m : Nat} (h : 0 < m) : bmod x m ≤ (m - 1) / 2 := by
     _ = ((m + 1 - 2) + 2)/2 := by simp
     _ = (m - 1) / 2 + 1     := by
       rw [add_ediv_of_dvd_right]
-      · simp (config := {decide := true}) only [Int.ediv_self]
+      · simp +decide only [Int.ediv_self]
         congr 2
         rw [Int.add_sub_assoc, ← Int.sub_neg]
         congr
@@ -1255,7 +1285,7 @@ theorem bmod_natAbs_plus_one (x : Int) (w : 1 < x.natAbs) : bmod x (x.natAbs + 1
     simp only [bmod, ofNat_eq_coe, natAbs_ofNat, natCast_add, ofNat_one,
       emod_self_add_one (ofNat_nonneg x)]
     match x with
-    | 0 => rw [if_pos] <;> simp (config := {decide := true})
+    | 0 => rw [if_pos] <;> simp +decide
     | (x+1) =>
       rw [if_neg]
       · simp [← Int.sub_sub]

src/Init/Data/Int/Lemmas.lean

@@ -181,12 +181,12 @@ theorem subNatNat_add_negSucc (m n k : Nat) :
       Nat.add_comm]
 
 protected theorem add_assoc : ∀ a b c : Int, a + b + c = a + (b + c)
-  | (m:Nat), (n:Nat), c => aux1 ..
+  | (m:Nat), (n:Nat), _ => aux1 ..
   | Nat.cast m, b, Nat.cast k => by
     rw [Int.add_comm, ← aux1, Int.add_comm k, aux1, Int.add_comm b]
   | a, (n:Nat), (k:Nat) => by
     rw [Int.add_comm, Int.add_comm a, ← aux1, Int.add_comm a, Int.add_comm k]
-  | -[m+1], -[n+1], (k:Nat) => aux2 ..
+  | -[_+1], -[_+1], (k:Nat) => aux2 ..
   | -[m+1], (n:Nat), -[k+1] => by
     rw [Int.add_comm, ← aux2, Int.add_comm n, ← aux2, Int.add_comm -[m+1]]
   | (m:Nat), -[n+1], -[k+1] => by

src/Init/Data/Int/Order.lean

@@ -512,8 +512,8 @@ theorem toNat_add_nat {a : Int} (ha : 0 ≤ a) (n : Nat) : (a + n).toNat = a.toN
 
 @[simp] theorem pred_toNat : ∀ i : Int, (i - 1).toNat = i.toNat - 1
   | 0 => rfl
-  | (n+1:Nat) => by simp [ofNat_add]
-  | -[n+1] => rfl
+  | (_+1:Nat) => by simp [ofNat_add]
+  | -[_+1] => rfl
 
 theorem toNat_sub_toNat_neg : ∀ n : Int, ↑n.toNat - ↑(-n).toNat = n
   | 0 => rfl
@@ -1007,9 +1007,9 @@ theorem sign_eq_neg_one_iff_neg {a : Int} : sign a = -1 ↔ a < 0 :=
   match x with
   | 0 => rfl
   | .ofNat (_ + 1) =>
-    simp (config := { decide := true }) only [sign, true_iff]
+    simp +decide only [sign, true_iff]
     exact Int.le_add_one (ofNat_nonneg _)
-  | .negSucc _ => simp (config := { decide := true }) [sign]
+  | .negSucc _ => simp +decide [sign]
 
 theorem mul_sign : ∀ i : Int, i * sign i = natAbs i
   | succ _ => Int.mul_one _

src/Init/Data/Int/Pow.lean

@@ -5,6 +5,7 @@ Authors: Jeremy Avigad, Deniz Aydin, Floris van Doorn, Mario Carneiro
 -/
 prelude
 import Init.Data.Int.Lemmas
+import Init.Data.Nat.Lemmas
 
 namespace Int
 
@@ -35,10 +36,24 @@ theorem pow_le_pow_of_le_right {n : Nat} (hx : n > 0) {i : Nat} : ∀ {j}, i ≤
 theorem pos_pow_of_pos {n : Nat} (m : Nat) (h : 0 < n) : 0 < n^m :=
   pow_le_pow_of_le_right h (Nat.zero_le _)
 
+@[norm_cast]
 theorem natCast_pow (b n : Nat) : ((b^n : Nat) : Int) = (b : Int) ^ n := by
   match n with
   | 0 => rfl
   | n + 1 =>
     simp only [Nat.pow_succ, Int.pow_succ, natCast_mul, natCast_pow _ n]
 
+@[simp]
+protected theorem two_pow_pred_sub_two_pow {w : Nat} (h : 0 < w) :
+    ((2 ^ (w - 1) : Nat) - (2 ^ w : Nat) : Int) = - ((2 ^ (w - 1) : Nat) : Int) := by
+  rw [← Nat.two_pow_pred_add_two_pow_pred h]
+  omega
+
+@[simp]
+protected theorem two_pow_pred_sub_two_pow' {w : Nat} (h : 0 < w) :
+    (2 : Int) ^ (w - 1) - (2 : Int) ^ w = - (2 : Int) ^ (w - 1) := by
+  norm_cast
+  rw [← Nat.two_pow_pred_add_two_pow_pred h]
+  simp [h]
+
 end Int

src/Init/Data/List.lean

@@ -23,3 +23,6 @@ import Init.Data.List.TakeDrop
 import Init.Data.List.Zip
 import Init.Data.List.Perm
 import Init.Data.List.Sort
+import Init.Data.List.ToArray
+import Init.Data.List.MapIdx
+import Init.Data.List.OfFn

src/Init/Data/List/Attach.lean

@@ -73,7 +73,7 @@ theorem map_pmap {p : α → Prop} (g : β → γ) (f : ∀ a, p a → β) (l H)
   · 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
+    pmap g (map f l) H = pmap (fun a h => g (f a) h) l fun _ h => H _ (mem_map_of_mem _ h) := by
   induction l
   · rfl
   · simp only [*, pmap, map]
@@ -84,7 +84,7 @@ theorem attach_congr {l₁ l₂ : List α} (h : l₁ = l₂) :
   simp
 
 theorem attachWith_congr {l₁ l₂ : List α} (w : l₁ = l₂) {P : α → Prop} {H : ∀ x ∈ l₁, P x} :
-    l₁.attachWith P H = l₂.attachWith P fun x h => H _ (w ▸ h) := by
+    l₁.attachWith P H = l₂.attachWith P fun _ h => H _ (w ▸ h) := by
   subst w
   simp
 
@@ -169,6 +169,13 @@ theorem pmap_ne_nil_iff {P : α → Prop} (f : (a : α) → P a → β) {xs : Li
     (H : ∀ (a : α), a ∈ xs → P a) : xs.pmap f H ≠ [] ↔ xs ≠ [] := by
   simp
 
+theorem pmap_eq_self {l : List α} {p : α → Prop} (hp : ∀ (a : α), a ∈ l → p a)
+    (f : (a : α) → p a → α) : l.pmap f hp = l ↔ ∀ a (h : a ∈ l), f a (hp a h) = a := by
+  rw [pmap_eq_map_attach]
+  conv => lhs; rhs; rw [← attach_map_subtype_val l]
+  rw [map_inj_left]
+  simp
+
 @[simp]
 theorem attach_eq_nil_iff {l : List α} : l.attach = [] ↔ l = [] :=
   pmap_eq_nil_iff
@@ -353,7 +360,7 @@ theorem attach_map {l : List α} (f : α → β) :
   induction l <;> simp [*]
 
 theorem attachWith_map {l : List α} (f : α → β) {P : β → Prop} {H : ∀ (b : β), b ∈ l.map f → P b} :
-    (l.map f).attachWith P H = (l.attachWith (P ∘ f) (fun a h => H _ (mem_map_of_mem f h))).map
+    (l.map f).attachWith P H = (l.attachWith (P ∘ f) (fun _ h => H _ (mem_map_of_mem f h))).map
       fun ⟨x, h⟩ => ⟨f x, h⟩ := by
   induction l <;> simp [*]
 
@@ -548,4 +555,135 @@ theorem count_attachWith [DecidableEq α] {p : α → Prop} (l : List α) (H :
     (l.attachWith p H).count a = l.count ↑a :=
   Eq.trans (countP_congr fun _ _ => by simp [Subtype.ext_iff]) <| countP_attachWith _ _ _
 
+/-! ## unattach
+
+`List.unattach` is the (one-sided) inverse of `List.attach`. It is a synonym for `List.map Subtype.val`.
+
+We use it by providing a simp lemma `l.attach.unattach = l`, and simp lemmas which recognize higher order
+functions applied to `l : List { x // p x }` which only depend on the value, not the predicate, and rewrite these
+in terms of a simpler function applied to `l.unattach`.
+
+Further, we provide simp lemmas that push `unattach` inwards.
+-/
+
+/--
+A synonym for `l.map (·.val)`. Mostly this should not be needed by users.
+It is introduced as an intermediate step by lemmas such as `map_subtype`,
+and is ideally subsequently simplified away by `unattach_attach`.
+
+If not, usually the right approach is `simp [List.unattach, -List.map_subtype]` to unfold.
+-/
+def unattach {α : Type _} {p : α → Prop} (l : List { x // p x }) := l.map (·.val)
+
+@[simp] theorem unattach_nil {p : α → Prop} : ([] : List { x // p x }).unattach = [] := rfl
+@[simp] theorem unattach_cons {p : α → Prop} {a : { x // p x }} {l : List { x // p x }} :
+  (a :: l).unattach = a.val :: l.unattach := rfl
+
+@[simp] theorem length_unattach {p : α → Prop} {l : List { x // p x }} :
+    l.unattach.length = l.length := by
+  unfold unattach
+  simp
+
+@[simp] theorem unattach_attach {l : List α} : l.attach.unattach = l := by
+  unfold unattach
+  induction l with
+  | nil => simp
+  | cons a l ih => simp [ih, Function.comp_def]
+
+@[simp] theorem unattach_attachWith {p : α → Prop} {l : List α}
+    {H : ∀ a ∈ l, p a} :
+    (l.attachWith p H).unattach = l := by
+  unfold unattach
+  induction l with
+  | nil => simp
+  | cons a l ih => simp [ih, Function.comp_def]
+
+/-! ### Recognizing higher order functions on subtypes using a function that only depends on the value. -/
+
+/--
+This lemma identifies folds over lists of subtypes, where the function only depends on the value, not the proposition,
+and simplifies these to the function directly taking the value.
+-/
+@[simp] theorem foldl_subtype {p : α → Prop} {l : List { x // p x }}
+    {f : β → { x // p x } → β} {g : β → α → β} {x : β}
+    {hf : ∀ b x h, f b ⟨x, h⟩ = g b x} :
+    l.foldl f x = l.unattach.foldl g x := by
+  unfold unattach
+  induction l generalizing x with
+  | nil => simp
+  | cons a l ih => simp [ih, hf]
+
+/--
+This lemma identifies folds over lists of subtypes, where the function only depends on the value, not the proposition,
+and simplifies these to the function directly taking the value.
+-/
+@[simp] theorem foldr_subtype {p : α → Prop} {l : List { x // p x }}
+    {f : { x // p x } → β → β} {g : α → β → β} {x : β}
+    {hf : ∀ x h b, f ⟨x, h⟩ b = g x b} :
+    l.foldr f x = l.unattach.foldr g x := by
+  unfold unattach
+  induction l generalizing x with
+  | nil => simp
+  | cons a l ih => simp [ih, hf]
+
+/--
+This lemma identifies maps over lists of subtypes, where the function only depends on the value, not the proposition,
+and simplifies these to the function directly taking the value.
+-/
+@[simp] theorem map_subtype {p : α → Prop} {l : List { x // p x }}
+    {f : { x // p x } → β} {g : α → β} {hf : ∀ x h, f ⟨x, h⟩ = g x} :
+    l.map f = l.unattach.map g := by
+  unfold unattach
+  induction l with
+  | nil => simp
+  | cons a l ih => simp [ih, hf]
+
+@[simp] theorem filterMap_subtype {p : α → Prop} {l : List { x // p x }}
+    {f : { x // p x } → Option β} {g : α → Option β} {hf : ∀ x h, f ⟨x, h⟩ = g x} :
+    l.filterMap f = l.unattach.filterMap g := by
+  unfold unattach
+  induction l with
+  | nil => simp
+  | cons a l ih => simp [ih, hf, filterMap_cons]
+
+@[simp] theorem flatMap_subtype {p : α → Prop} {l : List { x // p x }}
+    {f : { x // p x } → List β} {g : α → List β} {hf : ∀ x h, f ⟨x, h⟩ = g x} :
+    (l.flatMap f) = l.unattach.flatMap g := by
+  unfold unattach
+  induction l with
+  | nil => simp
+  | cons a l ih => simp [ih, hf]
+
+@[deprecated flatMap_subtype (since := "2024-10-16")] abbrev bind_subtype := @flatMap_subtype
+
+@[simp] theorem unattach_filter {p : α → Prop} {l : List { x // p x }}
+    {f : { x // p x } → Bool} {g : α → Bool} {hf : ∀ x h, f ⟨x, h⟩ = g x} :
+    (l.filter f).unattach = l.unattach.filter g := by
+  induction l with
+  | nil => simp
+  | cons a l ih =>
+    simp only [filter_cons, hf, unattach_cons]
+    split <;> simp [ih]
+
+/-! ### Simp lemmas pushing `unattach` inwards. -/
+
+@[simp] theorem unattach_reverse {p : α → Prop} {l : List { x // p x }} :
+    l.reverse.unattach = l.unattach.reverse := by
+  simp [unattach, -map_subtype]
+
+@[simp] theorem unattach_append {p : α → Prop} {l₁ l₂ : List { x // p x }} :
+    (l₁ ++ l₂).unattach = l₁.unattach ++ l₂.unattach := by
+  simp [unattach, -map_subtype]
+
+@[simp] theorem unattach_flatten {p : α → Prop} {l : List (List { x // p x })} :
+    l.flatten.unattach = (l.map unattach).flatten := by
+  unfold unattach
+  induction l <;> simp_all
+
+@[deprecated unattach_flatten (since := "2024-10-14")] abbrev unattach_join := @unattach_flatten
+
+@[simp] theorem unattach_replicate {p : α → Prop} {n : Nat} {x : { x // p x }} :
+    (List.replicate n x).unattach = List.replicate n x.1 := by
+  simp [unattach, -map_subtype]
+
 end List

src/Init/Data/List/Basic.lean

@@ -29,22 +29,23 @@ The operations are organized as follow:
 * 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
+  `map`, `filter`, `filterMap`, `foldr`, `append`, `flatten`, `pure`, `flatMap`, `replicate`, and
   `reverse`.
 * Additional functions defined in terms of these: `leftpad`, `rightPad`, and `reduceOption`.
+* Operations using indexes: `mapIdx`.
 * 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`.
+* Manipulating elements: `replace`, `modify`, `insert`, `insertIdx`, `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`,
+* Minima and maxima: `min?` and `max?`.
+* Other functions: `intersperse`, `intercalate`, `eraseDups`, `eraseReps`, `span`, `splitBy`,
   `removeAll`
   (currently these functions are mostly only used in meta code,
   and do not have API suitable for verification).
@@ -121,6 +122,11 @@ protected def beq [BEq α] : List α → List α → Bool
   | a::as, b::bs => a == b && List.beq as bs
   | _,     _     => false
 
+@[simp] theorem beq_nil_nil [BEq α] : List.beq ([] : List α) ([] : List α) = true := rfl
+@[simp] theorem beq_cons_nil [BEq α] (a : α) (as : List α) : List.beq (a::as) [] = false := rfl
+@[simp] theorem beq_nil_cons [BEq α] (a : α) (as : List α) : List.beq [] (a::as) = false := rfl
+theorem beq_cons₂ [BEq α] (a b : α) (as bs : List α) : List.beq (a::as) (b::bs) = (a == b && List.beq as bs) := rfl
+
 instance [BEq α] : BEq (List α) := ⟨List.beq⟩
 
 instance [BEq α] [LawfulBEq α] : LawfulBEq (List α) where
@@ -218,8 +224,8 @@ def get? : (as : List α) → (i : Nat) → Option α
 
 theorem ext_get? : ∀ {l₁ l₂ : List α}, (∀ n, l₁.get? n = l₂.get? n) → l₁ = l₂
   | [], [], _ => rfl
-  | a :: l₁, [], h => nomatch h 0
-  | [], a' :: l₂, h => nomatch h 0
+  | _ :: _, [], h => nomatch h 0
+  | [], _ :: _, h => nomatch h 0
   | a :: l₁, a' :: l₂, h => by
     have h0 : some a = some a' := h 0
     injection h0 with aa; simp only [aa, ext_get? fun n => h (n+1)]
@@ -368,7 +374,7 @@ def tailD (list fallback : List α) : List α :=
 /-! ## Basic `List` operations.
 
 We define the basic functional programming operations on `List`:
-`map`, `filter`, `filterMap`, `foldr`, `append`, `join`, `pure`, `bind`, `replicate`, and `reverse`.
+`map`, `filter`, `filterMap`, `foldr`, `append`, `flatten`, `pure`, `bind`, `replicate`, and `reverse`.
 -/
 
 /-! ### map -/
@@ -542,41 +548,53 @@ theorem reverseAux_eq_append (as bs : List α) : reverseAux as bs = reverseAux a
   simp [reverse, reverseAux]
   rw [← reverseAux_eq_append]
 
-/-! ### join -/
+/-! ### flatten -/
 
 /--
-`O(|join L|)`. `join L` concatenates all the lists in `L` into one list.
-* `join [[a], [], [b, c], [d, e, f]] = [a, b, c, d, e, f]`
+`O(|flatten L|)`. `join L` concatenates all the lists in `L` into one list.
+* `flatten [[a], [], [b, c], [d, e, f]] = [a, b, c, d, e, f]`
 -/
-def join : List (List α) → List α
+def flatten : List (List α) → List α
   | []      => []
-  | a :: as => a ++ join as
+  | a :: as => a ++ flatten as
 
-@[simp] theorem join_nil : List.join ([] : List (List α)) = [] := rfl
-@[simp] theorem join_cons : (l :: ls).join = l ++ ls.join := rfl
+@[simp] theorem flatten_nil : List.flatten ([] : List (List α)) = [] := rfl
+@[simp] theorem flatten_cons : (l :: ls).flatten = l ++ ls.flatten := rfl
 
-/-! ### pure -/
+@[deprecated flatten (since := "2024-10-14"), inherit_doc flatten] abbrev join := @flatten
 
-/-- `pure x = [x]` is the `pure` operation of the list monad. -/
-@[inline] protected def pure {α : Type u} (a : α) : List α := [a]
+/-! ### singleton -/
 
-/-! ### bind -/
+/-- `singleton x = [x]`. -/
+@[inline] protected def singleton {α : Type u} (a : α) : List α := [a]
+
+set_option linter.missingDocs false in
+@[deprecated singleton (since := "2024-10-16")] protected abbrev pure := @singleton
+
+/-! ### flatMap -/
 
 /--
-`bind xs f` is the bind operation of the list monad. It applies `f` to each element of `xs`
+`flatMap xs f` applies `f` to each element of `xs`
 to get a list of lists, and then concatenates them all together.
 * `[2, 3, 2].bind range = [0, 1, 0, 1, 2, 0, 1]`
 -/
-@[inline] protected def bind {α : Type u} {β : Type v} (a : List α) (b : α → List β) : List β := join (map b a)
+@[inline] def flatMap {α : Type u} {β : Type v} (a : List α) (b : α → List β) : List β := flatten (map b a)
 
-@[simp] theorem bind_nil (f : α → List β) : List.bind [] f = [] := by simp [join, List.bind]
-@[simp] theorem bind_cons x xs (f : α → List β) :
-  List.bind (x :: xs) f = f x ++ List.bind xs f := by simp [join, List.bind]
+@[simp] theorem flatMap_nil (f : α → List β) : List.flatMap [] f = [] := by simp [flatten, List.flatMap]
+@[simp] theorem flatMap_cons x xs (f : α → List β) :
+  List.flatMap (x :: xs) f = f x ++ List.flatMap xs f := by simp [flatten, List.flatMap]
 
 set_option linter.missingDocs false in
-@[deprecated bind_nil (since := "2024-06-15")] abbrev nil_bind := @bind_nil
+@[deprecated flatMap (since := "2024-10-16")] abbrev bind := @flatMap
 set_option linter.missingDocs false in
-@[deprecated bind_cons (since := "2024-06-15")] abbrev cons_bind := @bind_cons
+@[deprecated flatMap_nil (since := "2024-10-16")] abbrev nil_flatMap := @flatMap_nil
+set_option linter.missingDocs false in
+@[deprecated flatMap_cons (since := "2024-10-16")] abbrev cons_flatMap := @flatMap_cons
+
+set_option linter.missingDocs false in
+@[deprecated flatMap_nil (since := "2024-06-15")] abbrev nil_bind := @flatMap_nil
+set_option linter.missingDocs false in
+@[deprecated flatMap_cons (since := "2024-06-15")] abbrev cons_bind := @flatMap_cons
 
 /-! ### replicate -/
 
@@ -1095,12 +1113,50 @@ theorem replace_cons [BEq α] {a : α} :
     (a::as).replace b c = match b == a with | true => c::as | false => a :: replace as b c :=
   rfl
 
+/-! ### modify -/
+
+/--
+Apply a function to the nth tail of `l`. Returns the input without
+using `f` if the index is larger than the length of the List.
+```
+modifyTailIdx f 2 [a, b, c] = [a, b] ++ f [c]
+```
+-/
+@[simp] def modifyTailIdx (f : List α → List α) : Nat → List α → List α
+  | 0, l => f l
+  | _+1, [] => []
+  | n+1, a :: l => a :: modifyTailIdx f n l
+
+/-- Apply `f` to the head of the list, if it exists. -/
+@[inline] def modifyHead (f : α → α) : List α → List α
+  | [] => []
+  | a :: l => f a :: l
+
+@[simp] theorem modifyHead_nil (f : α → α) : [].modifyHead f = [] := by rw [modifyHead]
+@[simp] theorem modifyHead_cons (a : α) (l : List α) (f : α → α) :
+    (a :: l).modifyHead f = f a :: l := by rw [modifyHead]
+
+/--
+Apply `f` to the nth element of the list, if it exists, replacing that element with the result.
+-/
+def modify (f : α → α) : Nat → List α → List α :=
+  modifyTailIdx (modifyHead f)
+
 /-! ### insert -/
 
 /-- Inserts an element into a list without duplication. -/
 @[inline] protected def insert [BEq α] (a : α) (l : List α) : List α :=
   if l.elem a then l else a :: l
 
+/--
+`insertIdx n a l` inserts `a` into the list `l` after the first `n` elements of `l`
+```
+insertIdx 2 1 [1, 2, 3, 4] = [1, 2, 1, 3, 4]
+```
+-/
+def insertIdx (n : Nat) (a : α) : List α → List α :=
+  modifyTailIdx (cons a) n
+
 /-! ### erase -/
 
 /--
@@ -1395,12 +1451,25 @@ def unzip : List (α × β) → List α × List β
 
 /-! ## Ranges and enumeration -/
 
+/-- Sum of a list.
+
+`List.sum [a, b, c] = a + (b + (c + 0))` -/
+def sum {α} [Add α] [Zero α] : List α → α :=
+  foldr (· + ·) 0
+
+@[simp] theorem sum_nil [Add α] [Zero α] : ([] : List α).sum = 0 := rfl
+@[simp] theorem sum_cons [Add α] [Zero α] {a : α} {l : List α} : (a::l).sum = a + l.sum := rfl
+
 /-- Sum of a list of natural numbers. -/
--- This is not in the `List` namespace as later `List.sum` will be defined polymorphically.
+@[deprecated List.sum (since := "2024-10-17")]
 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) :
+set_option linter.deprecated false in
+@[simp, deprecated sum_nil (since := "2024-10-17")]
+theorem _root_.Nat.sum_nil : Nat.sum ([] : List Nat) = 0 := rfl
+set_option linter.deprecated false in
+@[simp, deprecated sum_cons (since := "2024-10-17")]
+theorem _root_.Nat.sum_cons (a : Nat) (l : List Nat) :
     Nat.sum (a::l) = a + Nat.sum l := rfl
 
 /-! ### range -/
@@ -1464,30 +1533,34 @@ def enum : List α → List (Nat × α) := enumFrom 0
 
 /-! ## Minima and maxima -/
 
-/-! ### minimum? -/
+/-! ### min? -/
 
 /--
 Returns the smallest element of the list, if it is not empty.
-* `[].minimum? = none`
-* `[4].minimum? = some 4`
-* `[1, 4, 2, 10, 6].minimum? = some 1`
+* `[].min? = none`
+* `[4].min? = some 4`
+* `[1, 4, 2, 10, 6].min? = some 1`
 -/
-def minimum? [Min α] : List α → Option α
+def min? [Min α] : List α → Option α
   | []    => none
   | a::as => some <| as.foldl min a
 
-/-! ### maximum? -/
+@[inherit_doc min?, deprecated min? (since := "2024-09-29")] abbrev minimum? := @min?
+
+/-! ### max? -/
 
 /--
 Returns the largest element of the list, if it is not empty.
-* `[].maximum? = none`
-* `[4].maximum? = some 4`
-* `[1, 4, 2, 10, 6].maximum? = some 10`
+* `[].max? = none`
+* `[4].max? = some 4`
+* `[1, 4, 2, 10, 6].max? = some 10`
 -/
-def maximum? [Max α] : List α → Option α
+def max? [Max α] : List α → Option α
   | []    => none
   | a::as => some <| as.foldl max a
 
+@[inherit_doc max?, deprecated max? (since := "2024-09-29")] abbrev maximum? := @max?
+
 /-! ## Other list operations
 
 The functions are currently mostly used in meta code,
@@ -1523,7 +1596,7 @@ def intersperse (sep : α) : List α → List α
 * `intercalate sep [a, b, c] = a ++ sep ++ b ++ sep ++ c`
 -/
 def intercalate (sep : List α) (xs : List (List α)) : List α :=
-  join (intersperse sep xs)
+  (intersperse sep xs).flatten
 
 /-! ### eraseDups -/
 
@@ -1575,23 +1648,23 @@ where
     | true  => loop as (a::rs)
     | false => (rs.reverse, a::as)
 
-/-! ### groupBy -/
+/-! ### splitBy -/
 
 /--
-`O(|l|)`. `groupBy R l` splits `l` into chains of elements
+`O(|l|)`. `splitBy R l` splits `l` into chains of elements
 such that adjacent elements are related by `R`.
 
-* `groupBy (·==·) [1, 1, 2, 2, 2, 3, 2] = [[1, 1], [2, 2, 2], [3], [2]]`
-* `groupBy (·<·) [1, 2, 5, 4, 5, 1, 4] = [[1, 2, 5], [4, 5], [1, 4]]`
+* `splitBy (·==·) [1, 1, 2, 2, 2, 3, 2] = [[1, 1], [2, 2, 2], [3], [2]]`
+* `splitBy (·<·) [1, 2, 5, 4, 5, 1, 4] = [[1, 2, 5], [4, 5], [1, 4]]`
 -/
-@[specialize] def groupBy (R : α → α → Bool) : List α → List (List α)
+@[specialize] def splitBy (R : α → α → Bool) : List α → List (List α)
   | []    => []
   | a::as => loop as a [] []
 where
   /--
-  The arguments of `groupBy.loop l ag g gs` represent the following:
+  The arguments of `splitBy.loop l ag g gs` represent the following:
 
-  - `l : List α` are the elements which we still need to group.
+  - `l : List α` are the elements which we still need to split.
   - `ag : α` is the previous element for which a comparison was performed.
   - `g : List α` is the group currently being assembled, in **reverse order**.
   - `gs : List (List α)` is all of the groups that have been completed, in **reverse order**.
@@ -1602,6 +1675,8 @@ where
     | false => loop as a [] ((ag::g).reverse::gs)
   | [], ag, g, gs => ((ag::g).reverse::gs).reverse
 
+@[deprecated splitBy (since := "2024-10-30"), inherit_doc splitBy] abbrev groupBy := @splitBy
+
 /-! ### removeAll -/
 
 /-- `O(|xs|)`. Computes the "set difference" of lists,

src/Init/Data/List/BasicAux.lean

@@ -232,11 +232,12 @@ theorem sizeOf_get [SizeOf α] (as : List α) (i : Fin as.length) : sizeOf (as.g
     apply Nat.lt_trans ih
     simp_arith
 
-theorem le_antisymm [LT α] [s : Antisymm (¬ · < · : α → α → Prop)] {as bs : List α} (h₁ : as ≤ bs) (h₂ : bs ≤ as) : as = bs :=
+theorem le_antisymm [LT α] [s : Std.Antisymm (¬ · < · : α → α → Prop)]
+    {as bs : List α} (h₁ : as ≤ bs) (h₂ : bs ≤ as) : as = bs :=
   match as, bs with
   | [],    []    => rfl
-  | [],    b::bs => False.elim <| h₂ (List.lt.nil ..)
-  | a::as, []    => False.elim <| h₁ (List.lt.nil ..)
+  | [],    _::_ => False.elim <| h₂ (List.lt.nil ..)
+  | _::_, []    => False.elim <| h₁ (List.lt.nil ..)
   | a::as, b::bs => by
     by_cases hab : a < b
     · exact False.elim <| h₂ (List.lt.head _ _ hab)
@@ -248,7 +249,8 @@ theorem le_antisymm [LT α] [s : Antisymm (¬ · < · : α → α → Prop)] {as
         have : a = b := s.antisymm hab hba
         simp [this, ih]
 
-instance [LT α] [Antisymm (¬ · < · : α → α → Prop)] : Antisymm (· ≤ · : List α → List α → Prop) where
+instance [LT α] [Std.Antisymm (¬ · < · : α → α → Prop)] :
+    Std.Antisymm (· ≤ · : List α → List α → Prop) where
   antisymm h₁ h₂ := le_antisymm h₁ h₂
 
 end List

src/Init/Data/List/Control.lean

@@ -5,6 +5,8 @@ Author: Leonardo de Moura
 -/
 prelude
 import Init.Control.Basic
+import Init.Control.Id
+import Init.Control.Lawful
 import Init.Data.List.Basic
 
 namespace List
@@ -207,6 +209,16 @@ def findM? {m : Type → Type u} [Monad m] {α : Type} (p : α → m Bool) : Lis
     | true  => pure (some a)
     | false => findM? p as
 
+@[simp]
+theorem findM?_id (p : α → Bool) (as : List α) : findM? (m := Id) p as = as.find? p := by
+  induction as with
+  | nil => rfl
+  | cons a as ih =>
+    simp only [findM?, find?]
+    cases p a with
+    | true  => rfl
+    | false => rw [ih]; rfl
+
 @[specialize]
 def findSomeM? {m : Type u → Type v} [Monad m] {α : Type w} {β : Type u} (f : α → m (Option β)) : List α → m (Option β)
   | []    => pure none
@@ -215,26 +227,27 @@ def findSomeM? {m : Type u → Type v} [Monad m] {α : Type w} {β : Type u} (f
     | some b => pure (some b)
     | none   => findSomeM? f as
 
-@[inline] protected def forIn {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m] (as : List α) (init : β) (f : α → β → m (ForInStep β)) : m β :=
-  let rec @[specialize] loop
-    | [], b    => pure b
-    | a::as, b => do
-      match (← f a b) with
-      | ForInStep.done b  => pure b
-      | ForInStep.yield b => loop as b
-  loop as init
+@[simp]
+theorem findSomeM?_id (f : α → Option β) (as : List α) : findSomeM? (m := Id) f as = as.findSome? f := by
+  induction as with
+  | nil => rfl
+  | cons a as ih =>
+    simp only [findSomeM?, findSome?]
+    cases f a with
+    | some b => rfl
+    | none   => rw [ih]; rfl
 
-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
-
-@[simp] theorem forIn_cons [Monad m] (f : α → β → m (ForInStep β)) (a : α) (as : List α) (b : β)
-    : forIn (a::as) b f = f a b >>= fun | ForInStep.done b => pure b | ForInStep.yield b => forIn as b f :=
-  rfl
+theorem findM?_eq_findSomeM? [Monad m] [LawfulMonad m] (p : α → m Bool) (as : List α) :
+    as.findM? p = as.findSomeM? fun a => return if (← p a) then some a else none := by
+  induction as with
+  | nil => rfl
+  | cons a as ih =>
+    simp only [findM?, findSomeM?]
+    simp [ih]
+    congr
+    apply funext
+    intro b
+    cases b <;> simp
 
 @[inline] protected def forIn' {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m] (as : List α) (init : β) (f : (a : α) → a ∈ as → β → m (ForInStep β)) : m β :=
   let rec @[specialize] loop : (as' : List α) → (b : β) → Exists (fun bs => bs ++ as' = as) → m β
@@ -254,14 +267,15 @@ instance : ForIn m (List α) α where
 instance : ForIn' m (List α) α inferInstance where
   forIn' := List.forIn'
 
-@[simp] theorem forIn'_eq_forIn {α : Type u} {β : Type v} {m : Type v → Type w} [Monad m] (as : List α) (init : β) (f : α → β → m (ForInStep β)) : forIn' as init (fun a _ b => f a b) = forIn as init f := by
-  simp [forIn', forIn, List.forIn, List.forIn']
-  have : ∀ cs h, List.forIn'.loop cs (fun a _ b => f a b) as init h = List.forIn.loop f as init := by
-    intro cs h
-    induction as generalizing cs init with
-    | nil => intros; rfl
-    | cons a as ih => intros; simp [List.forIn.loop, List.forIn'.loop, ih]
-  apply this
+-- No separate `ForIn` instance is required because it can be derived from `ForIn'`.
+
+@[simp] theorem forIn'_eq_forIn' [Monad m] : @List.forIn' α β m _ = forIn' := rfl
+
+@[simp] theorem forIn'_nil [Monad m] (f : (a : α) → a ∈ [] → β → m (ForInStep β)) (b : β) : forIn' [] b f = pure b :=
+  rfl
+
+@[simp] theorem forIn_nil [Monad m] (f : α → β → m (ForInStep β)) (b : β) : forIn [] b f = pure b :=
+  rfl
 
 instance : ForM m (List α) α where
   forM := List.forM

src/Init/Data/List/Count.lean

@@ -153,13 +153,15 @@ theorem countP_filterMap (p : β → Bool) (f : α → Option β) (l : List α)
   simp only [length_filterMap_eq_countP]
   congr
   ext a
-  simp (config := { contextual := true }) [Option.getD_eq_iff]
+  simp +contextual [Option.getD_eq_iff, Option.isSome_eq_isSome]
 
-@[simp] theorem countP_join (l : List (List α)) :
-    countP p l.join = Nat.sum (l.map (countP p)) := by
-  simp only [countP_eq_length_filter, filter_join]
+@[simp] theorem countP_flatten (l : List (List α)) :
+    countP p l.flatten = (l.map (countP p)).sum := by
+  simp only [countP_eq_length_filter, filter_flatten]
   simp [countP_eq_length_filter']
 
+@[deprecated countP_flatten (since := "2024-10-14")] abbrev countP_join := @countP_flatten
+
 @[simp] theorem countP_reverse (l : List α) : countP p l.reverse = countP p l := by
   simp [countP_eq_length_filter, filter_reverse]
 
@@ -230,8 +232,10 @@ theorem count_singleton (a b : α) : count a [b] = if b == a then 1 else 0 := by
 @[simp] theorem count_append (a : α) : ∀ l₁ l₂, count a (l₁ ++ l₂) = count a l₁ + count a l₂ :=
   countP_append _
 
-theorem count_join (a : α) (l : List (List α)) : count a l.join = Nat.sum (l.map (count a)) := by
-  simp only [count_eq_countP, countP_join, count_eq_countP']
+theorem count_flatten (a : α) (l : List (List α)) : count a l.flatten = (l.map (count a)).sum := by
+  simp only [count_eq_countP, countP_flatten, count_eq_countP']
+
+@[deprecated count_flatten (since := "2024-10-14")] abbrev count_join := @count_flatten
 
 @[simp] theorem count_reverse (a : α) (l : List α) : count a l.reverse = count a l := by
   simp only [count_eq_countP, countP_eq_length_filter, filter_reverse, length_reverse]
@@ -311,7 +315,7 @@ theorem replicate_count_eq_of_count_eq_length {l : List α} (h : count a l = len
 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 })
+  apply countP_mono_left; simp +contextual
 
 theorem count_filterMap {α} [BEq β] (b : β) (f : α → Option β) (l : List α) :
     count b (filterMap f l) = countP (fun a => f a == some b) l := by

src/Init/Data/List/Erase.lean

@@ -52,9 +52,9 @@ theorem eraseP_of_forall_not {l : List α} (h : ∀ a, a ∈ l → ¬p a) : l.er
 theorem eraseP_ne_nil {xs : List α} {p : α → Bool} : xs.eraseP p ≠ [] ↔ xs ≠ [] ∧ ∀ x, p x → xs ≠ [x] := by
   simp
 
-theorem exists_of_eraseP : ∀ {l : List α} {a} (al : a ∈ l) (pa : p a),
+theorem exists_of_eraseP : ∀ {l : List α} {a} (_ : a ∈ l) (_ : 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 =>
+  | b :: l, _, al, pa =>
     if pb : p b then
       ⟨b, [], l, forall_mem_nil _, pb, by simp [pb]⟩
     else
@@ -168,8 +168,8 @@ theorem eraseP_append_left {a : α} (pa : p a) :
 
 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
+  | [],     _, _ => rfl
+  | _ :: _, _, 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) :

src/Init/Data/List/Find.lean

@@ -10,7 +10,8 @@ import Init.Data.List.Sublist
 import Init.Data.List.Range
 
 /-!
-# Lemmas about `List.findSome?`, `List.find?`, `List.findIdx`, `List.findIdx?`, and `List.indexOf`.
+Lemmas about `List.findSome?`, `List.find?`, `List.findIdx`, `List.findIdx?`, `List.indexOf`,
+and `List.lookup`.
 -/
 
 namespace List
@@ -95,22 +96,22 @@ theorem findSome?_eq_some_iff {f : α → Option β} {l : List α} {b : β} :
     · simp only [Option.guard_eq_none] at h
       simp [ih, h]
 
-@[simp] theorem filterMap_head? (f : α → Option β) (l : List α) : (l.filterMap f).head? = l.findSome? f := by
+@[simp] theorem head?_filterMap (f : α → Option β) (l : List α) : (l.filterMap f).head? = l.findSome? f := by
   induction l with
   | nil => simp
   | cons x xs ih =>
     simp only [filterMap_cons, findSome?_cons]
     split <;> simp [*]
 
-@[simp] theorem filterMap_head (f : α → Option β) (l : List α) (h) :
-    (l.filterMap f).head h = (l.findSome? f).get (by simp_all [Option.isSome_iff_ne_none])  := by
+@[simp] theorem head_filterMap (f : α → Option β) (l : List α) (h) :
+    (l.filterMap f).head h = (l.findSome? f).get (by simp_all [Option.isSome_iff_ne_none]) := by
   simp [head_eq_iff_head?_eq_some]
 
-@[simp] theorem filterMap_getLast? (f : α → Option β) (l : List α) : (l.filterMap f).getLast? = l.reverse.findSome? f := by
+@[simp] theorem getLast?_filterMap (f : α → Option β) (l : List α) : (l.filterMap f).getLast? = l.reverse.findSome? f := by
   rw [getLast?_eq_head?_reverse]
   simp [← filterMap_reverse]
 
-@[simp] theorem filterMap_getLast (f : α → Option β) (l : List α) (h) :
+@[simp] theorem getLast_filterMap (f : α → Option β) (l : List α) (h) :
     (l.filterMap f).getLast h = (l.reverse.findSome? f).get (by simp_all [Option.isSome_iff_ne_none]) := by
   simp [getLast_eq_iff_getLast_eq_some]
 
@@ -132,14 +133,14 @@ theorem findSome?_append {l₁ l₂ : List α} : (l₁ ++ l₂).findSome? f = (l
     simp only [cons_append, findSome?]
     split <;> simp_all
 
-theorem head_join {L : List (List α)} (h : ∃ l, l ∈ L ∧ l ≠ []) :
-    (join L).head (by simpa using h) = (L.findSome? fun l => l.head?).get (by simpa using h) := by
-  simp [head_eq_iff_head?_eq_some, head?_join]
+theorem head_flatten {L : List (List α)} (h : ∃ l, l ∈ L ∧ l ≠ []) :
+    (flatten L).head (by simpa using h) = (L.findSome? fun l => l.head?).get (by simpa using h) := by
+  simp [head_eq_iff_head?_eq_some, head?_flatten]
 
-theorem getLast_join {L : List (List α)} (h : ∃ l, l ∈ L ∧ l ≠ []) :
-    (join L).getLast (by simpa using h) =
+theorem getLast_flatten {L : List (List α)} (h : ∃ l, l ∈ L ∧ l ≠ []) :
+    (flatten L).getLast (by simpa using h) =
       (L.reverse.findSome? fun l => l.getLast?).get (by simpa using h) := by
-  simp [getLast_eq_iff_getLast_eq_some, getLast?_join]
+  simp [getLast_eq_iff_getLast_eq_some, getLast?_flatten]
 
 theorem findSome?_replicate : findSome? f (replicate n a) = if n = 0 then none else f a := by
   cases n with
@@ -179,7 +180,7 @@ theorem IsPrefix.findSome?_eq_some {l₁ l₂ : List α} {f : α → Option β}
     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]
+  simp +contextual [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 :=
@@ -206,7 +207,8 @@ theorem IsInfix.findSome?_eq_none {l₁ l₂ : List α} {f : α → Option β} (
 @[simp] theorem find?_eq_none : find? p l = none ↔ ∀ x ∈ l, ¬ p x := by
   induction l <;> simp [find?_cons]; split <;> simp [*]
 
-theorem find?_eq_some : xs.find? p = some b ↔ p b ∧ ∃ as bs, xs = as ++ b :: bs ∧ ∀ a ∈ as, !p a := by
+theorem find?_eq_some_iff_append :
+    xs.find? p = some b ↔ p b ∧ ∃ as bs, xs = as ++ b :: bs ∧ ∀ a ∈ as, !p a := by
   induction xs with
   | nil => simp
   | cons x xs ih =>
@@ -242,6 +244,9 @@ theorem find?_eq_some : xs.find? p = some b ↔ p b ∧ ∃ as bs, xs = as ++ b
           cases h₁
           simp
 
+@[deprecated find?_eq_some_iff_append (since := "2024-11-06")]
+abbrev find?_eq_some := @find?_eq_some_iff_append
+
 @[simp]
 theorem find?_cons_eq_some : (a :: xs).find? p = some b ↔ (p a ∧ a = b) ∨ (!p a ∧ xs.find? p = some b) := by
   rw [find?_cons]
@@ -287,18 +292,18 @@ theorem get_find?_mem (xs : List α) (p : α → Bool) (h) : (xs.find? p).get h
     · simp only [find?_cons]
       split <;> simp_all
 
-@[simp] theorem filter_head? (p : α → Bool) (l : List α) : (l.filter p).head? = l.find? p := by
-  rw [← filterMap_eq_filter, filterMap_head?, findSome?_guard]
+@[simp] theorem head?_filter (p : α → Bool) (l : List α) : (l.filter p).head? = l.find? p := by
+  rw [← filterMap_eq_filter, head?_filterMap, findSome?_guard]
 
-@[simp] theorem filter_head (p : α → Bool) (l : List α) (h) :
+@[simp] theorem head_filter (p : α → Bool) (l : List α) (h) :
     (l.filter p).head h = (l.find? p).get (by simp_all [Option.isSome_iff_ne_none]) := by
   simp [head_eq_iff_head?_eq_some]
 
-@[simp] theorem filter_getLast? (p : α → Bool) (l : List α) : (l.filter p).getLast? = l.reverse.find? p := by
+@[simp] theorem getLast?_filter (p : α → Bool) (l : List α) : (l.filter p).getLast? = l.reverse.find? p := by
   rw [getLast?_eq_head?_reverse]
   simp [← filter_reverse]
 
-@[simp] theorem filter_getLast (p : α → Bool) (l : List α) (h) :
+@[simp] theorem getLast_filter (p : α → Bool) (l : List α) (h) :
     (l.filter p).getLast h = (l.reverse.find? p).get (by simp_all [Option.isSome_iff_ne_none]) := by
   simp [getLast_eq_iff_getLast_eq_some]
 
@@ -326,35 +331,35 @@ theorem get_find?_mem (xs : List α) (p : α → Bool) (h) : (xs.find? p).get h
     simp only [cons_append, find?]
     by_cases h : p x <;> simp [h, ih]
 
-@[simp] theorem find?_join (xs : List (List α)) (p : α → Bool) :
-    xs.join.find? p = xs.findSome? (·.find? p) := by
+@[simp] theorem find?_flatten (xs : List (List α)) (p : α → Bool) :
+    xs.flatten.find? p = xs.findSome? (·.find? p) := by
   induction xs with
   | nil => simp
   | cons x xs ih =>
-    simp only [join_cons, find?_append, findSome?_cons, ih]
+    simp only [flatten_cons, find?_append, findSome?_cons, ih]
     split <;> simp [*]
 
-theorem find?_join_eq_none {xs : List (List α)} {p : α → Bool} :
-    xs.join.find? p = none ↔ ∀ ys ∈ xs, ∀ x ∈ ys, !p x := by
+theorem find?_flatten_eq_none {xs : List (List α)} {p : α → Bool} :
+    xs.flatten.find? p = none ↔ ∀ ys ∈ xs, ∀ x ∈ ys, !p x := by
   simp
 
 /--
-If `find? p` returns `some a` from `xs.join`, then `p a` holds, and
+If `find? p` returns `some a` from `xs.flatten`, then `p a` holds, and
 some list in `xs` contains `a`, and no earlier element of that list satisfies `p`.
 Moreover, no earlier list in `xs` has an element satisfying `p`.
 -/
-theorem find?_join_eq_some {xs : List (List α)} {p : α → Bool} {a : α} :
-    xs.join.find? p = some a ↔
+theorem find?_flatten_eq_some {xs : List (List α)} {p : α → Bool} {a : α} :
+    xs.flatten.find? p = some a ↔
       p a ∧ ∃ as ys zs bs, xs = as ++ (ys ++ a :: zs) :: bs ∧
         (∀ a ∈ as, ∀ x ∈ a, !p x) ∧ (∀ x ∈ ys, !p x) := by
-  rw [find?_eq_some]
+  rw [find?_eq_some_iff_append]
   constructor
   · rintro ⟨h, ⟨ys, zs, h₁, h₂⟩⟩
     refine ⟨h, ?_⟩
-    rw [join_eq_append_iff] at h₁
+    rw [flatten_eq_append_iff] at h₁
     obtain (⟨as, bs, rfl, rfl, h₁⟩ | ⟨as, bs, c, cs, ds, rfl, rfl, h₁⟩) := h₁
     · replace h₁ := h₁.symm
-      rw [join_eq_cons_iff] at h₁
+      rw [flatten_eq_cons_iff] at h₁
       obtain ⟨bs, cs, ds, rfl, h₁, rfl⟩ := h₁
       refine ⟨as ++ bs, [], cs, ds, by simp, ?_⟩
       simp
@@ -371,21 +376,25 @@ theorem find?_join_eq_some {xs : List (List α)} {p : α → Bool} {a : α} :
       · intro x m
         simpa using h₂ x (by simpa using .inr m)
   · rintro ⟨h, ⟨as, ys, zs, bs, rfl, h₁, h₂⟩⟩
-    refine ⟨h, as.join ++ ys, zs ++ bs.join, by simp, ?_⟩
+    refine ⟨h, as.flatten ++ ys, zs ++ bs.flatten, by simp, ?_⟩
     intro a m
     simp at m
     obtain ⟨l, ml, m⟩ | m := m
     · exact h₁ l ml a m
     · exact h₂ a m
 
-@[simp] theorem find?_bind (xs : List α) (f : α → List β) (p : β → Bool) :
-    (xs.bind f).find? p = xs.findSome? (fun x => (f x).find? p) := by
-  simp [bind_def, findSome?_map]; rfl
+@[simp] theorem find?_flatMap (xs : List α) (f : α → List β) (p : β → Bool) :
+    (xs.flatMap f).find? p = xs.findSome? (fun x => (f x).find? p) := by
+  simp [flatMap_def, findSome?_map]; rfl
 
-theorem find?_bind_eq_none {xs : List α} {f : α → List β} {p : β → Bool} :
-    (xs.bind f).find? p = none ↔ ∀ x ∈ xs, ∀ y ∈ f x, !p y := by
+@[deprecated find?_flatMap (since := "2024-10-16")] abbrev find?_bind := @find?_flatMap
+
+theorem find?_flatMap_eq_none {xs : List α} {f : α → List β} {p : β → Bool} :
+    (xs.flatMap f).find? p = none ↔ ∀ x ∈ xs, ∀ y ∈ f x, !p y := by
   simp
 
+@[deprecated find?_flatMap_eq_none (since := "2024-10-16")] abbrev find?_bind_eq_none := @find?_flatMap_eq_none
+
 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
@@ -432,7 +441,7 @@ theorem IsPrefix.find?_eq_some {l₁ l₂ : List α} {p : α → Bool} (h : l₁
     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]
+  simp +contextual [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 :=
@@ -558,7 +567,7 @@ theorem not_of_lt_findIdx {p : α → Bool} {xs : List α} {i : Nat} (h : i < xs
     | 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]
+      simp +singlePass only [← ipm, getElem_cons_succ]
       rw [← ipm, Nat.succ_lt_succ_iff] at h
       simpa using ih h
 
@@ -591,15 +600,14 @@ theorem findIdx_eq {p : α → Bool} {xs : List α} {i : Nat} (h : i < xs.length
 
 theorem findIdx_append (p : α → Bool) (l₁ l₂ : List α) :
     (l₁ ++ l₂).findIdx p =
-      if ∃ x, x ∈ l₁ ∧ p x = true then l₁.findIdx p else l₂.findIdx p + l₁.length := by
+      if l₁.findIdx p < l₁.length then l₁.findIdx p else l₂.findIdx p + l₁.length := by
   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]
+    · simp only [h, ih, cond_eq_if, Bool.false_eq_true, ↓reduceIte, add_one_lt_add_one_iff]
       split <;> simp [Nat.add_assoc]
 
 theorem IsPrefix.findIdx_le {l₁ l₂ : List α} {p : α → Bool} (h : l₁ <+: l₂) :
@@ -786,15 +794,15 @@ theorem findIdx?_of_eq_none {xs : List α} {p : α → Bool} (w : xs.findIdx? p
   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 =
+theorem findIdx?_flatten {l : List (List α)} {p : α → Bool} :
+    l.flatten.findIdx? p =
       (l.findIdx? (·.any p)).map
-        fun i => Nat.sum ((l.take i).map List.length) +
+        fun i => ((l.take i).map List.length).sum +
           (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,
+    simp only [flatten, 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,
@@ -976,4 +984,13 @@ theorem IsInfix.lookup_eq_none {l₁ l₂ : List (α × β)} (h : l₁ <:+: l₂
 
 end lookup
 
+/-! ### Deprecations -/
+
+@[deprecated head_flatten (since := "2024-10-14")] abbrev head_join := @head_flatten
+@[deprecated getLast_flatten (since := "2024-10-14")] abbrev getLast_join := @getLast_flatten
+@[deprecated find?_flatten (since := "2024-10-14")] abbrev find?_join := @find?_flatten
+@[deprecated find?_flatten_eq_none (since := "2024-10-14")] abbrev find?_join_eq_none := @find?_flatten_eq_none
+@[deprecated find?_flatten_eq_some (since := "2024-10-14")] abbrev find?_join_eq_some := @find?_flatten_eq_some
+@[deprecated findIdx?_flatten (since := "2024-10-14")] abbrev findIdx?_join := @findIdx?_flatten
+
 end List

src/Init/Data/List/Impl.lean

@@ -23,7 +23,7 @@ namespace List
 The following operations are already tail-recursive, and do not need `@[csimp]` replacements:
 `get`, `foldl`, `beq`, `isEqv`, `reverse`, `elem` (and hence `contains`), `drop`, `dropWhile`,
 `partition`, `isPrefixOf`, `isPrefixOf?`, `find?`, `findSome?`, `lookup`, `any` (and hence `or`),
-`all` (and hence `and`) , `range`, `eraseDups`, `eraseReps`, `span`, `groupBy`.
+`all` (and hence `and`) , `range`, `eraseDups`, `eraseReps`, `span`, `splitBy`.
 
 The following operations are still missing `@[csimp]` replacements:
 `concat`, `zipWithAll`.
@@ -31,14 +31,14 @@ The following operations are still missing `@[csimp]` replacements:
 The following operations are not recursive to begin with
 (or are defined in terms of recursive primitives):
 `isEmpty`, `isSuffixOf`, `isSuffixOf?`, `rotateLeft`, `rotateRight`, `insert`, `zip`, `enum`,
-`minimum?`, `maximum?`, and `removeAll`.
+`min?`, `max?`, and `removeAll`.
 
 The following operations were already given `@[csimp]` replacements in `Init/Data/List/Basic.lean`:
 `length`, `map`, `filter`, `replicate`, `leftPad`, `unzip`, `range'`, `iota`, `intersperse`.
 
 The following operations are given `@[csimp]` replacements below:
 `set`, `filterMap`, `foldr`, `append`, `bind`, `join`,
-`take`, `takeWhile`, `dropLast`, `replace`, `erase`, `eraseIdx`, `zipWith`,
+`take`, `takeWhile`, `dropLast`, `replace`, `modify`, `insertIdx`, `erase`, `eraseIdx`, `zipWith`,
 `enumFrom`, and `intercalate`.
 
 -/
@@ -93,29 +93,29 @@ The following operations are given `@[csimp]` replacements below:
 @[csimp] theorem foldr_eq_foldrTR : @foldr = @foldrTR := by
   funext α β f init l; simp [foldrTR, Array.foldr_eq_foldr_toList, -Array.size_toArray]
 
-/-! ### bind  -/
+/-! ### flatMap  -/
 
-/-- Tail recursive version of `List.bind`. -/
-@[inline] def bindTR (as : List α) (f : α → List β) : List β := go as #[] where
-  /-- Auxiliary for `bind`: `bind.go f as = acc.toList ++ bind f as` -/
+/-- Tail recursive version of `List.flatMap`. -/
+@[inline] def flatMapTR (as : List α) (f : α → List β) : List β := go as #[] where
+  /-- Auxiliary for `flatMap`: `flatMap.go f as = acc.toList ++ bind f as` -/
   @[specialize] go : List α → Array β → List β
   | [], acc => acc.toList
   | x::xs, acc => go xs (acc ++ f x)
 
-@[csimp] theorem bind_eq_bindTR : @List.bind = @bindTR := by
+@[csimp] theorem flatMap_eq_flatMapTR : @List.flatMap = @flatMapTR := by
   funext α β as f
-  let rec go : ∀ as acc, bindTR.go f as acc = acc.toList ++ as.bind f
-    | [], acc => by simp [bindTR.go, bind]
-    | x::xs, acc => by simp [bindTR.go, bind, go xs]
+  let rec go : ∀ as acc, flatMapTR.go f as acc = acc.toList ++ as.flatMap f
+    | [], acc => by simp [flatMapTR.go, flatMap]
+    | x::xs, acc => by simp [flatMapTR.go, flatMap, go xs]
   exact (go as #[]).symm
 
-/-! ### join -/
+/-! ### flatten -/
 
-/-- Tail recursive version of `List.join`. -/
-@[inline] def joinTR (l : List (List α)) : List α := bindTR l id
+/-- Tail recursive version of `List.flatten`. -/
+@[inline] def flattenTR (l : List (List α)) : List α := flatMapTR l id
 
-@[csimp] theorem join_eq_joinTR : @join = @joinTR := by
-  funext α l; rw [← List.bind_id, List.bind_eq_bindTR]; rfl
+@[csimp] theorem flatten_eq_flattenTR : @flatten = @flattenTR := by
+  funext α l; rw [← List.flatMap_id, List.flatMap_eq_flatMapTR]; rfl
 
 /-! ## Sublists -/
 
@@ -197,6 +197,41 @@ The following operations are given `@[csimp]` replacements below:
     · simp [*]
     · intro h; rw [IH] <;> simp_all
 
+/-! ### modify -/
+
+/-- Tail-recursive version of `modify`. -/
+def modifyTR (f : α → α) (n : Nat) (l : List α) : List α := go l n #[] where
+  /-- Auxiliary for `modifyTR`: `modifyTR.go f l n acc = acc.toList ++ modify f n l`. -/
+  go : List α → Nat → Array α → List α
+  | [], _, acc => acc.toList
+  | a :: l, 0, acc => acc.toListAppend (f a :: l)
+  | a :: l, n+1, acc => go l n (acc.push a)
+
+theorem modifyTR_go_eq : ∀ l n, modifyTR.go f l n acc = acc.toList ++ modify f n l
+  | [], n => by cases n <;> simp [modifyTR.go, modify]
+  | a :: l, 0 => by simp [modifyTR.go, modify]
+  | a :: l, n+1 => by simp [modifyTR.go, modify, modifyTR_go_eq l]
+
+@[csimp] theorem modify_eq_modifyTR : @modify = @modifyTR := by
+  funext α f n l; simp [modifyTR, modifyTR_go_eq]
+
+/-! ### insertIdx -/
+
+/-- Tail-recursive version of `insertIdx`. -/
+@[inline] def insertIdxTR (n : Nat) (a : α) (l : List α) : List α := go n l #[] where
+  /-- Auxiliary for `insertIdxTR`: `insertIdxTR.go a n l acc = acc.toList ++ insertIdx n a l`. -/
+  go : Nat → List α → Array α → List α
+  | 0, l, acc => acc.toListAppend (a :: l)
+  | _, [], acc => acc.toList
+  | n+1, a :: l, acc => go n l (acc.push a)
+
+theorem insertIdxTR_go_eq : ∀ n l, insertIdxTR.go a n l acc = acc.toList ++ insertIdx n a l
+  | 0, l | _+1, [] => by simp [insertIdxTR.go, insertIdx]
+  | n+1, a :: l => by simp [insertIdxTR.go, insertIdx, insertIdxTR_go_eq n l]
+
+@[csimp] theorem insertIdx_eq_insertIdxTR : @insertIdx = @insertIdxTR := by
+  funext α f n l; simp [insertIdxTR, insertIdxTR_go_eq]
+
 /-! ### erase -/
 
 /-- Tail recursive version of `List.erase`. -/
@@ -322,7 +357,7 @@ where
   | [_] => simp
   | x::y::xs =>
     let rec go {acc x} : ∀ xs,
-      intercalateTR.go sep.toArray x xs acc = acc.toList ++ join (intersperse sep (x::xs))
+      intercalateTR.go sep.toArray x xs acc = acc.toList ++ flatten (intersperse sep (x::xs))
     | [] => by simp [intercalateTR.go]
     | _::_ => by simp [intercalateTR.go, go]
     simp [intersperse, go]

src/Init/Data/List/Lemmas.lean

@@ -55,7 +55,7 @@ See also
 * `Init.Data.List.Erase` for lemmas about `List.eraseP` and `List.erase`.
 * `Init.Data.List.Find` for lemmas about `List.find?`, `List.findSome?`, `List.findIdx`,
   `List.findIdx?`, and `List.indexOf`
-* `Init.Data.List.MinMax` for lemmas about `List.minimum?` and `List.maximum?`.
+* `Init.Data.List.MinMax` for lemmas about `List.min?` and `List.max?`.
 * `Init.Data.List.Pairwise` for lemmas about `List.Pairwise` and `List.Nodup`.
 * `Init.Data.List.Sublist` for lemmas about `List.Subset`, `List.Sublist`, `List.IsPrefix`,
   `List.IsSuffix`, and `List.IsInfix`.
@@ -191,7 +191,7 @@ theorem get?_eq_some : l.get? n = some a ↔ ∃ h, get l ⟨n, h⟩ = a :=
   ⟨fun e =>
     have : n < length l := Nat.gt_of_not_le fun hn => by cases get?_len_le hn ▸ e
     ⟨this, by rwa [get?_eq_get this, Option.some.injEq] at e⟩,
-  fun ⟨h, e⟩ => e ▸ get?_eq_get _⟩
+  fun ⟨_, e⟩ => e ▸ get?_eq_get _⟩
 
 theorem get?_eq_none : l.get? n = none ↔ length l ≤ n :=
   ⟨fun e => Nat.ge_of_not_lt (fun h' => by cases e ▸ get?_eq_some.2 ⟨h', rfl⟩), get?_len_le⟩
@@ -203,6 +203,9 @@ theorem get?_eq_none : l.get? n = none ↔ length l ≤ n :=
 
 @[simp] theorem get_eq_getElem (l : List α) (i : Fin l.length) : l.get i = l[i.1]'i.2 := rfl
 
+theorem getElem?_eq_some {l : List α} : l[i]? = some a ↔ ∃ h : i < l.length, l[i]'h = a := by
+  simpa using get?_eq_some
+
 /--
 If one has `l.get i` in an expression (with `i : Fin l.length`) and `h : l = l'`,
 `rw [h]` will give a "motive it not type correct" error, as it cannot rewrite the
@@ -489,10 +492,6 @@ theorem getElem?_of_mem {a} {l : List α} (h : a ∈ l) : ∃ n : Nat, l[n]? = s
 theorem get?_of_mem {a} {l : List α} (h : a ∈ l) : ∃ n, l.get? n = some a :=
   let ⟨⟨n, _⟩, e⟩ := get_of_mem h; ⟨n, e ▸ get?_eq_get _⟩
 
-theorem getElem_mem : ∀ {l : List α} {n} (h : n < l.length), l[n]'h ∈ l
-  | _ :: _, 0, _ => .head ..
-  | _ :: l, _+1, _ => .tail _ (getElem_mem (l := l) ..)
-
 theorem get_mem : ∀ (l : List α) n h, get l ⟨n, h⟩ ∈ l
   | _ :: _, 0, _ => .head ..
   | _ :: l, _+1, _ => .tail _ (get_mem l ..)
@@ -715,9 +714,9 @@ theorem set_eq_of_length_le {l : List α} {n : Nat} (h : l.length ≤ n) {a : α
 theorem set_comm (a b : α) : ∀ {n m : Nat} (l : List α), n ≠ m →
     (l.set n a).set m b = (l.set m b).set n a
   | _, _, [], _ => by simp
-  | n+1, 0, _ :: _, _ => by simp [set]
-  | 0, m+1, _ :: _, _ => by simp [set]
-  | n+1, m+1, x :: t, h =>
+  | _+1, 0, _ :: _, _ => by simp [set]
+  | 0, _+1, _ :: _, _ => by simp [set]
+  | _+1, _+1, _ :: t, h =>
     congrArg _ <| set_comm a b t fun h' => h <| Nat.succ_inj'.mpr h'
 
 @[simp]
@@ -864,20 +863,50 @@ theorem foldr_map (f : α₁ → α₂) (g : α₂ → β → β) (l : List α
     (l.map f).foldr g init = l.foldr (fun x y => g (f x) y) init := by
   induction l generalizing init <;> simp [*]
 
-theorem foldl_map' {α β : Type u} (g : α → β) (f : α → α → α) (f' : β → β → β) (a : α) (l : List α)
+theorem foldl_filterMap (f : α → Option β) (g : γ → β → γ) (l : List α) (init : γ) :
+    (l.filterMap f).foldl g init = l.foldl (fun x y => match f y with | some b => g x b | none => x) init := by
+  induction l generalizing init with
+  | nil => rfl
+  | cons a l ih =>
+    simp only [filterMap_cons, foldl_cons]
+    cases f a <;> simp [ih]
+
+theorem foldr_filterMap (f : α → Option β) (g : β → γ → γ) (l : List α) (init : γ) :
+    (l.filterMap f).foldr g init = l.foldr (fun x y => match f x with | some b => g b y | none => y) init := by
+  induction l generalizing init with
+  | nil => rfl
+  | cons a l ih =>
+    simp only [filterMap_cons, foldr_cons]
+    cases f a <;> simp [ih]
+
+theorem foldl_map' (g : α → β) (f : α → α → α) (f' : β → β → β) (a : α) (l : List α)
     (h : ∀ x y, f' (g x) (g y) = g (f x y)) :
     (l.map g).foldl f' (g a) = g (l.foldl f a) := by
   induction l generalizing a
   · simp
   · simp [*, h]
 
-theorem foldr_map' {α β : Type u} (g : α → β) (f : α → α → α) (f' : β → β → β) (a : α) (l : List α)
+theorem foldr_map' (g : α → β) (f : α → α → α) (f' : β → β → β) (a : α) (l : List α)
     (h : ∀ x y, f' (g x) (g y) = g (f x y)) :
     (l.map g).foldr f' (g a) = g (l.foldr f a) := by
   induction l generalizing a
   · simp
   · simp [*, h]
 
+theorem foldl_assoc {op : α → α → α} [ha : Std.Associative op] :
+    ∀ {l : List α} {a₁ a₂}, l.foldl op (op a₁ a₂) = op a₁ (l.foldl op a₂)
+  | [], a₁, a₂ => rfl
+  | a :: l, a₁, a₂ => by
+    simp only [foldl_cons, ha.assoc]
+    rw [foldl_assoc]
+
+theorem foldr_assoc {op : α → α → α} [ha : Std.Associative op] :
+    ∀ {l : List α} {a₁ a₂}, l.foldr op (op a₁ a₂) = op (l.foldr op a₁) a₂
+  | [], a₁, a₂ => rfl
+  | a :: l, a₁, a₂ => by
+    simp only [foldr_cons, ha.assoc]
+    rw [foldr_assoc]
+
 theorem foldl_hom (f : α₁ → α₂) (g₁ : α₁ → β → α₁) (g₂ : α₂ → β → α₂) (l : List β) (init : α₁)
     (H : ∀ x y, g₂ (f x) y = f (g₁ x y)) : l.foldl g₂ (f init) = f (l.foldl g₁ init) := by
   induction l generalizing init <;> simp [*, H]
@@ -970,6 +999,21 @@ theorem foldr_rel {l : List α} {f g : α → β → β} {a b : β} (r : β →
     · simp
     · exact ih h fun a m c c' h => h' _ (by simp_all) _ _ h
 
+@[simp] theorem foldl_add_const (l : List α) (a b : Nat) :
+    l.foldl (fun x _ => x + a) b = b + a * l.length := by
+  induction l generalizing b with
+  | nil => simp
+  | cons y l ih =>
+    simp only [foldl_cons, ih, length_cons, Nat.mul_add, Nat.mul_one, Nat.add_assoc,
+      Nat.add_comm a]
+
+@[simp] theorem foldr_add_const (l : List α) (a b : Nat) :
+    l.foldr (fun _ x => x + a) b = b + a * l.length := by
+  induction l generalizing b with
+  | nil => simp
+  | cons y l ih =>
+    simp only [foldr_cons, ih, length_cons, Nat.mul_add, Nat.mul_one, Nat.add_assoc]
+
 /-! ### getLast -/
 
 theorem getLast_eq_getElem : ∀ (l : List α) (h : l ≠ []),
@@ -977,8 +1021,8 @@ theorem getLast_eq_getElem : ∀ (l : List α) (h : l ≠ []),
       match l with
       | [] => contradiction
       | a :: l => exact Nat.le_refl _)
-  | [a], h => rfl
-  | a :: b :: l, h => by
+  | [_], _ => rfl
+  | _ :: _ :: _, _ => by
     simp [getLast, get, Nat.succ_sub_succ, getLast_eq_getElem]
 
 @[deprecated getLast_eq_getElem (since := "2024-07-15")]
@@ -1001,17 +1045,17 @@ theorem getLast_eq_getLastD (a l h) : @getLast α (a::l) h = getLastD l a := by
 
 @[simp] theorem getLast_singleton (a h) : @getLast α [a] h = a := rfl
 
-theorem getLast!_cons [Inhabited α] : @getLast! α _ (a::l) = getLastD l a := by
+theorem getLast!_cons_eq_getLastD [Inhabited α] : @getLast! α _ (a::l) = getLastD l a := by
   simp [getLast!, getLast_eq_getLastD]
 
-theorem getLast_mem : ∀ {l : List α} (h : l ≠ []), getLast l h ∈ l
+@[simp] theorem getLast_mem : ∀ {l : List α} (h : l ≠ []), getLast l h ∈ l
   | [], h => absurd rfl h
   | [_], _ => .head ..
   | _::a::l, _ => .tail _ <| getLast_mem (cons_ne_nil a l)
 
 theorem getLast_mem_getLast? : ∀ {l : List α} (h : l ≠ []), getLast l h ∈ getLast? l
   | [], h => by contradiction
-  | a :: l, _ => rfl
+  | _ :: _, _ => rfl
 
 theorem getLastD_mem_cons : ∀ (l : List α) (a : α), getLastD l a ∈ a::l
   | [], _ => .head ..
@@ -1030,9 +1074,6 @@ theorem get_cons_length (x : α) (xs : List α) (n : Nat) (h : n = xs.length) :
 
 @[simp] theorem getLast?_singleton (a : α) : getLast? [a] = a := rfl
 
-theorem getLast!_of_getLast? [Inhabited α] : ∀ {l : List α}, getLast? l = some a → getLast! l = a
-  | _ :: _, rfl => rfl
-
 theorem getLast?_eq_getLast : ∀ l h, @getLast? α l = some (getLast l h)
   | [], h => nomatch h rfl
   | _ :: _, _ => rfl
@@ -1066,6 +1107,26 @@ theorem getLast?_concat (l : List α) : getLast? (l ++ [a]) = some a := by
 theorem getLastD_concat (a b l) : @getLastD α (l ++ [b]) a = b := by
   rw [getLastD_eq_getLast?, getLast?_concat]; rfl
 
+/-! ### getLast! -/
+
+theorem getLast!_nil [Inhabited α] : ([] : List α).getLast! = default := rfl
+
+@[simp] theorem getLast!_eq_getLast?_getD [Inhabited α] {l : List α} : getLast! l = (getLast? l).getD default := by
+  cases l with
+  | nil => simp [getLast!_nil]
+  | cons _ _ => simp [getLast!, getLast?_eq_getLast]
+
+theorem getLast!_of_getLast? [Inhabited α] : ∀ {l : List α}, getLast? l = some a → getLast! l = a
+  | _ :: _, rfl => rfl
+
+theorem getLast!_eq_getElem! [Inhabited α] {l : List α} : l.getLast! = l[l.length - 1]! := by
+  cases l with
+  | nil => simp
+  | cons _ _ =>
+    apply getLast!_of_getLast?
+    rw [getElem!_pos, getElem_cons_length (h := by simp)]
+    rfl
+
 /-! ## Head and tail -/
 
 /-! ### head -/
@@ -1102,7 +1163,7 @@ theorem head?_eq_some_iff {xs : List α} {a : α} : xs.head? = some a ↔ ∃ ys
 @[simp] theorem head?_isSome : l.head?.isSome ↔ l ≠ [] := by
   cases l <;> simp
 
-theorem head_mem : ∀ {l : List α} (h : l ≠ []), head l h ∈ l
+@[simp] theorem head_mem : ∀ {l : List α} (h : l ≠ []), head l h ∈ l
   | [], h => absurd rfl h
   | _::_, _ => .head ..
 
@@ -1117,7 +1178,7 @@ theorem mem_of_mem_head? : ∀ {l : List α} {a : α}, a ∈ l.head? → a ∈ l
 
 theorem head_mem_head? : ∀ {l : List α} (h : l ≠ []), head l h ∈ head? l
   | [], h => by contradiction
-  | a :: l, _ => rfl
+  | _ :: _, _ => rfl
 
 theorem head?_concat {a : α} : (l ++ [a]).head? = l.head?.getD a := by
   cases l <;> simp
@@ -1326,12 +1387,12 @@ theorem set_map {f : α → β} {l : List α} {n : Nat} {a : α} :
   simp
 
 @[simp] theorem head_map (f : α → β) (l : List α) (w) :
-    head (map f l) w = f (head l (by simpa using w)) := by
+    (map f l).head w = f (l.head (by simpa using w)) := by
   cases l
   · simp at w
   · simp_all
 
-@[simp] theorem head?_map (f : α → β) (l : List α) : head? (map f l) = (head? l).map f := by
+@[simp] theorem head?_map (f : α → β) (l : List α) : (map f l).head? = l.head?.map f := by
   cases l <;> rfl
 
 @[simp] theorem map_tail? (f : α → β) (l : List α) : (tail? l).map (map f) = tail? (map f l) := by
@@ -1432,6 +1493,22 @@ theorem forall_mem_filter {l : List α} {p : α → Bool} {P : α → Prop} :
   | [] => rfl
   | a :: l => by by_cases hp : p a <;> by_cases hq : q a <;> simp [hp, hq, filter_filter _ l]
 
+theorem foldl_filter (p : α → Bool) (f : β → α → β) (l : List α) (init : β) :
+    (l.filter p).foldl f init = l.foldl (fun x y => if p y then f x y else x) init := by
+  induction l generalizing init with
+  | nil => rfl
+  | cons a l ih =>
+    simp only [filter_cons, foldl_cons]
+    split <;> simp [ih]
+
+theorem foldr_filter (p : α → Bool) (f : α → β → β) (l : List α) (init : β) :
+    (l.filter p).foldr f init = l.foldr (fun x y => if p x then f x y else y) init := by
+  induction l generalizing init with
+  | nil => rfl
+  | cons a l ih =>
+    simp only [filter_cons, foldr_cons]
+    split <;> simp [ih]
+
 theorem filter_map (f : β → α) (l : List β) : filter p (map f l) = map f (filter (p ∘ f) l) := by
   induction l with
   | nil => rfl
@@ -1449,7 +1526,7 @@ theorem map_filter_eq_foldr (f : α → β) (p : α → Bool) (as : List α) :
 
 @[simp] theorem filter_append {p : α → Bool} :
     ∀ (l₁ l₂ : List α), filter p (l₁ ++ l₂) = filter p l₁ ++ filter p l₂
-  | [], l₂ => rfl
+  | [], _ => rfl
   | a :: l₁, l₂ => by simp [filter]; split <;> simp [filter_append l₁]
 
 theorem filter_eq_cons_iff {l} {a} {as} :
@@ -1654,6 +1731,11 @@ theorem filterMap_eq_cons_iff {l} {b} {bs} :
 
 /-! ### append -/
 
+@[simp] theorem nil_append_fun : (([] : List α) ++ ·) = id := rfl
+
+@[simp] theorem cons_append_fun (a : α) (as : List α) :
+    (fun bs => ((a :: as) ++ bs)) = fun bs => a :: (as ++ bs) := rfl
+
 theorem getElem_append {l₁ l₂ : List α} (n : Nat) (h) :
     (l₁ ++ l₂)[n] = if h' : n < l₁.length then l₁[n] else l₂[n - l₁.length]'(by simp at h h'; exact Nat.sub_lt_left_of_lt_add h' h) := by
   split <;> rename_i h'
@@ -1668,7 +1750,7 @@ theorem getElem?_append_left {l₁ l₂ : List α} {n : Nat} (hn : n < l₁.leng
 
 theorem getElem?_append_right : ∀ {l₁ l₂ : List α} {n : Nat}, l₁.length ≤ n →
   (l₁ ++ l₂)[n]? = l₂[n - l₁.length]?
-| [], _, n, _ => rfl
+| [], _, _, _ => rfl
 | a :: l, _, n+1, h₁ => by
   rw [cons_append]
   simp [Nat.succ_sub_succ_eq_sub, getElem?_append_right (Nat.lt_succ.1 h₁)]
@@ -1733,8 +1815,8 @@ theorem append_of_mem {a : α} {l : List α} : a ∈ l → ∃ s t : List α, l
 
 theorem append_inj :
     ∀ {s₁ s₂ t₁ t₂ : List α}, s₁ ++ t₁ = s₂ ++ t₂ → length s₁ = length s₂ → s₁ = s₂ ∧ t₁ = t₂
-  | [], [], t₁, t₂, h, _ => ⟨rfl, h⟩
-  | a :: s₁, b :: s₂, t₁, t₂, h, hl => by
+  | [], [], _, _, h, _ => ⟨rfl, h⟩
+  | _ :: _, _ :: _, _, _, h, hl => by
     simp [append_inj (cons.inj h).2 (Nat.succ.inj hl)] at h ⊢; exact h
 
 theorem append_inj_right (h : s₁ ++ t₁ = s₂ ++ t₂) (hl : length s₁ = length s₂) : t₁ = t₂ :=
@@ -2046,106 +2128,97 @@ theorem eq_nil_or_concat : ∀ l : List α, l = [] ∨ ∃ L b, l = concat L b
     | _, .inl rfl => .inr ⟨[], a, rfl⟩
     | _, .inr ⟨L, b, rfl⟩ => .inr ⟨a::L, b, rfl⟩
 
-/-! ### join -/
+/-! ### flatten -/
 
-@[simp] theorem length_join (L : List (List α)) : (join L).length = Nat.sum (L.map length) := by
+@[simp] theorem length_flatten (L : List (List α)) : (flatten L).length = (L.map length).sum := by
   induction L with
   | nil => rfl
   | cons =>
-    simp [join, length_append, *]
+    simp [flatten, length_append, *]
 
-theorem join_singleton (l : List α) : [l].join = l := by simp
+theorem flatten_singleton (l : List α) : [l].flatten = l := by simp
 
-@[simp] theorem mem_join : ∀ {L : List (List α)}, a ∈ L.join ↔ ∃ l, l ∈ L ∧ a ∈ l
+@[simp] theorem mem_flatten : ∀ {L : List (List α)}, a ∈ L.flatten ↔ ∃ l, l ∈ L ∧ a ∈ l
   | [] => by simp
-  | b :: l => by simp [mem_join, or_and_right, exists_or]
+  | b :: l => by simp [mem_flatten, or_and_right, exists_or]
 
-@[simp] theorem join_eq_nil_iff {L : List (List α)} : L.join = [] ↔ ∀ l ∈ L, l = [] := by
+@[simp] theorem flatten_eq_nil_iff {L : List (List α)} : L.flatten = [] ↔ ∀ l ∈ L, l = [] := by
   induction L <;> simp_all
 
-@[deprecated join_eq_nil_iff (since := "2024-09-05")] abbrev join_eq_nil := @join_eq_nil_iff
-
-theorem join_ne_nil_iff {xs : List (List α)} : xs.join ≠ [] ↔ ∃ x, x ∈ xs ∧ x ≠ [] := by
+theorem flatten_ne_nil_iff {xs : List (List α)} : xs.flatten ≠ [] ↔ ∃ x, x ∈ xs ∧ x ≠ [] := by
   simp
 
-@[deprecated join_ne_nil_iff (since := "2024-09-05")] abbrev join_ne_nil := @join_ne_nil_iff
+theorem exists_of_mem_flatten : a ∈ flatten L → ∃ l, l ∈ L ∧ a ∈ l := mem_flatten.1
 
-theorem exists_of_mem_join : a ∈ join L → ∃ l, l ∈ L ∧ a ∈ l := mem_join.1
+theorem mem_flatten_of_mem (lL : l ∈ L) (al : a ∈ l) : a ∈ flatten L := mem_flatten.2 ⟨l, lL, al⟩
 
-theorem mem_join_of_mem (lL : l ∈ L) (al : a ∈ l) : a ∈ join L := mem_join.2 ⟨l, lL, al⟩
-
-theorem forall_mem_join {p : α → Prop} {L : List (List α)} :
-    (∀ (x) (_ : x ∈ join L), p x) ↔ ∀ (l) (_ : l ∈ L) (x) (_ : x ∈ l), p x := by
-  simp only [mem_join, forall_exists_index, and_imp]
+theorem forall_mem_flatten {p : α → Prop} {L : List (List α)} :
+    (∀ (x) (_ : x ∈ flatten L), p x) ↔ ∀ (l) (_ : l ∈ L) (x) (_ : x ∈ l), p x := by
+  simp only [mem_flatten, forall_exists_index, and_imp]
   constructor <;> (intros; solve_by_elim)
 
-theorem join_eq_bind {L : List (List α)} : join L = L.bind id := by
-  induction L <;> simp [List.bind]
+theorem flatten_eq_flatMap {L : List (List α)} : flatten L = L.flatMap id := by
+  induction L <;> simp [List.flatMap]
 
-theorem head?_join {L : List (List α)} : (join L).head? = L.findSome? fun l => l.head? := by
+theorem head?_flatten {L : List (List α)} : (flatten L).head? = L.findSome? fun l => l.head? := by
   induction L with
   | nil => rfl
   | cons =>
     simp only [findSome?_cons]
     split <;> simp_all
 
--- `getLast?_join` is proved later, after the `reverse` section.
--- `head_join` and `getLast_join` are proved in `Init.Data.List.Find`.
+-- `getLast?_flatten` is proved later, after the `reverse` section.
+-- `head_flatten` and `getLast_flatten` are proved in `Init.Data.List.Find`.
 
-theorem foldl_join (f : β → α → β) (b : β) (L : List (List α)) :
-    (join L).foldl f b = L.foldl (fun b l => l.foldl f b) b := by
+theorem foldl_flatten (f : β → α → β) (b : β) (L : List (List α)) :
+    (flatten L).foldl f b = L.foldl (fun b l => l.foldl f b) b := by
   induction L generalizing b <;> simp_all
 
-theorem foldr_join (f : α → β → β) (b : β) (L : List (List α)) :
-    (join L).foldr f b = L.foldr (fun l b => l.foldr f b) b := by
+theorem foldr_flatten (f : α → β → β) (b : β) (L : List (List α)) :
+    (flatten L).foldr f b = L.foldr (fun l b => l.foldr f b) b := by
   induction L <;> simp_all
 
-@[simp] theorem map_join (f : α → β) (L : List (List α)) : map f (join L) = join (map (map f) L) := by
+@[simp] theorem map_flatten (f : α → β) (L : List (List α)) : map f (flatten L) = flatten (map (map f) L) := by
   induction L <;> simp_all
 
-@[simp] theorem filterMap_join (f : α → Option β) (L : List (List α)) :
-    filterMap f (join L) = join (map (filterMap f) L) := by
+@[simp] theorem filterMap_flatten (f : α → Option β) (L : List (List α)) :
+    filterMap f (flatten L) = flatten (map (filterMap f) L) := by
   induction L <;> simp [*, filterMap_append]
 
-@[simp] theorem filter_join (p : α → Bool) (L : List (List α)) :
-    filter p (join L) = join (map (filter p) L) := by
+@[simp] theorem filter_flatten (p : α → Bool) (L : List (List α)) :
+    filter p (flatten L) = flatten (map (filter p) L) := by
   induction L <;> simp [*, filter_append]
 
-theorem join_filter_not_isEmpty  :
-    ∀ {L : List (List α)}, join (L.filter fun l => !l.isEmpty) = L.join
+theorem flatten_filter_not_isEmpty  :
+    ∀ {L : List (List α)}, flatten (L.filter fun l => !l.isEmpty) = L.flatten
   | [] => rfl
   | [] :: L
   | (a :: l) :: L => by
-      simp [join_filter_not_isEmpty (L := L)]
+      simp [flatten_filter_not_isEmpty (L := L)]
 
-theorem join_filter_ne_nil [DecidablePred fun l : List α => l ≠ []] {L : List (List α)} :
-    join (L.filter fun l => l ≠ []) = L.join := by
+theorem flatten_filter_ne_nil [DecidablePred fun l : List α => l ≠ []] {L : List (List α)} :
+    flatten (L.filter fun l => l ≠ []) = L.flatten := by
   simp only [ne_eq, ← isEmpty_iff, Bool.not_eq_true, Bool.decide_eq_false,
-    join_filter_not_isEmpty]
+    flatten_filter_not_isEmpty]
 
-@[deprecated filter_join (since := "2024-08-26")]
-theorem join_map_filter (p : α → Bool) (l : List (List α)) :
-    (l.map (filter p)).join = (l.join).filter p := by
-  rw [filter_join]
-
-@[simp] theorem join_append (L₁ L₂ : List (List α)) : join (L₁ ++ L₂) = join L₁ ++ join L₂ := by
+@[simp] theorem flatten_append (L₁ L₂ : List (List α)) : flatten (L₁ ++ L₂) = flatten L₁ ++ flatten L₂ := by
   induction L₁ <;> simp_all
 
-theorem join_concat (L : List (List α)) (l : List α) : join (L ++ [l]) = join L ++ l := by
+theorem flatten_concat (L : List (List α)) (l : List α) : flatten (L ++ [l]) = flatten L ++ l := by
   simp
 
-theorem join_join {L : List (List (List α))} : join (join L) = join (map join L) := by
+theorem flatten_flatten {L : List (List (List α))} : flatten (flatten L) = flatten (map flatten L) := by
   induction L <;> simp_all
 
-theorem join_eq_cons_iff {xs : List (List α)} {y : α} {ys : List α} :
-    xs.join = y :: ys ↔
-      ∃ as bs cs, xs = as ++ (y :: bs) :: cs ∧ (∀ l, l ∈ as → l = []) ∧ ys = bs ++ cs.join := by
+theorem flatten_eq_cons_iff {xs : List (List α)} {y : α} {ys : List α} :
+    xs.flatten = y :: ys ↔
+      ∃ as bs cs, xs = as ++ (y :: bs) :: cs ∧ (∀ l, l ∈ as → l = []) ∧ ys = bs ++ cs.flatten := by
   constructor
   · induction xs with
     | nil => simp
     | cons x xs ih =>
       intro h
-      simp only [join_cons] at h
+      simp only [flatten_cons] at h
       replace h := h.symm
       rw [cons_eq_append_iff] at h
       obtain (⟨rfl, h⟩ | ⟨z⟩) := h
@@ -2156,23 +2229,23 @@ theorem join_eq_cons_iff {xs : List (List α)} {y : α} {ys : List α} :
         refine ⟨[], a', xs, ?_⟩
         simp
   · rintro ⟨as, bs, cs, rfl, h₁, rfl⟩
-    simp [join_eq_nil_iff.mpr h₁]
+    simp [flatten_eq_nil_iff.mpr h₁]
 
-theorem join_eq_append_iff {xs : List (List α)} {ys zs : List α} :
-    xs.join = ys ++ zs ↔
-      (∃ as bs, xs = as ++ bs ∧ ys = as.join ∧ zs = bs.join) ∨
-        ∃ as bs c cs ds, xs = as ++ (bs ++ c :: cs) :: ds ∧ ys = as.join ++ bs ∧
-          zs = c :: cs ++ ds.join := by
+theorem flatten_eq_append_iff {xs : List (List α)} {ys zs : List α} :
+    xs.flatten = ys ++ zs ↔
+      (∃ as bs, xs = as ++ bs ∧ ys = as.flatten ∧ zs = bs.flatten) ∨
+        ∃ as bs c cs ds, xs = as ++ (bs ++ c :: cs) :: ds ∧ ys = as.flatten ++ bs ∧
+          zs = c :: cs ++ ds.flatten := by
   constructor
   · induction xs generalizing ys with
     | nil =>
-      simp only [join_nil, nil_eq, append_eq_nil, and_false, cons_append, false_and, exists_const,
+      simp only [flatten_nil, nil_eq, append_eq_nil, and_false, cons_append, false_and, exists_const,
         exists_false, or_false, and_imp, List.cons_ne_nil]
       rintro rfl rfl
       exact ⟨[], [], by simp⟩
     | cons x xs ih =>
       intro h
-      simp only [join_cons] at h
+      simp only [flatten_cons] at h
       rw [append_eq_append_iff] at h
       obtain (⟨ys, rfl, h⟩ | ⟨c', rfl, h⟩) := h
       · obtain (⟨as, bs, rfl, rfl, rfl⟩ | ⟨as, bs, c, cs, ds, rfl, rfl, rfl⟩) := ih h
@@ -2186,18 +2259,15 @@ theorem join_eq_append_iff {xs : List (List α)} {ys zs : List α} :
     · simp
     · simp
 
-@[deprecated join_eq_cons_iff (since := "2024-09-05")] abbrev join_eq_cons := @join_eq_cons_iff
-@[deprecated join_eq_append_iff (since := "2024-09-05")] abbrev join_eq_append := @join_eq_append_iff
-
-/-- Two lists of sublists are equal iff their joins coincide, as well as the lengths of the
+/-- Two lists of sublists are equal iff their flattens coincide, as well as the lengths of the
 sublists. -/
-theorem eq_iff_join_eq : ∀ {L L' : List (List α)},
-    L = L' ↔ L.join = L'.join ∧ map length L = map length L'
+theorem eq_iff_flatten_eq : ∀ {L L' : List (List α)},
+    L = L' ↔ L.flatten = L'.flatten ∧ map length L = map length L'
   | _, [] => by simp_all
   | [], x' :: L' => by simp_all
   | x :: L, x' :: L' => by
     simp
-    rw [eq_iff_join_eq]
+    rw [eq_iff_flatten_eq]
     constructor
     · rintro ⟨rfl, h₁, h₂⟩
       simp_all
@@ -2205,86 +2275,86 @@ theorem eq_iff_join_eq : ∀ {L L' : List (List α)},
       obtain ⟨rfl, h⟩ := append_inj h₁ h₂
       exact ⟨rfl, h, h₃⟩
 
-/-! ### bind -/
+/-! ### flatMap -/
 
-theorem bind_def (l : List α) (f : α → List β) : l.bind f = join (map f l) := by rfl
+theorem flatMap_def (l : List α) (f : α → List β) : l.flatMap f = flatten (map f l) := by rfl
 
-@[simp] theorem bind_id (l : List (List α)) : List.bind l id = l.join := by simp [bind_def]
+@[simp] theorem flatMap_id (l : List (List α)) : List.flatMap l id = l.flatten := by simp [flatMap_def]
 
-@[simp] theorem mem_bind {f : α → List β} {b} {l : List α} : b ∈ l.bind f ↔ ∃ a, a ∈ l ∧ b ∈ f a := by
-  simp [bind_def, mem_join]
+@[simp] theorem mem_flatMap {f : α → List β} {b} {l : List α} : b ∈ l.flatMap f ↔ ∃ a, a ∈ l ∧ b ∈ f a := by
+  simp [flatMap_def, mem_flatten]
   exact ⟨fun ⟨_, ⟨a, h₁, rfl⟩, h₂⟩ => ⟨a, h₁, h₂⟩, fun ⟨a, h₁, h₂⟩ => ⟨_, ⟨a, h₁, rfl⟩, h₂⟩⟩
 
-theorem exists_of_mem_bind {b : β} {l : List α} {f : α → List β} :
-    b ∈ l.bind f → ∃ a, a ∈ l ∧ b ∈ f a := mem_bind.1
+theorem exists_of_mem_flatMap {b : β} {l : List α} {f : α → List β} :
+    b ∈ l.flatMap f → ∃ a, a ∈ l ∧ b ∈ f a := mem_flatMap.1
 
-theorem mem_bind_of_mem {b : β} {l : List α} {f : α → List β} {a} (al : a ∈ l) (h : b ∈ f a) :
-    b ∈ l.bind f := mem_bind.2 ⟨a, al, h⟩
+theorem mem_flatMap_of_mem {b : β} {l : List α} {f : α → List β} {a} (al : a ∈ l) (h : b ∈ f a) :
+    b ∈ l.flatMap f := mem_flatMap.2 ⟨a, al, h⟩
 
 @[simp]
-theorem bind_eq_nil_iff {l : List α} {f : α → List β} : List.bind l f = [] ↔ ∀ x ∈ l, f x = [] :=
-  join_eq_nil_iff.trans <| by
+theorem flatMap_eq_nil_iff {l : List α} {f : α → List β} : List.flatMap l f = [] ↔ ∀ x ∈ l, f x = [] :=
+  flatten_eq_nil_iff.trans <| by
     simp only [mem_map, forall_exists_index, and_imp, forall_apply_eq_imp_iff₂]
 
-@[deprecated bind_eq_nil_iff (since := "2024-09-05")] abbrev bind_eq_nil := @bind_eq_nil_iff
+@[deprecated flatMap_eq_nil_iff (since := "2024-09-05")] abbrev bind_eq_nil := @flatMap_eq_nil_iff
 
-theorem forall_mem_bind {p : β → Prop} {l : List α} {f : α → List β} :
-    (∀ (x) (_ : x ∈ l.bind f), p x) ↔ ∀ (a) (_ : a ∈ l) (b) (_ : b ∈ f a), p b := by
-  simp only [mem_bind, forall_exists_index, and_imp]
+theorem forall_mem_flatMap {p : β → Prop} {l : List α} {f : α → List β} :
+    (∀ (x) (_ : x ∈ l.flatMap f), p x) ↔ ∀ (a) (_ : a ∈ l) (b) (_ : b ∈ f a), p b := by
+  simp only [mem_flatMap, forall_exists_index, and_imp]
   constructor <;> (intros; solve_by_elim)
 
-theorem bind_singleton (f : α → List β) (x : α) : [x].bind f = f x :=
+theorem flatMap_singleton (f : α → List β) (x : α) : [x].flatMap f = f x :=
   append_nil (f x)
 
-@[simp] theorem bind_singleton' (l : List α) : (l.bind fun x => [x]) = l := by
+@[simp] theorem flatMap_singleton' (l : List α) : (l.flatMap fun x => [x]) = l := by
   induction l <;> simp [*]
 
-theorem head?_bind {l : List α} {f : α → List β} :
-    (l.bind f).head? = l.findSome? fun a => (f a).head? := by
+theorem head?_flatMap {l : List α} {f : α → List β} :
+    (l.flatMap f).head? = l.findSome? fun a => (f a).head? := by
   induction l with
   | nil => rfl
   | cons =>
     simp only [findSome?_cons]
     split <;> simp_all
 
-@[simp] theorem bind_append (xs ys : List α) (f : α → List β) :
-    (xs ++ ys).bind f = xs.bind f ++ ys.bind f := by
-  induction xs; {rfl}; simp_all [bind_cons, append_assoc]
+@[simp] theorem flatMap_append (xs ys : List α) (f : α → List β) :
+    (xs ++ ys).flatMap f = xs.flatMap f ++ ys.flatMap f := by
+  induction xs; {rfl}; simp_all [flatMap_cons, append_assoc]
 
-@[deprecated bind_append (since := "2024-07-24")] abbrev append_bind := @bind_append
+@[deprecated flatMap_append (since := "2024-07-24")] abbrev append_bind := @flatMap_append
 
-theorem bind_assoc {α β} (l : List α) (f : α → List β) (g : β → List γ) :
-    (l.bind f).bind g = l.bind fun x => (f x).bind g := by
+theorem flatMap_assoc {α β} (l : List α) (f : α → List β) (g : β → List γ) :
+    (l.flatMap f).flatMap g = l.flatMap fun x => (f x).flatMap g := by
   induction l <;> simp [*]
 
-theorem map_bind (f : β → γ) (g : α → List β) :
-    ∀ l : List α, (l.bind g).map f = l.bind fun a => (g a).map f
+theorem map_flatMap (f : β → γ) (g : α → List β) :
+    ∀ l : List α, (l.flatMap g).map f = l.flatMap fun a => (g a).map f
   | [] => rfl
-  | a::l => by simp only [bind_cons, map_append, map_bind _ _ l]
+  | a::l => by simp only [flatMap_cons, map_append, map_flatMap _ _ l]
 
-theorem bind_map (f : α → β) (g : β → List γ) (l : List α) :
-    (map f l).bind g = l.bind (fun a => g (f a)) := by
-  induction l <;> simp [bind_cons, *]
+theorem flatMap_map (f : α → β) (g : β → List γ) (l : List α) :
+    (map f l).flatMap g = l.flatMap (fun a => g (f a)) := by
+  induction l <;> simp [flatMap_cons, *]
 
-theorem map_eq_bind {α β} (f : α → β) (l : List α) : map f l = l.bind fun x => [f x] := by
+theorem map_eq_flatMap {α β} (f : α → β) (l : List α) : map f l = l.flatMap fun x => [f x] := by
   simp only [← map_singleton]
-  rw [← bind_singleton' l, map_bind, bind_singleton']
+  rw [← flatMap_singleton' l, map_flatMap, flatMap_singleton']
 
-theorem filterMap_bind {β γ} (l : List α) (g : α → List β) (f : β → Option γ) :
-    (l.bind g).filterMap f = l.bind fun a => (g a).filterMap f := by
+theorem filterMap_flatMap {β γ} (l : List α) (g : α → List β) (f : β → Option γ) :
+    (l.flatMap g).filterMap f = l.flatMap fun a => (g a).filterMap f := by
   induction l <;> simp [*]
 
-theorem filter_bind (l : List α) (g : α → List β) (f : β → Bool) :
-    (l.bind g).filter f = l.bind fun a => (g a).filter f := by
+theorem filter_flatMap (l : List α) (g : α → List β) (f : β → Bool) :
+    (l.flatMap g).filter f = l.flatMap fun a => (g a).filter f := by
   induction l <;> simp [*]
 
-theorem bind_eq_foldl (f : α → List β) (l : List α) :
-    l.bind f = l.foldl (fun acc a => acc ++ f a) [] := by
-  suffices ∀ l', l' ++ l.bind f = l.foldl (fun acc a => acc ++ f a) l' by simpa using this []
+theorem flatMap_eq_foldl (f : α → List β) (l : List α) :
+    l.flatMap f = l.foldl (fun acc a => acc ++ f a) [] := by
+  suffices ∀ l', l' ++ l.flatMap f = l.foldl (fun acc a => acc ++ f a) l' by simpa using this []
   intro l'
   induction l generalizing l'
   · simp
-  · next ih => rw [bind_cons, ← append_assoc, ih, foldl_cons]
+  · next ih => rw [flatMap_cons, ← append_assoc, ih, foldl_cons]
 
 /-! ### replicate -/
 
@@ -2387,11 +2457,21 @@ theorem map_eq_replicate_iff {l : List α} {f : α → β} {b : β} :
 @[simp] theorem map_const (l : List α) (b : β) : map (Function.const α b) l = replicate l.length b :=
   map_eq_replicate_iff.mpr fun _ _ => rfl
 
+@[simp] theorem map_const_fun (x : β) : map (Function.const α x) = (replicate ·.length x) := by
+  funext l
+  simp
+
 /-- Variant of `map_const` using a lambda rather than `Function.const`. -/
 -- This can not be a `@[simp]` lemma because it would fire on every `List.map`.
 theorem map_const' (l : List α) (b : β) : map (fun _ => b) l = replicate l.length b :=
   map_const l b
 
+@[simp] theorem set_replicate_self : (replicate n a).set i a = replicate n a := by
+  apply ext_getElem
+  · simp
+  · intro i h₁ h₂
+    simp [getElem_set]
+
 @[simp] theorem append_replicate_replicate : replicate n a ++ replicate m a = replicate (n + m) a := by
   rw [eq_replicate_iff]
   constructor
@@ -2451,23 +2531,23 @@ theorem filterMap_replicate_of_some {f : α → Option β} (h : f a = some b) :
     (replicate n a).filterMap f = [] := by
   simp [filterMap_replicate, h]
 
-@[simp] theorem join_replicate_nil : (replicate n ([] : List α)).join = [] := by
+@[simp] theorem flatten_replicate_nil : (replicate n ([] : List α)).flatten = [] := by
   induction n <;> simp_all [replicate_succ]
 
-@[simp] theorem join_replicate_singleton : (replicate n [a]).join = replicate n a := by
+@[simp] theorem flatten_replicate_singleton : (replicate n [a]).flatten = replicate n a := by
   induction n <;> simp_all [replicate_succ]
 
-@[simp] theorem join_replicate_replicate : (replicate n (replicate m a)).join = replicate (n * m) a := by
+@[simp] theorem flatten_replicate_replicate : (replicate n (replicate m a)).flatten = replicate (n * m) a := by
   induction n with
   | zero => simp
   | succ n ih =>
-    simp only [replicate_succ, join_cons, ih, append_replicate_replicate, replicate_inj, or_true,
+    simp only [replicate_succ, flatten_cons, ih, append_replicate_replicate, replicate_inj, or_true,
       and_true, add_one_mul, Nat.add_comm]
 
-theorem bind_replicate {β} (f : α → List β) : (replicate n a).bind f = (replicate n (f a)).join := by
+theorem flatMap_replicate {β} (f : α → List β) : (replicate n a).flatMap f = (replicate n (f a)).flatten := by
   induction n with
   | zero => simp
-  | succ n ih => simp only [replicate_succ, bind_cons, ih, join_cons]
+  | succ n ih => simp only [replicate_succ, flatMap_cons, ih, flatten_cons]
 
 @[simp] theorem isEmpty_replicate : (replicate n a).isEmpty = decide (n = 0) := by
   cases n <;> simp [replicate_succ]
@@ -2642,20 +2722,20 @@ theorem reverse_eq_concat {xs ys : List α} {a : α} :
     xs.reverse = ys ++ [a] ↔ xs = a :: ys.reverse := by
   rw [reverse_eq_iff, reverse_concat]
 
-/-- Reversing a join is the same as reversing the order of parts and reversing all parts. -/
-theorem reverse_join (L : List (List α)) :
-    L.join.reverse = (L.map reverse).reverse.join := by
+/-- Reversing a flatten is the same as reversing the order of parts and reversing all parts. -/
+theorem reverse_flatten (L : List (List α)) :
+    L.flatten.reverse = (L.map reverse).reverse.flatten := by
   induction L <;> simp_all
 
-/-- Joining a reverse is the same as reversing all parts and reversing the joined result. -/
-theorem join_reverse (L : List (List α)) :
-    L.reverse.join = (L.map reverse).join.reverse := by
+/-- Flattening a reverse is the same as reversing all parts and reversing the flattened result. -/
+theorem flatten_reverse (L : List (List α)) :
+    L.reverse.flatten = (L.map reverse).flatten.reverse := by
   induction L <;> simp_all
 
-theorem reverse_bind {β} (l : List α) (f : α → List β) : (l.bind f).reverse = l.reverse.bind (reverse ∘ f) := by
+theorem reverse_flatMap {β} (l : List α) (f : α → List β) : (l.flatMap f).reverse = l.reverse.flatMap (reverse ∘ f) := by
   induction l <;> simp_all
 
-theorem bind_reverse {β} (l : List α) (f : α → List β) : (l.reverse.bind f) = (l.bind (reverse ∘ f)).reverse := by
+theorem flatMap_reverse {β} (l : List α) (f : α → List β) : (l.reverse.flatMap f) = (l.flatMap (reverse ∘ f)).reverse := by
   induction l <;> simp_all
 
 @[simp] theorem reverseAux_eq (as bs : List α) : reverseAux as bs = reverse as ++ bs :=
@@ -2672,10 +2752,16 @@ theorem bind_reverse {β} (l : List α) (f : α → List β) : (l.reverse.bind f
     l.reverse.foldr f b = l.foldl (fun x y => f y x) b :=
   (foldl_reverse ..).symm.trans <| by simp
 
+theorem foldl_eq_foldr_reverse (l : List α) (f : β → α → β) (b) :
+    l.foldl f b = l.reverse.foldr (fun x y => f y x) b := by simp
+
+theorem foldr_eq_foldl_reverse (l : List α) (f : α → β → β) (b) :
+    l.foldr f b = l.reverse.foldl (fun x y => f y x) b := by simp
+
 @[simp] theorem reverse_replicate (n) (a : α) : reverse (replicate n a) = replicate n a :=
   eq_replicate_iff.2
     ⟨by rw [length_reverse, length_replicate],
-     fun b h => eq_of_mem_replicate (mem_reverse.1 h)⟩
+     fun _ h => eq_of_mem_replicate (mem_reverse.1 h)⟩
 
 /-! #### Further results about `getLast` and `getLast?` -/
 
@@ -2763,15 +2849,15 @@ theorem getLast_filterMap_of_eq_some {f : α → Option β} {l : List α} {w : l
   rw [head_filterMap_of_eq_some (by simp_all)]
   simp_all
 
-theorem getLast?_bind {L : List α} {f : α → List β} :
-    (L.bind f).getLast? = L.reverse.findSome? fun a => (f a).getLast? := by
-  simp only [← head?_reverse, reverse_bind]
-  rw [head?_bind]
+theorem getLast?_flatMap {L : List α} {f : α → List β} :
+    (L.flatMap f).getLast? = L.reverse.findSome? fun a => (f a).getLast? := by
+  simp only [← head?_reverse, reverse_flatMap]
+  rw [head?_flatMap]
   rfl
 
-theorem getLast?_join {L : List (List α)} :
-    (join L).getLast? = L.reverse.findSome? fun l => l.getLast? := by
-  simp [← bind_id, getLast?_bind]
+theorem getLast?_flatten {L : List (List α)} :
+    (flatten L).getLast? = L.reverse.findSome? fun l => l.getLast? := by
+  simp [← flatMap_id, getLast?_flatMap]
 
 theorem getLast?_replicate (a : α) (n : Nat) : (replicate n a).getLast? = if n = 0 then none else some a := by
   simp only [← head?_reverse, reverse_replicate, head?_replicate]
@@ -2815,6 +2901,10 @@ theorem contains_iff_exists_mem_beq [BEq α] {l : List α} {a : α} :
     l.contains a ↔ ∃ a' ∈ l, a == a' := by
   induction l <;> simp_all
 
+theorem contains_iff_mem [BEq α] [LawfulBEq α] {l : List α} {a : α} :
+    l.contains a ↔ a ∈ l := by
+  simp
+
 /-! ## Sublists -/
 
 /-! ### partition
@@ -2880,7 +2970,7 @@ theorem head?_dropLast (xs : List α) : xs.dropLast.head? = if 1 < xs.length the
 
 theorem getLast_dropLast {xs : List α} (h) :
    xs.dropLast.getLast h =
-     xs[xs.length - 2]'(match xs, h with | (a :: b :: xs), _ => Nat.lt_trans (Nat.lt_add_one _) (Nat.lt_add_one _)) := by
+     xs[xs.length - 2]'(match xs, h with | (_ :: _ :: _), _ => Nat.lt_trans (Nat.lt_add_one _) (Nat.lt_add_one _)) := by
   rw [getLast_eq_getElem, getElem_dropLast]
   congr 1
   simp; rfl
@@ -2904,8 +2994,8 @@ theorem dropLast_cons_of_ne_nil {α : Type u} {x : α}
 
 theorem dropLast_concat_getLast : ∀ {l : List α} (h : l ≠ []), dropLast l ++ [getLast l h] = l
   | [], h => absurd rfl h
-  | [a], h => rfl
-  | a :: b :: l, h => by
+  | [_], _ => rfl
+  | _ :: b :: l, _ => by
     rw [dropLast_cons₂, cons_append, getLast_cons (cons_ne_nil _ _)]
     congr
     exact dropLast_concat_getLast (cons_ne_nil b l)
@@ -3270,18 +3360,22 @@ theorem all_eq_not_any_not (l : List α) (p : α → Bool) : l.all p = !l.any (!
   | nil => rfl
   | cons h t ih => simp_all [Bool.and_assoc]
 
-@[simp] theorem any_join {l : List (List α)} : l.join.any f = l.any (any · f) := by
+@[simp] theorem any_flatten {l : List (List α)} : l.flatten.any f = l.any (any · f) := by
   induction l <;> simp_all
 
-@[simp] theorem all_join {l : List (List α)} : l.join.all f = l.all (all · f) := by
+@[deprecated any_flatten (since := "2024-10-14")] abbrev any_join := @any_flatten
+
+@[simp] theorem all_flatten {l : List (List α)} : l.flatten.all f = l.all (all · f) := by
   induction l <;> simp_all
 
-@[simp] theorem any_bind {l : List α} {f : α → List β} :
-    (l.bind f).any p = l.any fun a => (f a).any p := by
+@[deprecated all_flatten (since := "2024-10-14")] abbrev all_join := @all_flatten
+
+@[simp] theorem any_flatMap {l : List α} {f : α → List β} :
+    (l.flatMap f).any p = l.any fun a => (f a).any p := by
   induction l <;> simp_all
 
-@[simp] theorem all_bind {l : List α} {f : α → List β} :
-    (l.bind f).all p = l.all fun a => (f a).all p := by
+@[simp] theorem all_flatMap {l : List α} {f : α → List β} :
+    (l.flatMap f).all p = l.all fun a => (f a).all p := by
   induction l <;> simp_all
 
 @[simp] theorem any_reverse {l : List α} : l.reverse.any f = l.any f := by
@@ -3296,7 +3390,7 @@ theorem all_eq_not_any_not (l : List α) (p : α → Bool) : l.all p = !l.any (!
 
 @[simp] theorem all_replicate {n : Nat} {a : α} :
     (replicate n a).all f = if n = 0 then true else f a := by
-  cases n <;> simp (config := {contextual := true}) [replicate_succ]
+  cases n <;> simp +contextual [replicate_succ]
 
 @[simp] theorem any_insert [BEq α] [LawfulBEq α] {l : List α} {a : α} :
     (l.insert a).any f = (f a || l.any f) := by
@@ -3306,4 +3400,72 @@ theorem all_eq_not_any_not (l : List α) (p : α → Bool) : l.all p = !l.any (!
     (l.insert a).all f = (f a && l.all f) := by
   simp [all_eq]
 
+/-! ### Deprecations -/
+
+
+@[deprecated flatten_nil (since := "2024-10-14")] abbrev join_nil := @flatten_nil
+@[deprecated flatten_cons (since := "2024-10-14")] abbrev join_cons := @flatten_cons
+@[deprecated length_flatten (since := "2024-10-14")] abbrev length_join := @length_flatten
+@[deprecated flatten_singleton (since := "2024-10-14")] abbrev join_singleton := @flatten_singleton
+@[deprecated mem_flatten (since := "2024-10-14")] abbrev mem_join := @mem_flatten
+@[deprecated flatten_eq_nil_iff (since := "2024-09-05")] abbrev join_eq_nil := @flatten_eq_nil_iff
+@[deprecated flatten_eq_nil_iff (since := "2024-10-14")] abbrev join_eq_nil_iff := @flatten_eq_nil_iff
+@[deprecated flatten_ne_nil_iff (since := "2024-09-05")] abbrev join_ne_nil := @flatten_ne_nil_iff
+@[deprecated flatten_ne_nil_iff (since := "2024-10-14")] abbrev join_ne_nil_iff := @flatten_ne_nil_iff
+@[deprecated exists_of_mem_flatten (since := "2024-10-14")] abbrev exists_of_mem_join := @exists_of_mem_flatten
+@[deprecated mem_flatten_of_mem (since := "2024-10-14")] abbrev mem_join_of_mem := @mem_flatten_of_mem
+@[deprecated forall_mem_flatten (since := "2024-10-14")] abbrev forall_mem_join := @forall_mem_flatten
+@[deprecated flatten_eq_flatMap (since := "2024-10-14")] abbrev join_eq_bind := @flatten_eq_flatMap
+@[deprecated head?_flatten (since := "2024-10-14")] abbrev head?_join := @head?_flatten
+@[deprecated foldl_flatten (since := "2024-10-14")] abbrev foldl_join := @foldl_flatten
+@[deprecated foldr_flatten (since := "2024-10-14")] abbrev foldr_join := @foldr_flatten
+@[deprecated map_flatten (since := "2024-10-14")] abbrev map_join := @map_flatten
+@[deprecated filterMap_flatten (since := "2024-10-14")] abbrev filterMap_join := @filterMap_flatten
+@[deprecated filter_flatten (since := "2024-10-14")] abbrev filter_join := @filter_flatten
+@[deprecated flatten_filter_not_isEmpty (since := "2024-10-14")] abbrev join_filter_not_isEmpty := @flatten_filter_not_isEmpty
+@[deprecated flatten_filter_ne_nil (since := "2024-10-14")] abbrev join_filter_ne_nil := @flatten_filter_ne_nil
+@[deprecated filter_flatten (since := "2024-08-26")]
+theorem join_map_filter (p : α → Bool) (l : List (List α)) :
+    (l.map (filter p)).flatten = (l.flatten).filter p := by
+  rw [filter_flatten]
+@[deprecated flatten_append (since := "2024-10-14")] abbrev join_append := @flatten_append
+@[deprecated flatten_concat (since := "2024-10-14")] abbrev join_concat := @flatten_concat
+@[deprecated flatten_flatten (since := "2024-10-14")] abbrev join_join := @flatten_flatten
+@[deprecated flatten_eq_cons_iff (since := "2024-09-05")] abbrev join_eq_cons_iff := @flatten_eq_cons_iff
+@[deprecated flatten_eq_cons_iff (since := "2024-09-05")] abbrev join_eq_cons := @flatten_eq_cons_iff
+@[deprecated flatten_eq_append_iff (since := "2024-09-05")] abbrev join_eq_append := @flatten_eq_append_iff
+@[deprecated flatten_eq_append_iff (since := "2024-10-14")] abbrev join_eq_append_iff := @flatten_eq_append_iff
+@[deprecated eq_iff_flatten_eq (since := "2024-10-14")] abbrev eq_iff_join_eq := @eq_iff_flatten_eq
+@[deprecated flatten_replicate_nil (since := "2024-10-14")] abbrev join_replicate_nil := @flatten_replicate_nil
+@[deprecated flatten_replicate_singleton (since := "2024-10-14")] abbrev join_replicate_singleton := @flatten_replicate_singleton
+@[deprecated flatten_replicate_replicate (since := "2024-10-14")] abbrev join_replicate_replicate := @flatten_replicate_replicate
+@[deprecated reverse_flatten (since := "2024-10-14")] abbrev reverse_join := @reverse_flatten
+@[deprecated flatten_reverse (since := "2024-10-14")] abbrev join_reverse := @flatten_reverse
+@[deprecated getLast?_flatten (since := "2024-10-14")] abbrev getLast?_join := @getLast?_flatten
+@[deprecated flatten_eq_flatMap (since := "2024-10-16")] abbrev flatten_eq_bind := @flatten_eq_flatMap
+@[deprecated flatMap_def (since := "2024-10-16")] abbrev bind_def := @flatMap_def
+@[deprecated flatMap_id (since := "2024-10-16")] abbrev bind_id := @flatMap_id
+@[deprecated mem_flatMap (since := "2024-10-16")] abbrev mem_bind := @mem_flatMap
+@[deprecated exists_of_mem_flatMap (since := "2024-10-16")] abbrev exists_of_mem_bind := @exists_of_mem_flatMap
+@[deprecated mem_flatMap_of_mem (since := "2024-10-16")] abbrev mem_bind_of_mem := @mem_flatMap_of_mem
+@[deprecated flatMap_eq_nil_iff (since := "2024-10-16")] abbrev bind_eq_nil_iff := @flatMap_eq_nil_iff
+@[deprecated forall_mem_flatMap (since := "2024-10-16")] abbrev forall_mem_bind := @forall_mem_flatMap
+@[deprecated flatMap_singleton (since := "2024-10-16")] abbrev bind_singleton := @flatMap_singleton
+@[deprecated flatMap_singleton' (since := "2024-10-16")] abbrev bind_singleton' := @flatMap_singleton'
+@[deprecated head?_flatMap (since := "2024-10-16")] abbrev head_bind := @head?_flatMap
+@[deprecated flatMap_append (since := "2024-10-16")] abbrev bind_append := @flatMap_append
+@[deprecated flatMap_assoc (since := "2024-10-16")] abbrev bind_assoc := @flatMap_assoc
+@[deprecated map_flatMap (since := "2024-10-16")] abbrev map_bind := @map_flatMap
+@[deprecated flatMap_map (since := "2024-10-16")] abbrev bind_map := @flatMap_map
+@[deprecated map_eq_flatMap (since := "2024-10-16")] abbrev map_eq_bind := @map_eq_flatMap
+@[deprecated filterMap_flatMap (since := "2024-10-16")] abbrev filterMap_bind := @filterMap_flatMap
+@[deprecated filter_flatMap (since := "2024-10-16")] abbrev filter_bind := @filter_flatMap
+@[deprecated flatMap_eq_foldl (since := "2024-10-16")] abbrev bind_eq_foldl := @flatMap_eq_foldl
+@[deprecated flatMap_replicate (since := "2024-10-16")] abbrev bind_replicate := @flatMap_replicate
+@[deprecated reverse_flatMap (since := "2024-10-16")] abbrev reverse_bind := @reverse_flatMap
+@[deprecated flatMap_reverse (since := "2024-10-16")] abbrev bind_reverse := @flatMap_reverse
+@[deprecated getLast?_flatMap (since := "2024-10-16")] abbrev getLast?_bind := @getLast?_flatMap
+@[deprecated any_flatMap (since := "2024-10-16")] abbrev any_bind := @any_flatMap
+@[deprecated all_flatMap (since := "2024-10-16")] abbrev all_bind := @all_flatMap
+
 end List

src/Init/Data/List/MapIdx.lean

@@ -0,0 +1,408 @@
+/-
+Copyright (c) 2024 Lean FRO. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Kim Morrison, Mario Carneiro
+-/
+
+prelude
+import Init.Data.Array.Lemmas
+import Init.Data.List.Nat.Range
+import Init.Data.List.OfFn
+import Init.Data.Fin.Lemmas
+import Init.Data.Option.Attach
+
+namespace List
+
+/-! ## Operations using indexes -/
+
+/-! ### mapIdx -/
+
+
+/--
+Given a list `as = [a₀, a₁, ...]` function `f : Fin as.length → α → β`, returns the list
+`[f 0 a₀, f 1 a₁, ...]`.
+-/
+@[inline] def mapFinIdx (as : List α) (f : Fin as.length → α → β) : List β := go as #[] (by simp) where
+  /-- Auxiliary for `mapFinIdx`:
+  `mapFinIdx.go [a₀, a₁, ...] acc = acc.toList ++ [f 0 a₀, f 1 a₁, ...]` -/
+  @[specialize] go : (bs : List α) → (acc : Array β) → bs.length + acc.size = as.length → List β
+  | [], acc, h => acc.toList
+  | a :: as, acc, h =>
+    go as (acc.push (f ⟨acc.size, by simp at h; omega⟩ a)) (by simp at h ⊢; omega)
+
+/--
+Given a function `f : Nat → α → β` and `as : List α`, `as = [a₀, a₁, ...]`, returns the list
+`[f 0 a₀, f 1 a₁, ...]`.
+-/
+@[inline] def mapIdx (f : Nat → α → β) (as : List α) : List β := go as #[] where
+  /-- Auxiliary for `mapIdx`:
+  `mapIdx.go [a₀, a₁, ...] acc = acc.toList ++ [f acc.size a₀, f (acc.size + 1) a₁, ...]` -/
+  @[specialize] go : List α → Array β → List β
+  | [], acc => acc.toList
+  | a :: as, acc => go as (acc.push (f acc.size a))
+
+/-! ### mapFinIdx -/
+
+@[simp]
+theorem mapFinIdx_nil {f : Fin 0 → α → β} : mapFinIdx [] f = [] :=
+  rfl
+
+@[simp] theorem length_mapFinIdx_go :
+    (mapFinIdx.go as f bs acc h).length = as.length := by
+  induction bs generalizing acc with
+  | nil => simpa using h
+  | cons _ _ ih => simp [mapFinIdx.go, ih]
+
+@[simp] theorem length_mapFinIdx {as : List α} {f : Fin as.length → α → β} :
+    (as.mapFinIdx f).length = as.length := by
+  simp [mapFinIdx, length_mapFinIdx_go]
+
+theorem getElem_mapFinIdx_go {as : List α} {f : Fin as.length → α → β} {i : Nat} {h} {w} :
+    (mapFinIdx.go as f bs acc h)[i] =
+      if w' : i < acc.size then acc[i] else f ⟨i, by simp at w; omega⟩ (bs[i - acc.size]'(by simp at w; omega)) := by
+  induction bs generalizing acc with
+  | nil =>
+    simp only [length_mapFinIdx_go, length_nil, Nat.zero_add] at w h
+    simp only [mapFinIdx.go, Array.getElem_toList]
+    rw [dif_pos]
+  | cons _ _ ih =>
+    simp [mapFinIdx.go]
+    rw [ih]
+    simp
+    split <;> rename_i h₁ <;> split <;> rename_i h₂
+    · rw [Array.getElem_push_lt]
+    · have h₃ : i = acc.size := by omega
+      subst h₃
+      simp
+    · omega
+    · have h₃ : i - acc.size = (i - (acc.size + 1)) + 1 := by omega
+      simp [h₃]
+
+@[simp] theorem getElem_mapFinIdx {as : List α} {f : Fin as.length → α → β} {i : Nat} {h} :
+    (as.mapFinIdx f)[i] = f ⟨i, by simp at h; omega⟩ (as[i]'(by simp at h; omega)) := by
+  simp [mapFinIdx, getElem_mapFinIdx_go]
+
+theorem mapFinIdx_eq_ofFn {as : List α} {f : Fin as.length → α → β} :
+    as.mapFinIdx f = List.ofFn fun i : Fin as.length => f i as[i] := by
+  apply ext_getElem <;> simp
+
+@[simp] theorem getElem?_mapFinIdx {l : List α} {f : Fin l.length → α → β} {i : Nat} :
+    (l.mapFinIdx f)[i]? = l[i]?.pbind fun x m => f ⟨i, by simp [getElem?_eq_some] at m; exact m.1⟩ x := by
+  simp only [getElem?_eq, length_mapFinIdx, getElem_mapFinIdx]
+  split <;> simp
+
+@[simp]
+theorem mapFinIdx_cons {l : List α} {a : α} {f : Fin (l.length + 1) → α → β} :
+    mapFinIdx (a :: l) f = f 0 a :: mapFinIdx l (fun i => f i.succ) := by
+  apply ext_getElem
+  · simp
+  · rintro (_|i) h₁ h₂ <;> simp
+
+theorem mapFinIdx_append {K L : List α} {f : Fin (K ++ L).length → α → β} :
+    (K ++ L).mapFinIdx f =
+      K.mapFinIdx (fun i => f (i.castLE (by simp))) ++ L.mapFinIdx (fun i => f ((i.natAdd K.length).cast (by simp))) := by
+  apply ext_getElem
+  · simp
+  · intro i h₁ h₂
+    rw [getElem_append]
+    simp only [getElem_mapFinIdx, length_mapFinIdx]
+    split <;> rename_i h
+    · rw [getElem_append_left]
+      congr
+    · simp only [Nat.not_lt] at h
+      rw [getElem_append_right h]
+      congr
+      simp
+      omega
+
+@[simp] theorem mapFinIdx_concat {l : List α} {e : α} {f : Fin (l ++ [e]).length → α → β}:
+    (l ++ [e]).mapFinIdx f = l.mapFinIdx (fun i => f (i.castLE (by simp))) ++ [f ⟨l.length, by simp⟩ e] := by
+  simp [mapFinIdx_append]
+  congr
+
+theorem mapFinIdx_singleton {a : α} {f : Fin 1 → α → β} :
+    [a].mapFinIdx f = [f ⟨0, by simp⟩ a] := by
+  simp
+
+theorem mapFinIdx_eq_enum_map {l : List α} {f : Fin l.length → α → β} :
+    l.mapFinIdx f = l.enum.attach.map
+      fun ⟨⟨i, x⟩, m⟩ => f ⟨i, by rw [mk_mem_enum_iff_getElem?, getElem?_eq_some] at m; exact m.1⟩ x := by
+  apply ext_getElem <;> simp
+
+@[simp]
+theorem mapFinIdx_eq_nil_iff {l : List α} {f : Fin l.length → α → β} :
+    l.mapFinIdx f = [] ↔ l = [] := by
+  rw [mapFinIdx_eq_enum_map, map_eq_nil_iff, attach_eq_nil_iff, enum_eq_nil_iff]
+
+theorem mapFinIdx_ne_nil_iff {l : List α} {f : Fin l.length → α → β} :
+    l.mapFinIdx f ≠ [] ↔ l ≠ [] := by
+  simp
+
+theorem exists_of_mem_mapFinIdx {b : β} {l : List α} {f : Fin l.length → α → β}
+    (h : b ∈ l.mapFinIdx f) : ∃ (i : Fin l.length), f i l[i] = b := by
+  rw [mapFinIdx_eq_enum_map] at h
+  replace h := exists_of_mem_map h
+  simp only [mem_attach, true_and, Subtype.exists, Prod.exists, mk_mem_enum_iff_getElem?] at h
+  obtain ⟨i, b, h, rfl⟩ := h
+  rw [getElem?_eq_some_iff] at h
+  obtain ⟨h', rfl⟩ := h
+  exact ⟨⟨i, h'⟩, rfl⟩
+
+@[simp] theorem mem_mapFinIdx {b : β} {l : List α} {f : Fin l.length → α → β} :
+    b ∈ l.mapFinIdx f ↔ ∃ (i : Fin l.length), f i l[i] = b := by
+  constructor
+  · intro h
+    exact exists_of_mem_mapFinIdx h
+  · rintro ⟨i, h, rfl⟩
+    rw [mem_iff_getElem]
+    exact ⟨i, by simp⟩
+
+theorem mapFinIdx_eq_cons_iff {l : List α} {b : β} {f : Fin l.length → α → β} :
+    l.mapFinIdx f = b :: l₂ ↔
+      ∃ (a : α) (l₁ : List α) (h : l = a :: l₁),
+        f ⟨0, by simp [h]⟩ a = b ∧ l₁.mapFinIdx (fun i => f (i.succ.cast (by simp [h]))) = l₂ := by
+  cases l with
+  | nil => simp
+  | cons x l' =>
+    simp only [mapFinIdx_cons, cons.injEq, length_cons, Fin.zero_eta, Fin.cast_succ_eq,
+      exists_and_left]
+    constructor
+    · rintro ⟨rfl, rfl⟩
+      refine ⟨x, rfl, l', by simp⟩
+    · rintro ⟨a, ⟨rfl, h⟩, ⟨_, ⟨rfl, rfl⟩, h⟩⟩
+      exact ⟨rfl, h⟩
+
+theorem mapFinIdx_eq_cons_iff' {l : List α} {b : β} {f : Fin l.length → α → β} :
+    l.mapFinIdx f = b :: l₂ ↔
+      l.head?.pbind (fun x m => (f ⟨0, by cases l <;> simp_all⟩ x)) = some b ∧
+        l.tail?.attach.map (fun ⟨t, m⟩ => t.mapFinIdx fun i => f (i.succ.cast (by cases l <;> simp_all))) = some l₂ := by
+  cases l <;> simp
+
+theorem mapFinIdx_eq_iff {l : List α} {f : Fin l.length → α → β} :
+    l.mapFinIdx f = l' ↔ ∃ h : l'.length = l.length, ∀ (i : Nat) (h : i < l.length), l'[i] = f ⟨i, h⟩ l[i] := by
+  constructor
+  · rintro rfl
+    simp
+  · rintro ⟨h, w⟩
+    apply ext_getElem <;> simp_all
+
+theorem mapFinIdx_eq_mapFinIdx_iff {l : List α} {f g : Fin l.length → α → β} :
+    l.mapFinIdx f = l.mapFinIdx g ↔ ∀ (i : Fin l.length), f i l[i] = g i l[i] := by
+  rw [eq_comm, mapFinIdx_eq_iff]
+  simp [Fin.forall_iff]
+
+@[simp] theorem mapFinIdx_mapFinIdx {l : List α} {f : Fin l.length → α → β} {g : Fin _ → β → γ} :
+    (l.mapFinIdx f).mapFinIdx g = l.mapFinIdx (fun i => g (i.cast (by simp)) ∘ f i) := by
+  simp [mapFinIdx_eq_iff]
+
+theorem mapFinIdx_eq_replicate_iff {l : List α} {f : Fin l.length → α → β} {b : β} :
+    l.mapFinIdx f = replicate l.length b ↔ ∀ (i : Fin l.length), f i l[i] = b := by
+  simp [eq_replicate_iff, length_mapFinIdx, mem_mapFinIdx, forall_exists_index, true_and]
+
+@[simp] theorem mapFinIdx_reverse {l : List α} {f : Fin l.reverse.length → α → β} :
+    l.reverse.mapFinIdx f = (l.mapFinIdx (fun i => f ⟨l.length - 1 - i, by simp; omega⟩)).reverse := by
+  simp [mapFinIdx_eq_iff]
+  intro i h
+  congr
+  omega
+
+/-! ### mapIdx -/
+
+@[simp]
+theorem mapIdx_nil {f : Nat → α → β} : mapIdx f [] = [] :=
+  rfl
+
+theorem mapIdx_go_length {arr : Array β} :
+    length (mapIdx.go f l arr) = length l + arr.size := by
+  induction l generalizing arr with
+  | nil => simp only [mapIdx.go, length_nil, Nat.zero_add]
+  | cons _ _ ih =>
+    simp only [mapIdx.go, ih, Array.size_push, Nat.add_succ, length_cons, Nat.add_comm]
+
+theorem length_mapIdx_go : ∀ {l : List α} {arr : Array β},
+    (mapIdx.go f l arr).length = l.length + arr.size
+  | [], _ => by simp [mapIdx.go]
+  | a :: l, _ => by
+    simp only [mapIdx.go, length_cons]
+    rw [length_mapIdx_go]
+    simp
+    omega
+
+@[simp] theorem length_mapIdx {l : List α} : (l.mapIdx f).length = l.length := by
+  simp [mapIdx, length_mapIdx_go]
+
+theorem getElem?_mapIdx_go : ∀ {l : List α} {arr : Array β} {i : Nat},
+    (mapIdx.go f l arr)[i]? =
+      if h : i < arr.size then some arr[i] else Option.map (f i) l[i - arr.size]?
+  | [], arr, i => by
+    simp only [mapIdx.go, Array.toListImpl_eq, getElem?_eq, Array.length_toList,
+      Array.getElem_eq_getElem_toList, length_nil, Nat.not_lt_zero, ↓reduceDIte, Option.map_none']
+  | a :: l, arr, i => by
+    rw [mapIdx.go, getElem?_mapIdx_go]
+    simp only [Array.size_push]
+    split <;> split
+    · simp only [Option.some.injEq]
+      rw [Array.getElem_eq_getElem_toList]
+      simp only [Array.push_toList]
+      rw [getElem_append_left, Array.getElem_eq_getElem_toList]
+    · have : i = arr.size := by omega
+      simp_all
+    · omega
+    · have : i - arr.size = i - (arr.size + 1) + 1 := by omega
+      simp_all
+
+@[simp] theorem getElem?_mapIdx {l : List α} {i : Nat} :
+    (l.mapIdx f)[i]? = Option.map (f i) l[i]? := by
+  simp [mapIdx, getElem?_mapIdx_go]
+
+@[simp] theorem getElem_mapIdx {l : List α} {f : Nat → α → β} {i : Nat} {h : i < (l.mapIdx f).length} :
+    (l.mapIdx f)[i] = f i (l[i]'(by simpa using h)) := by
+  apply Option.some_inj.mp
+  rw [← getElem?_eq_getElem, getElem?_mapIdx, getElem?_eq_getElem (by simpa using h)]
+  simp
+
+@[simp] theorem mapFinIdx_eq_mapIdx {l : List α} {f : Fin l.length → α → β} {g : Nat → α → β}
+    (h : ∀ (i : Fin l.length), f i l[i] = g i l[i]) :
+    l.mapFinIdx f = l.mapIdx g := by
+  simp_all [mapFinIdx_eq_iff]
+
+theorem mapIdx_eq_mapFinIdx {l : List α} {f : Nat → α → β} :
+    l.mapIdx f = l.mapFinIdx (fun i => f i) := by
+  simp [mapFinIdx_eq_mapIdx]
+
+theorem mapIdx_eq_enum_map {l : List α} :
+    l.mapIdx f = l.enum.map (Function.uncurry f) := by
+  ext1 i
+  simp only [getElem?_mapIdx, Option.map, getElem?_map, getElem?_enum]
+  split <;> simp
+
+@[simp]
+theorem mapIdx_cons {l : List α} {a : α} :
+    mapIdx f (a :: l) = f 0 a :: mapIdx (fun i => f (i + 1)) l := by
+  simp [mapIdx_eq_enum_map, enum_eq_zip_range, map_uncurry_zip_eq_zipWith,
+    range_succ_eq_map, zipWith_map_left]
+
+theorem mapIdx_append {K L : List α} :
+    (K ++ L).mapIdx f = K.mapIdx f ++ L.mapIdx fun i => f (i + K.length) := by
+  induction K generalizing f with
+  | nil => rfl
+  | cons _ _ ih => simp [ih (f := fun i => f (i + 1)), Nat.add_assoc]
+
+@[simp] theorem mapIdx_concat {l : List α} {e : α} :
+    mapIdx f (l ++ [e]) = mapIdx f l ++ [f l.length e] := by
+  simp [mapIdx_append]
+
+theorem mapIdx_singleton {a : α} : mapIdx f [a] = [f 0 a] := by
+  simp
+
+@[simp]
+theorem mapIdx_eq_nil_iff {l : List α} : List.mapIdx f l = [] ↔ l = [] := by
+  rw [List.mapIdx_eq_enum_map, List.map_eq_nil_iff, List.enum_eq_nil_iff]
+
+theorem mapIdx_ne_nil_iff {l : List α} :
+    List.mapIdx f l ≠ [] ↔ l ≠ [] := by
+  simp
+
+theorem exists_of_mem_mapIdx {b : β} {l : List α}
+    (h : b ∈ mapIdx f l) : ∃ (i : Nat) (h : i < l.length), f i l[i] = b := by
+  rw [mapIdx_eq_mapFinIdx] at h
+  simpa [Fin.exists_iff] using exists_of_mem_mapFinIdx h
+
+@[simp] theorem mem_mapIdx {b : β} {l : List α} :
+    b ∈ mapIdx f l ↔ ∃ (i : Nat) (h : i < l.length), f i l[i] = b := by
+  constructor
+  · intro h
+    exact exists_of_mem_mapIdx h
+  · rintro ⟨i, h, rfl⟩
+    rw [mem_iff_getElem]
+    exact ⟨i, by simpa using h, by simp⟩
+
+theorem mapIdx_eq_cons_iff {l : List α} {b : β} :
+    mapIdx f l = b :: l₂ ↔
+      ∃ (a : α) (l₁ : List α), l = a :: l₁ ∧ f 0 a = b ∧ mapIdx (fun i => f (i + 1)) l₁ = l₂ := by
+  cases l <;> simp [and_assoc]
+
+theorem mapIdx_eq_cons_iff' {l : List α} {b : β} :
+    mapIdx f l = b :: l₂ ↔
+      l.head?.map (f 0) = some b ∧ l.tail?.map (mapIdx fun i => f (i + 1)) = some l₂ := by
+  cases l <;> simp
+
+theorem mapIdx_eq_iff {l : List α} : mapIdx f l = l' ↔ ∀ i : Nat, l'[i]? = l[i]?.map (f i) := by
+  constructor
+  · intro w i
+    simpa using congrArg (fun l => l[i]?) w.symm
+  · intro w
+    ext1 i
+    simp [w]
+
+theorem mapIdx_eq_mapIdx_iff {l : List α} :
+    mapIdx f l = mapIdx g l ↔ ∀ i : Nat, (h : i < l.length) → f i l[i] = g i l[i] := by
+  constructor
+  · intro w i h
+    simpa [h] using congrArg (fun l => l[i]?) w
+  · intro w
+    apply ext_getElem
+    · simp
+    · intro i h₁ h₂
+      simp [w]
+
+@[simp] theorem mapIdx_set {l : List α} {i : Nat} {a : α} :
+    (l.set i a).mapIdx f = (l.mapIdx f).set i (f i a) := by
+  simp only [mapIdx_eq_iff, getElem?_set, length_mapIdx, getElem?_mapIdx]
+  intro i
+  split
+  · split <;> simp_all
+  · rfl
+
+@[simp] theorem head_mapIdx {l : List α} {f : Nat → α → β} {w : mapIdx f l ≠ []} :
+    (mapIdx f l).head w = f 0 (l.head (by simpa using w)) := by
+  cases l with
+  | nil => simp at w
+  | cons _ _ => simp
+
+@[simp] theorem head?_mapIdx {l : List α} {f : Nat → α → β} : (mapIdx f l).head? = l.head?.map (f 0) := by
+  cases l <;> simp
+
+@[simp] theorem getLast_mapIdx {l : List α} {f : Nat → α → β} {h} :
+    (mapIdx f l).getLast h = f (l.length - 1) (l.getLast (by simpa using h)) := by
+  cases l with
+  | nil => simp at h
+  | cons _ _ =>
+    simp only [← getElem_cons_length _ _ _ rfl]
+    simp only [mapIdx_cons]
+    simp only [← getElem_cons_length _ _ _ rfl]
+    simp only [← mapIdx_cons, getElem_mapIdx]
+    simp
+
+@[simp] theorem getLast?_mapIdx {l : List α} {f : Nat → α → β} :
+    (mapIdx f l).getLast? = (getLast? l).map (f (l.length - 1)) := by
+  cases l
+  · simp
+  · rw [getLast?_eq_getLast, getLast?_eq_getLast, getLast_mapIdx] <;> simp
+
+@[simp] theorem mapIdx_mapIdx {l : List α} {f : Nat → α → β} {g : Nat → β → γ} :
+    (l.mapIdx f).mapIdx g = l.mapIdx (fun i => g i ∘ f i) := by
+  simp [mapIdx_eq_iff]
+
+theorem mapIdx_eq_replicate_iff {l : List α} {f : Nat → α → β} {b : β} :
+    mapIdx f l = replicate l.length b ↔ ∀ (i : Nat) (h : i < l.length), f i l[i] = b := by
+  simp only [eq_replicate_iff, length_mapIdx, mem_mapIdx, forall_exists_index, true_and]
+  constructor
+  · intro w i h
+    apply w _ _ _ rfl
+  · rintro w _ i h rfl
+    exact w i h
+
+@[simp] theorem mapIdx_reverse {l : List α} {f : Nat → α → β} :
+    l.reverse.mapIdx f = (mapIdx (fun i => f (l.length - 1 - i)) l).reverse := by
+  simp [mapIdx_eq_iff]
+  intro i
+  by_cases h : i < l.length
+  · simp [getElem?_reverse, h]
+    congr
+    omega
+  · simp at h
+    rw [getElem?_eq_none (by simp [h]), getElem?_eq_none (by simp [h])]
+    simp
+
+end List

src/Init/Data/List/MinMax.lean

@@ -7,7 +7,7 @@ prelude
 import Init.Data.List.Lemmas
 
 /-!
-# Lemmas about `List.minimum?` and `List.maximum?.
+# Lemmas about `List.min?` and `List.max?.
 -/
 
 namespace List
@@ -16,24 +16,32 @@ open Nat
 
 /-! ## Minima and maxima -/
 
-/-! ### minimum? -/
+/-! ### min? -/
 
-@[simp] theorem minimum?_nil [Min α] : ([] : List α).minimum? = none := rfl
+@[simp] theorem min?_nil [Min α] : ([] : List α).min? = none := rfl
 
--- We don't put `@[simp]` on `minimum?_cons`,
+-- We don't put `@[simp]` on `min?_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
+theorem min?_cons' [Min α] {xs : List α} : (x :: xs).min? = 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?]
+@[simp] theorem min?_cons [Min α] [Std.Associative (min : α → α → α)] {xs : List α} :
+    (x :: xs).min? = some (xs.min?.elim x (min x)) := by
+  cases xs <;> simp [min?_cons', foldl_assoc]
 
-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
+@[simp] theorem min?_eq_none_iff {xs : List α} [Min α] : xs.min? = none ↔ xs = [] := by
+  cases xs <;> simp [min?]
+
+theorem isSome_min?_of_mem {l : List α} [Min α] {a : α} (h : a ∈ l) :
+    l.min?.isSome := by
+  cases l <;> simp_all [List.min?_cons']
+
+theorem min?_mem [Min α] (min_eq_or : ∀ a b : α, min a b = a ∨ min a b = b) :
+    {xs : List α} → xs.min? = some a → a ∈ xs := by
   intro xs
   match xs with
   | nil => simp
   | x :: xs =>
-    simp only [minimum?_cons, Option.some.injEq, List.mem_cons]
+    simp only [min?_cons', Option.some.injEq, List.mem_cons]
     intro eq
     induction xs generalizing x with
     | nil =>
@@ -49,12 +57,12 @@ theorem minimum?_mem [Min α] (min_eq_or : ∀ a b : α, min a b = a ∨ min a b
 
 -- See also `Init.Data.List.Nat.Basic` for specialisations of the next two results to `Nat`.
 
-theorem le_minimum?_iff [Min α] [LE α]
+theorem le_min?_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
+    {xs : List α} → xs.min? = some a → ∀ {x}, x ≤ a ↔ ∀ b, b ∈ xs → x ≤ b
   | nil => by simp
   | cons x xs => by
-    rw [minimum?]
+    rw [min?]
     intro eq y
     simp only [Option.some.injEq] at eq
     induction xs generalizing x with
@@ -67,46 +75,58 @@ theorem le_minimum?_iff [Min α] [LE α]
 
 -- 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) ≤ ·)]
+theorem min?_eq_some_iff [Min α] [LE α] [anti : Std.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 _)⟩, ?_⟩
+    xs.min? = some a ↔ a ∈ xs ∧ ∀ b, b ∈ xs → a ≤ b := by
+  refine ⟨fun h => ⟨min?_mem min_eq_or h, (le_min?_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))
+      ((le_min?_iff le_min_iff (xs := x::xs) rfl).1 (le_refl _) _ h₁)
+      (h₂ _ (min?_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
+theorem min?_replicate [Min α] {n : Nat} {a : α} (w : min a a = a) :
+    (replicate n a).min? = 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]
+  | succ n ih => cases n <;> simp_all [replicate_succ, min?_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]
+@[simp] theorem min?_replicate_of_pos [Min α] {n : Nat} {a : α} (w : min a a = a) (h : 0 < n) :
+    (replicate n a).min? = some a := by
+  simp [min?_replicate, Nat.ne_of_gt h, w]
 
-/-! ### maximum? -/
+theorem foldl_min [Min α] [Std.IdempotentOp (min : α → α → α)] [Std.Associative (min : α → α → α)]
+    {l : List α} {a : α} : l.foldl (init := a) min = min a (l.min?.getD a) := by
+  cases l <;> simp [min?, foldl_assoc, Std.IdempotentOp.idempotent]
 
-@[simp] theorem maximum?_nil [Max α] : ([] : List α).maximum? = none := rfl
+/-! ### max? -/
 
--- We don't put `@[simp]` on `maximum?_cons`,
+@[simp] theorem max?_nil [Max α] : ([] : List α).max? = none := rfl
+
+-- We don't put `@[simp]` on `max?_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
+theorem max?_cons' [Max α] {xs : List α} : (x :: xs).max? = 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?]
+@[simp] theorem max?_cons [Max α] [Std.Associative (max : α → α → α)] {xs : List α} :
+    (x :: xs).max? = some (xs.max?.elim x (max x)) := by
+  cases xs <;> simp [max?_cons', foldl_assoc]
 
-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
+@[simp] theorem max?_eq_none_iff {xs : List α} [Max α] : xs.max? = none ↔ xs = [] := by
+  cases xs <;> simp [max?]
+
+theorem isSome_max?_of_mem {l : List α} [Max α] {a : α} (h : a ∈ l) :
+    l.max?.isSome := by
+  cases l <;> simp_all [List.max?_cons']
+
+theorem max?_mem [Max α] (min_eq_or : ∀ a b : α, max a b = a ∨ max a b = b) :
+    {xs : List α} → xs.max? = some a → a ∈ xs
   | nil => by simp
   | cons x xs => by
-    rw [maximum?]; rintro ⟨⟩
+    rw [max?]; rintro ⟨⟩
     induction xs generalizing x with simp at *
     | cons y xs ih =>
       rcases ih (max x y) with h | h <;> simp [h]
@@ -114,40 +134,61 @@ theorem maximum?_mem [Max α] (min_eq_or : ∀ a b : α, max a b = a ∨ max a b
 
 -- See also `Init.Data.List.Nat.Basic` for specialisations of the next two results to `Nat`.
 
-theorem maximum?_le_iff [Max α] [LE α]
+theorem max?_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
+    {xs : List α} → xs.max? = some a → ∀ {x}, a ≤ x ↔ ∀ b ∈ xs, b ≤ x
   | nil => by simp
   | cons x xs => by
-    rw [maximum?]; rintro ⟨⟩ y
+    rw [max?]; 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) ≤ ·)]
+theorem max?_eq_some_iff [Max α] [LE α] [anti : Std.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 _)⟩, ?_⟩
+    xs.max? = some a ↔ a ∈ xs ∧ ∀ b ∈ xs, b ≤ a := by
+  refine ⟨fun h => ⟨max?_mem max_eq_or h, (max?_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)
+      (h₂ _ (max?_mem max_eq_or (xs := x::xs) rfl))
+      ((max?_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
+theorem max?_replicate [Max α] {n : Nat} {a : α} (w : max a a = a) :
+    (replicate n a).max? = 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]
+  | succ n ih => cases n <;> simp_all [replicate_succ, max?_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]
+@[simp] theorem max?_replicate_of_pos [Max α] {n : Nat} {a : α} (w : max a a = a) (h : 0 < n) :
+    (replicate n a).max? = some a := by
+  simp [max?_replicate, Nat.ne_of_gt h, w]
+
+theorem foldl_max [Max α] [Std.IdempotentOp (max : α → α → α)] [Std.Associative (max : α → α → α)]
+    {l : List α} {a : α} : l.foldl (init := a) max = max a (l.max?.getD a) := by
+  cases l <;> simp [max?, foldl_assoc, Std.IdempotentOp.idempotent]
+
+@[deprecated min?_nil (since := "2024-09-29")] abbrev minimum?_nil := @min?_nil
+@[deprecated min?_cons (since := "2024-09-29")] abbrev minimum?_cons := @min?_cons
+@[deprecated min?_eq_none_iff (since := "2024-09-29")] abbrev mininmum?_eq_none_iff := @min?_eq_none_iff
+@[deprecated min?_mem (since := "2024-09-29")] abbrev minimum?_mem := @min?_mem
+@[deprecated le_min?_iff (since := "2024-09-29")] abbrev le_minimum?_iff := @le_min?_iff
+@[deprecated min?_eq_some_iff (since := "2024-09-29")] abbrev minimum?_eq_some_iff := @min?_eq_some_iff
+@[deprecated min?_replicate (since := "2024-09-29")] abbrev minimum?_replicate := @min?_replicate
+@[deprecated min?_replicate_of_pos (since := "2024-09-29")] abbrev minimum?_replicate_of_pos := @min?_replicate_of_pos
+@[deprecated max?_nil (since := "2024-09-29")] abbrev maximum?_nil := @max?_nil
+@[deprecated max?_cons (since := "2024-09-29")] abbrev maximum?_cons := @max?_cons
+@[deprecated max?_eq_none_iff (since := "2024-09-29")] abbrev maximum?_eq_none_iff := @max?_eq_none_iff
+@[deprecated max?_mem (since := "2024-09-29")] abbrev maximum?_mem := @max?_mem
+@[deprecated max?_le_iff (since := "2024-09-29")] abbrev maximum?_le_iff := @max?_le_iff
+@[deprecated max?_eq_some_iff (since := "2024-09-29")] abbrev maximum?_eq_some_iff := @max?_eq_some_iff
+@[deprecated max?_replicate (since := "2024-09-29")] abbrev maximum?_replicate := @max?_replicate
+@[deprecated max?_replicate_of_pos (since := "2024-09-29")] abbrev maximum?_replicate_of_pos := @max?_replicate_of_pos
 
 end List

src/Init/Data/List/Monadic.lean

@@ -5,6 +5,7 @@ Authors: Parikshit Khanna, Jeremy Avigad, Leonardo de Moura, Floris van Doorn, M
 -/
 prelude
 import Init.Data.List.TakeDrop
+import Init.Data.List.Attach
 
 /-!
 # Lemmas about `List.mapM` and `List.forM`.
@@ -48,9 +49,79 @@ theorem mapM'_eq_mapM [Monad m] [LawfulMonad m] (f : α → m β) (l : List α)
 @[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_id {l : List α} {f : α → Id β} : l.mapM f = l.map f := by
+  induction l <;> simp_all
+
 @[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 [*]
 
+/-- Auxiliary lemma for `mapM_eq_reverse_foldlM_cons`. -/
+theorem foldlM_cons_eq_append [Monad m] [LawfulMonad m] (f : α → m β) (as : List α) (b : β) (bs : List β) :
+    (as.foldlM (init := b :: bs) fun acc a => return ((← f a) :: acc)) =
+      (· ++ b :: bs) <$> as.foldlM (init := []) fun acc a => return ((← f a) :: acc) := by
+  induction as generalizing b bs with
+  | nil => simp
+  | cons a as ih =>
+    simp only [bind_pure_comp] at ih
+    simp [ih, _root_.map_bind, Functor.map_map, Function.comp_def]
+
+theorem mapM_eq_reverse_foldlM_cons [Monad m] [LawfulMonad m] (f : α → m β) (l : List α) :
+    mapM f l = reverse <$> (l.foldlM (fun acc a => return ((← f a) :: acc)) []) := by
+  rw [← mapM'_eq_mapM]
+  induction l with
+  | nil => simp
+  | cons a as ih =>
+    simp only [mapM'_cons, ih, bind_map_left, foldlM_cons, LawfulMonad.bind_assoc, pure_bind,
+      foldlM_cons_eq_append, _root_.map_bind, Functor.map_map, Function.comp_def, reverse_append,
+      reverse_cons, reverse_nil, nil_append, singleton_append]
+    simp [bind_pure_comp]
+
+/-! ### foldlM and foldrM -/
+
+theorem foldlM_map [Monad m] (f : β₁ → β₂) (g : α → β₂ → m α) (l : List β₁) (init : α) :
+    (l.map f).foldlM g init = l.foldlM (fun x y => g x (f y)) init := by
+  induction l generalizing g init <;> simp [*]
+
+theorem foldrM_map [Monad m] [LawfulMonad m] (f : β₁ → β₂) (g : β₂ → α → m α) (l : List β₁)
+    (init : α) : (l.map f).foldrM g init = l.foldrM (fun x y => g (f x) y) init := by
+  induction l generalizing g init <;> simp [*]
+
+theorem foldlM_filterMap [Monad m] [LawfulMonad m] (f : α → Option β) (g : γ → β → m γ) (l : List α) (init : γ) :
+    (l.filterMap f).foldlM g init =
+      l.foldlM (fun x y => match f y with | some b => g x b | none => pure x) init := by
+  induction l generalizing init with
+  | nil => rfl
+  | cons a l ih =>
+    simp only [filterMap_cons, foldlM_cons]
+    cases f a <;> simp [ih]
+
+theorem foldrM_filterMap [Monad m] [LawfulMonad m] (f : α → Option β) (g : β → γ → m γ) (l : List α) (init : γ) :
+    (l.filterMap f).foldrM g init =
+      l.foldrM (fun x y => match f x with | some b => g b y | none => pure y) init := by
+  induction l generalizing init with
+  | nil => rfl
+  | cons a l ih =>
+    simp only [filterMap_cons, foldrM_cons]
+    cases f a <;> simp [ih]
+
+theorem foldlM_filter [Monad m] [LawfulMonad m] (p : α → Bool) (g : β → α → m β) (l : List α) (init : β) :
+    (l.filter p).foldlM g init =
+      l.foldlM (fun x y => if p y then g x y else pure x) init := by
+  induction l generalizing init with
+  | nil => rfl
+  | cons a l ih =>
+    simp only [filter_cons, foldlM_cons]
+    split <;> simp [ih]
+
+theorem foldrM_filter [Monad m] [LawfulMonad m] (p : α → Bool) (g : α → β → m β) (l : List α) (init : β) :
+    (l.filter p).foldrM g init =
+      l.foldrM (fun x y => if p x then g x y else pure y) init := by
+  induction l generalizing init with
+  | nil => rfl
+  | cons a l ih =>
+    simp only [filter_cons, foldrM_cons]
+    split <;> simp [ih]
+
 /-! ### forM -/
 
 -- We use `List.forM` as the simp normal form, rather that `ForM.forM`.
@@ -66,4 +137,186 @@ theorem mapM'_eq_mapM [Monad m] [LawfulMonad m] (f : α → m β) (l : List α)
     (l₁ ++ l₂).forM f = (do l₁.forM f; l₂.forM f) := by
   induction l₁ <;> simp [*]
 
+/-! ### forIn' -/
+
+theorem forIn'_loop_congr [Monad m] {as bs : List α}
+    {f : (a' : α) → a' ∈ as → β → m (ForInStep β)}
+    {g : (a' : α) → a' ∈ bs → β → m (ForInStep β)}
+    {b : β} (ha : ∃ ys, ys ++ xs = as) (hb : ∃ ys, ys ++ xs = bs)
+    (h : ∀ a m m' b, f a m b = g a m' b) : forIn'.loop as f xs b ha = forIn'.loop bs g xs b hb  := by
+  induction xs generalizing b with
+  | nil => simp [forIn'.loop]
+  | cons a xs ih =>
+    simp only [forIn'.loop] at *
+    congr 1
+    · rw [h]
+    · funext s
+      obtain b | b := s
+      · rfl
+      · simp
+        rw [ih]
+
+@[simp] theorem forIn'_cons [Monad m] {a : α} {as : List α}
+    (f : (a' : α) → a' ∈ a :: as → β → m (ForInStep β)) (b : β) :
+    forIn' (a::as) b f = f a (mem_cons_self a as) b >>=
+      fun | ForInStep.done b => pure b | ForInStep.yield b => forIn' as b fun a' m b => f a' (mem_cons_of_mem a m) b := by
+  simp only [forIn', List.forIn', forIn'.loop]
+  congr 1
+  funext s
+  obtain b | b := s
+  · rfl
+  · apply forIn'_loop_congr
+    intros
+    rfl
+
+@[simp] theorem forIn_cons [Monad m] (f : α → β → m (ForInStep β)) (a : α) (as : List α) (b : β) :
+    forIn (a::as) b f = f a b >>= fun | ForInStep.done b => pure b | ForInStep.yield b => forIn as b f := by
+  have := forIn'_cons (a := a) (as := as) (fun a' _ b => f a' b) b
+  simpa only [forIn'_eq_forIn]
+
+@[congr] theorem forIn'_congr [Monad m] {as bs : List α} (w : as = bs)
+    {b b' : β} (hb : b = b')
+    {f : (a' : α) → a' ∈ as → β → m (ForInStep β)}
+    {g : (a' : α) → a' ∈ bs → β → m (ForInStep β)}
+    (h : ∀ a m b, f a (by simpa [w] using m) b = g a m b) :
+    forIn' as b f = forIn' bs b' g := by
+  induction bs generalizing as b b' with
+  | nil =>
+    subst w
+    simp [hb, forIn'_nil]
+  | cons b bs ih =>
+    cases as with
+    | nil => simp at w
+    | cons a as =>
+      simp only [cons.injEq] at w
+      obtain ⟨rfl, rfl⟩ := w
+      simp only [forIn'_cons]
+      congr 1
+      · simp [h, hb]
+      · funext s
+        obtain b | b := s
+        · rfl
+        · simp
+          rw [ih rfl rfl]
+          intro a m b
+          exact h a (mem_cons_of_mem _ m) b
+
+/--
+We can express a for loop over a list as a fold,
+in which whenever we reach `.done b` we keep that value through the rest of the fold.
+-/
+theorem forIn'_eq_foldlM [Monad m] [LawfulMonad m]
+    (l : List α) (f : (a : α) → a ∈ l → β → m (ForInStep β)) (init : β) :
+    forIn' l init f = ForInStep.value <$>
+      l.attach.foldlM (fun b ⟨a, m⟩ => match b with
+        | .yield b => f a m b
+        | .done b => pure (.done b)) (ForInStep.yield init) := by
+  induction l generalizing init with
+  | nil => simp
+  | cons a as ih =>
+    simp only [forIn'_cons, attach_cons, foldlM_cons, _root_.map_bind]
+    congr 1
+    funext x
+    match x with
+    | .done b =>
+      clear ih
+      dsimp
+      induction as with
+      | nil => simp
+      | cons a as ih =>
+        simp only [attach_cons, map_cons, map_map, Function.comp_def, foldlM_cons, pure_bind]
+        specialize ih (fun a m b => f a (by
+          simp only [mem_cons] at m
+          rcases m with rfl|m
+          · apply mem_cons_self
+          · exact mem_cons_of_mem _ (mem_cons_of_mem _ m)) b)
+        simp [ih, List.foldlM_map]
+    | .yield b =>
+      simp [ih, List.foldlM_map]
+
+/-- We can express a for loop over a list which always yields as a fold. -/
+@[simp] theorem forIn'_yield_eq_foldlM [Monad m] [LawfulMonad m]
+    (l : List α) (f : (a : α) → a ∈ l → β → m γ) (g : (a : α) → a ∈ l → β → γ → β) (init : β) :
+    forIn' l init (fun a m b => (fun c => .yield (g a m b c)) <$> f a m b) =
+      l.attach.foldlM (fun b ⟨a, m⟩ => g a m b <$> f a m b) init := by
+  simp only [forIn'_eq_foldlM]
+  generalize l.attach = l'
+  induction l' generalizing init <;> simp_all
+
+theorem forIn'_pure_yield_eq_foldl [Monad m] [LawfulMonad m]
+    (l : List α) (f : (a : α) → a ∈ l → β → β) (init : β) :
+    forIn' l init (fun a m b => pure (.yield (f a m b))) =
+      pure (f := m) (l.attach.foldl (fun b ⟨a, h⟩ => f a h b) init) := by
+  simp only [forIn'_eq_foldlM]
+  generalize l.attach = l'
+  induction l' generalizing init <;> simp_all
+
+@[simp] theorem forIn'_yield_eq_foldl
+    (l : List α) (f : (a : α) → a ∈ l → β → β) (init : β) :
+    forIn' (m := Id) l init (fun a m b => .yield (f a m b)) =
+      l.attach.foldl (fun b ⟨a, h⟩ => f a h b) init := by
+  simp only [forIn'_eq_foldlM]
+  generalize l.attach = l'
+  induction l' generalizing init <;> simp_all
+
+/--
+We can express a for loop over a list as a fold,
+in which whenever we reach `.done b` we keep that value through the rest of the fold.
+-/
+theorem forIn_eq_foldlM [Monad m] [LawfulMonad m]
+    (f : α → β → m (ForInStep β)) (init : β) (l : List α) :
+    forIn l init f = ForInStep.value <$>
+      l.foldlM (fun b a => match b with
+        | .yield b => f a b
+        | .done b => pure (.done b)) (ForInStep.yield init) := by
+  induction l generalizing init with
+  | nil => simp
+  | cons a as ih =>
+    simp only [foldlM_cons, bind_pure_comp, forIn_cons, _root_.map_bind]
+    congr 1
+    funext x
+    match x with
+    | .done b =>
+      clear ih
+      dsimp
+      induction as with
+      | nil => simp
+      | cons a as ih => simp [ih]
+    | .yield b =>
+      simp [ih]
+
+/-- We can express a for loop over a list which always yields as a fold. -/
+@[simp] theorem forIn_yield_eq_foldlM [Monad m] [LawfulMonad m]
+    (l : List α) (f : α → β → m γ) (g : α → β → γ → β) (init : β) :
+    forIn l init (fun a b => (fun c => .yield (g a b c)) <$> f a b) =
+      l.foldlM (fun b a => g a b <$> f a b) init := by
+  simp only [forIn_eq_foldlM]
+  induction l generalizing init <;> simp_all
+
+theorem forIn_pure_yield_eq_foldl [Monad m] [LawfulMonad m]
+    (l : List α) (f : α → β → β) (init : β) :
+    forIn l init (fun a b => pure (.yield (f a b))) =
+      pure (f := m) (l.foldl (fun b a => f a b) init) := by
+  simp only [forIn_eq_foldlM]
+  induction l generalizing init <;> simp_all
+
+@[simp] theorem forIn_yield_eq_foldl
+    (l : List α) (f : α → β → β) (init : β) :
+    forIn (m := Id) l init (fun a b => .yield (f a b)) =
+      l.foldl (fun b a => f a b) init := by
+  simp only [forIn_eq_foldlM]
+  induction l generalizing init <;> simp_all
+
+/-! ### allM -/
+
+theorem allM_eq_not_anyM_not [Monad m] [LawfulMonad m] (p : α → m Bool) (as : List α) :
+    allM p as = (! ·) <$> anyM ((! ·) <$> p ·) as := by
+  induction as with
+  | nil => simp
+  | cons a as ih =>
+    simp only [allM, anyM, bind_map_left, _root_.map_bind]
+    congr
+    funext b
+    split <;> simp_all
+
 end List

src/Init/Data/List/Nat.lean

@@ -12,3 +12,6 @@ import Init.Data.List.Nat.TakeDrop
 import Init.Data.List.Nat.Count
 import Init.Data.List.Nat.Erase
 import Init.Data.List.Nat.Find
+import Init.Data.List.Nat.BEq
+import Init.Data.List.Nat.Modify
+import Init.Data.List.Nat.InsertIdx

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

@@ -0,0 +1,47 @@
+/-
+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.Nat.Lemmas
+import Init.Data.List.Basic
+
+namespace List
+
+/-! ### isEqv-/
+
+theorem isEqv_eq_decide (a b : List α) (r) :
+    isEqv a b r = if h : a.length = b.length then
+      decide (∀ (i : Nat) (h' : i < a.length), r (a[i]'(h ▸ h')) (b[i]'(h ▸ h'))) else false := by
+  induction a generalizing b with
+  | nil =>
+    cases b <;> simp
+  | cons a as ih =>
+    cases b with
+    | nil => simp
+    | cons b bs =>
+      simp only [isEqv, ih, length_cons, Nat.add_right_cancel_iff]
+      split <;> simp [Nat.forall_lt_succ_left']
+
+/-! ### beq -/
+
+theorem beq_eq_isEqv [BEq α] (a b : List α) : a.beq b = isEqv a b (· == ·) := by
+  induction a generalizing b with
+  | nil =>
+    cases b <;> simp
+  | cons a as ih =>
+    cases b with
+    | nil => simp
+    | cons b bs =>
+      simp only [beq_cons₂, ih, isEqv_eq_decide, length_cons, Nat.add_right_cancel_iff,
+        Nat.forall_lt_succ_left', getElem_cons_zero, getElem_cons_succ, Bool.decide_and,
+        Bool.decide_eq_true]
+      split <;> simp
+
+theorem beq_eq_decide [BEq α] (a b : List α) :
+    (a == b) = if h : a.length = b.length then
+      decide (∀ (i : Nat) (h' : i < a.length), a[i] == b[i]'(h ▸ h')) else false := by
+  simp [BEq.beq, beq_eq_isEqv, isEqv_eq_decide]
+
+end List

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

@@ -86,164 +86,66 @@ theorem mem_eraseIdx_iff_getElem? {x : α} {l} {k} : x ∈ eraseIdx l k ↔ ∃
     obtain ⟨h', -⟩ := getElem?_eq_some_iff.1 h
     exact ⟨h', h⟩
 
-/-! ### minimum? -/
+/-! ### min? -/
 
--- 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
+-- A specialization of `min?_eq_some_iff` to Nat.
+theorem min?_eq_some_iff' {xs : List Nat} :
+    xs.min? = some a ↔ (a ∈ xs ∧ ∀ b ∈ xs, a ≤ b) :=
+  min?_eq_some_iff
     (le_refl := Nat.le_refl)
-    (min_eq_or := fun _ _ => by omega)
-    (le_min_iff := fun _ _ _ => by omega)
+    (min_eq_or := fun _ _ => Nat.min_def .. ▸ by split <;> simp)
+    (le_min_iff := fun _ _ _ => Nat.le_min)
 
--- 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
-
-theorem foldl_min
-    {α : Type _} [Min α] [Std.IdempotentOp (min : α → α → α)] [Std.Associative (min : α → α → α)]
-    {l : List α} {a : α} :
-    l.foldl (init := a) min = min a (l.minimum?.getD a) := by
-  cases l with
-  | nil => simp [Std.IdempotentOp.idempotent]
-  | cons b l =>
-    simp only [minimum?]
-    induction l generalizing a b with
-    | nil => simp
-    | cons c l ih => simp [ih, Std.Associative.assoc]
-
-theorem foldl_min_right {α β : Type _}
-    [Min β] [Std.IdempotentOp (min : β → β → β)] [Std.Associative (min : β → β → β)]
-    {l : List α} {b : β} {f : α → β} :
-    (l.foldl (init := b) fun acc a => min acc (f a)) = min b ((l.map f).minimum?.getD b) := by
-  rw [← foldl_map, foldl_min]
-
-theorem foldl_min_le {l : List Nat} {a : Nat} : l.foldl (init := a) min ≤ a := by
-  induction l generalizing a with
-  | nil => simp
-  | cons c l ih =>
-    simp only [foldl_cons]
-    exact Nat.le_trans ih (Nat.min_le_left _ _)
-
-theorem foldl_min_min_of_le {l : List Nat} {a b : Nat} (h : a ≤ b) :
-    l.foldl (init := a) min ≤ b :=
-  Nat.le_trans (foldl_min_le) h
-
-theorem minimum?_getD_le_of_mem {l : List Nat} {a k : Nat} (h : a ∈ l) :
-    l.minimum?.getD k ≤ a := by
-  cases l with
+theorem min?_get_le_of_mem {l : List Nat} {a : Nat} (h : a ∈ l) :
+    l.min?.get (isSome_min?_of_mem h) ≤ a := by
+  induction l with
   | nil => simp at h
-  | cons b l =>
-    simp [minimum?_cons]
-    simp at h
-    rcases h with (rfl | h)
-    · exact foldl_min_le
-    · induction l generalizing b with
-      | nil => simp_all
-      | cons c l ih =>
-        simp only [foldl_cons]
-        simp at h
-        rcases h with (rfl | h)
-        · exact foldl_min_min_of_le (Nat.min_le_right _ _)
-        · exact ih _ h
+  | cons b t ih =>
+    simp only [min?_cons, Option.get_some] at ih ⊢
+    rcases mem_cons.1 h with (rfl|h)
+    · cases t.min? with
+      | none => simp
+      | some b => simpa using Nat.min_le_left _ _
+    · obtain ⟨q, hq⟩ := Option.isSome_iff_exists.1 (isSome_min?_of_mem h)
+      simp only [hq, Option.elim_some] at ih ⊢
+      exact Nat.le_trans (Nat.min_le_right _ _) (ih h)
 
-/-! ### maximum? -/
+theorem min?_getD_le_of_mem {l : List Nat} {a k : Nat} (h : a ∈ l) : l.min?.getD k ≤ a :=
+  Option.get_eq_getD _ ▸ min?_get_le_of_mem h
 
--- 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
+/-! ### max? -/
+
+-- A specialization of `max?_eq_some_iff` to Nat.
+theorem max?_eq_some_iff' {xs : List Nat} :
+    xs.max? = some a ↔ (a ∈ xs ∧ ∀ b ∈ xs, b ≤ a) :=
+  max?_eq_some_iff
     (le_refl := Nat.le_refl)
-    (max_eq_or := fun _ _ => by omega)
-    (max_le_iff := fun _ _ _ => by omega)
+    (max_eq_or := fun _ _ => Nat.max_def .. ▸ by split <;> simp)
+    (max_le_iff := fun _ _ _ => Nat.max_le)
 
--- 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
-
-theorem foldl_max
-    {α : Type _} [Max α] [Std.IdempotentOp (max : α → α → α)] [Std.Associative (max : α → α → α)]
-    {l : List α} {a : α} :
-    l.foldl (init := a) max = max a (l.maximum?.getD a) := by
-  cases l with
-  | nil => simp [Std.IdempotentOp.idempotent]
-  | cons b l =>
-    simp only [maximum?]
-    induction l generalizing a b with
-    | nil => simp
-    | cons c l ih => simp [ih, Std.Associative.assoc]
-
-theorem foldl_max_right {α β : Type _}
-    [Max β] [Std.IdempotentOp (max : β → β → β)] [Std.Associative (max : β → β → β)]
-    {l : List α} {b : β} {f : α → β} :
-    (l.foldl (init := b) fun acc a => max acc (f a)) = max b ((l.map f).maximum?.getD b) := by
-  rw [← foldl_map, foldl_max]
-
-theorem le_foldl_max {l : List Nat} {a : Nat} : a ≤ l.foldl (init := a) max := by
-  induction l generalizing a with
-  | nil => simp
-  | cons c l ih =>
-    simp only [foldl_cons]
-    exact Nat.le_trans (Nat.le_max_left _ _) ih
-
-theorem le_foldl_max_of_le {l : List Nat} {a b : Nat} (h : a ≤ b) :
-    a ≤ l.foldl (init := b) max :=
-  Nat.le_trans h (le_foldl_max)
-
-theorem le_maximum?_getD_of_mem {l : List Nat} {a k : Nat} (h : a ∈ l) :
-    a ≤ l.maximum?.getD k := by
-  cases l with
+theorem le_max?_get_of_mem {l : List Nat} {a : Nat} (h : a ∈ l) :
+    a ≤ l.max?.get (isSome_max?_of_mem h) := by
+  induction l with
   | nil => simp at h
-  | cons b l =>
-    simp [maximum?_cons]
-    simp at h
-    rcases h with (rfl | h)
-    · exact le_foldl_max
-    · induction l generalizing b with
-      | nil => simp_all
-      | cons c l ih =>
-        simp only [foldl_cons]
-        simp at h
-        rcases h with (rfl | h)
-        · exact le_foldl_max_of_le (Nat.le_max_right b a)
-        · exact ih _ h
+  | cons b t ih =>
+    simp only [max?_cons, Option.get_some] at ih ⊢
+    rcases mem_cons.1 h with (rfl|h)
+    · cases t.max? with
+      | none => simp
+      | some b => simpa using Nat.le_max_left _ _
+    · obtain ⟨q, hq⟩ := Option.isSome_iff_exists.1 (isSome_max?_of_mem h)
+      simp only [hq, Option.elim_some] at ih ⊢
+      exact Nat.le_trans (ih h) (Nat.le_max_right _ _)
+
+theorem le_max?_getD_of_mem {l : List Nat} {a k : Nat} (h : a ∈ l) :
+    a ≤ l.max?.getD k :=
+  Option.get_eq_getD _ ▸ le_max?_get_of_mem h
+
+@[deprecated min?_eq_some_iff' (since := "2024-09-29")] abbrev minimum?_eq_some_iff' := @min?_eq_some_iff'
+@[deprecated min?_cons' (since := "2024-09-29")] abbrev minimum?_cons' := @min?_cons'
+@[deprecated min?_getD_le_of_mem (since := "2024-09-29")] abbrev minimum?_getD_le_of_mem := @min?_getD_le_of_mem
+@[deprecated max?_eq_some_iff' (since := "2024-09-29")] abbrev maximum?_eq_some_iff' := @max?_eq_some_iff'
+@[deprecated max?_cons' (since := "2024-09-29")] abbrev maximum?_cons' := @max?_cons'
+@[deprecated le_max?_getD_of_mem (since := "2024-09-29")] abbrev le_maximum?_getD_of_mem := @le_max?_getD_of_mem
 
 end List

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

@@ -10,7 +10,7 @@ import Init.Data.List.Erase
 namespace List
 
 theorem getElem?_eraseIdx (l : List α) (i : Nat) (j : Nat) :
-    (l.eraseIdx i)[j]? = if h : j < i then l[j]? else l[j + 1]? := by
+    (l.eraseIdx i)[j]? = if j < i then l[j]? else l[j + 1]? := by
   rw [eraseIdx_eq_take_drop_succ, getElem?_append]
   split <;> rename_i h
   · rw [getElem?_take]
@@ -64,3 +64,82 @@ theorem getElem_eraseIdx_of_ge (l : List α) (i : Nat) (j : Nat) (h : j < (l.era
     (l.eraseIdx i)[j] = l[j + 1]'(by rw [length_eraseIdx] at h; split at h <;> omega) := by
   rw [getElem_eraseIdx, dif_neg]
   omega
+
+theorem eraseIdx_set_eq {l : List α} {i : Nat} {a : α} :
+    (l.set i a).eraseIdx i = l.eraseIdx i := by
+  apply ext_getElem
+  · simp [length_eraseIdx]
+  · intro n h₁ h₂
+    rw [getElem_eraseIdx, getElem_eraseIdx]
+    split <;>
+    · rw [getElem_set_ne]
+      omega
+
+theorem eraseIdx_set_lt {l : List α} {i : Nat} {j : Nat} {a : α} (h : j < i) :
+    (l.set i a).eraseIdx j = (l.eraseIdx j).set (i - 1) a := by
+  apply ext_getElem
+  · simp [length_eraseIdx]
+  · intro n h₁ h₂
+    simp only [length_eraseIdx, length_set] at h₁
+    simp only [getElem_eraseIdx, getElem_set]
+    split
+    · split
+      · split
+        · rfl
+        · omega
+      · split
+        · omega
+        · rfl
+    · split
+      · split
+        · rfl
+        · omega
+      · have t : i - 1 ≠ n := by omega
+        simp [t]
+
+theorem eraseIdx_set_gt {l : List α} {i : Nat} {j : Nat} {a : α} (h : i < j) :
+    (l.set i a).eraseIdx j = (l.eraseIdx j).set i a := by
+  apply ext_getElem
+  · simp [length_eraseIdx]
+  · intro n h₁ h₂
+    simp only [length_eraseIdx, length_set] at h₁
+    simp only [getElem_eraseIdx, getElem_set]
+    split
+    · rfl
+    · split
+      · split
+        · rfl
+        · omega
+      · have t : i ≠ n := by omega
+        simp [t]
+
+@[simp] theorem set_getElem_succ_eraseIdx_succ
+    {l : List α} {i : Nat} (h : i + 1 < l.length) :
+    (l.eraseIdx (i + 1)).set i l[i + 1] = l.eraseIdx i := by
+  apply ext_getElem
+  · simp only [length_set, length_eraseIdx, h, ↓reduceIte]
+    rw [if_pos]
+    omega
+  · intro n h₁ h₂
+    simp [getElem_set, getElem_eraseIdx]
+    split
+    · split
+      · omega
+      · simp_all
+    · split
+      · split
+        · rfl
+        · omega
+      · have t : ¬ n < i := by omega
+        simp [t]
+
+@[simp] theorem eraseIdx_length_sub_one (l : List α) :
+    (l.eraseIdx (l.length - 1)) = l.dropLast := by
+  apply ext_getElem
+  · simp [length_eraseIdx]
+    omega
+  · intro n h₁ h₂
+    rw [getElem_eraseIdx_of_lt, getElem_dropLast]
+    simp_all
+
+end List

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

@@ -9,6 +9,32 @@ import Init.Data.List.Find
 
 namespace List
 
+open Nat
+
+theorem find?_eq_some_iff_getElem {xs : List α} {p : α → Bool} {b : α} :
+    xs.find? p = some b ↔ p b ∧ ∃ i h, xs[i] = b ∧ ∀ j : Nat, (hj : j < i) → !p xs[j] := by
+  rw [find?_eq_some_iff_append]
+  simp only [Bool.not_eq_eq_eq_not, Bool.not_true, exists_and_right, and_congr_right_iff]
+  intro w
+  constructor
+  · rintro ⟨as, ⟨bs, rfl⟩, h⟩
+    refine ⟨as.length, ⟨?_, ?_, ?_⟩⟩
+    · simp only [length_append, length_cons]
+      refine Nat.lt_add_of_pos_right (zero_lt_succ bs.length)
+    · rw [getElem_append_right (Nat.le_refl as.length)]
+      simp
+    · intro j h'
+      rw [getElem_append_left h']
+      exact h _ (getElem_mem h')
+  · rintro ⟨i, h, rfl, h'⟩
+    refine ⟨xs.take i, ⟨xs.drop (i+1), ?_⟩, ?_⟩
+    · rw [getElem_cons_drop, take_append_drop]
+    · intro a m
+      rw [mem_take_iff_getElem] at m
+      obtain ⟨j, h, rfl⟩ := m
+      apply h'
+      omega
+
 theorem findIdx?_eq_some_le_of_findIdx?_eq_some {xs : List α} {p q : α → Bool} (w : ∀ x ∈ xs, p x → q x) {i : Nat}
     (h : xs.findIdx? p = some i) : ∃ j, j ≤ i ∧ xs.findIdx? q = some j := by
   simp only [findIdx?_eq_findSome?_enum] at h

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

@@ -0,0 +1,242 @@
+/-
+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.Modify
+
+/-!
+# insertIdx
+
+Proves various lemmas about `List.insertIdx`.
+-/
+
+open Function
+
+open Nat
+
+namespace List
+
+universe u
+
+variable {α : Type u}
+
+section InsertIdx
+
+variable {a : α}
+
+@[simp]
+theorem insertIdx_zero (s : List α) (x : α) : insertIdx 0 x s = x :: s :=
+  rfl
+
+@[simp]
+theorem insertIdx_succ_nil (n : Nat) (a : α) : insertIdx (n + 1) a [] = [] :=
+  rfl
+
+@[simp]
+theorem insertIdx_succ_cons (s : List α) (hd x : α) (n : Nat) :
+    insertIdx (n + 1) x (hd :: s) = hd :: insertIdx n x s :=
+  rfl
+
+theorem length_insertIdx : ∀ n as, (insertIdx n a as).length = if n ≤ as.length then as.length + 1 else as.length
+  | 0, _ => by simp
+  | n + 1, [] => by simp
+  | n + 1, a :: as => by
+    simp only [insertIdx_succ_cons, length_cons, length_insertIdx, Nat.add_le_add_iff_right]
+    split <;> rfl
+
+theorem length_insertIdx_of_le_length (h : n ≤ length as) : length (insertIdx n a as) = length as + 1 := by
+  simp [length_insertIdx, h]
+
+theorem length_insertIdx_of_length_lt (h : length as < n) : length (insertIdx n a as) = length as := by
+  simp [length_insertIdx, h]
+
+theorem eraseIdx_insertIdx (n : Nat) (l : List α) : (l.insertIdx n a).eraseIdx n = l := by
+  rw [eraseIdx_eq_modifyTailIdx, insertIdx, modifyTailIdx_modifyTailIdx_self]
+  exact modifyTailIdx_id _ _
+
+theorem insertIdx_eraseIdx_of_ge :
+    ∀ n m as,
+      n < length as → n ≤ m → insertIdx m a (as.eraseIdx n) = (as.insertIdx (m + 1) a).eraseIdx n
+  | 0, 0, [], has, _ => (Nat.lt_irrefl _ has).elim
+  | 0, 0, _ :: as, _, _ => by simp [eraseIdx, insertIdx]
+  | 0, _ + 1, _ :: _, _, _ => rfl
+  | n + 1, m + 1, a :: as, has, hmn =>
+    congrArg (cons a) <|
+      insertIdx_eraseIdx_of_ge n m as (Nat.lt_of_succ_lt_succ has) (Nat.le_of_succ_le_succ hmn)
+
+theorem insertIdx_eraseIdx_of_le :
+    ∀ n m as,
+      n < length as → m ≤ n → insertIdx m a (as.eraseIdx n) = (as.insertIdx m a).eraseIdx (n + 1)
+  | _, 0, _ :: _, _, _ => rfl
+  | n + 1, m + 1, a :: as, has, hmn =>
+    congrArg (cons a) <|
+      insertIdx_eraseIdx_of_le n m as (Nat.lt_of_succ_lt_succ has) (Nat.le_of_succ_le_succ hmn)
+
+theorem insertIdx_comm (a b : α) :
+    ∀ (i j : Nat) (l : List α) (_ : i ≤ j) (_ : j ≤ length l),
+      (l.insertIdx i a).insertIdx (j + 1) b = (l.insertIdx j b).insertIdx i a
+  | 0, j, l => by simp [insertIdx]
+  | _ + 1, 0, _ => fun h => (Nat.not_lt_zero _ h).elim
+  | i + 1, j + 1, [] => by simp
+  | i + 1, j + 1, c :: l => fun h₀ h₁ => by
+    simp only [insertIdx_succ_cons, cons.injEq, true_and]
+    exact insertIdx_comm a b i j l (Nat.le_of_succ_le_succ h₀) (Nat.le_of_succ_le_succ h₁)
+
+theorem mem_insertIdx {a b : α} :
+    ∀ {n : Nat} {l : List α} (_ : n ≤ l.length), a ∈ l.insertIdx n b ↔ a = b ∨ a ∈ l
+  | 0, as, _ => by simp
+  | _ + 1, [], h => (Nat.not_succ_le_zero _ h).elim
+  | n + 1, a' :: as, h => by
+    rw [List.insertIdx_succ_cons, mem_cons, mem_insertIdx (Nat.le_of_succ_le_succ h),
+      ← or_assoc, @or_comm (a = a'), or_assoc, mem_cons]
+
+theorem insertIdx_of_length_lt (l : List α) (x : α) (n : Nat) (h : l.length < n) :
+    insertIdx n x l = l := by
+  induction l generalizing n with
+  | nil =>
+    cases n
+    · simp at h
+    · simp
+  | cons x l ih =>
+    cases n
+    · simp at h
+    · simp only [Nat.succ_lt_succ_iff, length] at h
+      simpa using ih _ h
+
+@[simp]
+theorem insertIdx_length_self (l : List α) (x : α) : insertIdx l.length x l = l ++ [x] := by
+  induction l with
+  | nil => simp
+  | cons x l ih => simpa using ih
+
+theorem length_le_length_insertIdx (l : List α) (x : α) (n : Nat) :
+    l.length ≤ (insertIdx n x l).length := by
+  simp only [length_insertIdx]
+  split <;> simp
+
+theorem length_insertIdx_le_succ (l : List α) (x : α) (n : Nat) :
+    (insertIdx n x l).length ≤ l.length + 1 := by
+  simp only [length_insertIdx]
+  split <;> simp
+
+theorem getElem_insertIdx_of_lt {l : List α} {x : α} {n k : Nat} (hn : k < n)
+    (hk : k < (insertIdx n x l).length) :
+    (insertIdx n x l)[k] = l[k]'(by simp [length_insertIdx] at hk; split at hk <;> omega) := by
+  induction n generalizing k l with
+  | zero => simp at hn
+  | succ n ih =>
+    cases l with
+    | nil => simp
+    | cons _ _=>
+      cases k
+      · simp [get]
+      · rw [Nat.succ_lt_succ_iff] at hn
+        simpa using ih hn _
+
+@[simp]
+theorem getElem_insertIdx_self {l : List α} {x : α} {n : Nat} (hn : n < (insertIdx n x l).length) :
+    (insertIdx n x l)[n] = x := by
+  induction l generalizing n with
+  | nil =>
+    simp [length_insertIdx] at hn
+    split at hn
+    · simp_all
+    · omega
+  | cons _ _ ih =>
+    cases n
+    · simp
+    · simp only [insertIdx_succ_cons, length_cons, length_insertIdx, Nat.add_lt_add_iff_right] at hn ih
+      simpa using ih hn
+
+theorem getElem_insertIdx_of_ge {l : List α} {x : α} {n k : Nat} (hn : n + 1 ≤ k)
+    (hk : k < (insertIdx n x l).length) :
+    (insertIdx n x l)[k] = l[k - 1]'(by simp [length_insertIdx] at hk; split at hk <;> omega) := by
+  induction l generalizing n k with
+  | nil =>
+    cases n with
+    | zero =>
+      simp only [insertIdx_zero, length_singleton, lt_one_iff] at hk
+      omega
+    | succ n => simp at hk
+  | cons _ _ ih =>
+    cases n with
+    | zero =>
+      simp only [insertIdx_zero] at hk
+      cases k with
+      | zero => omega
+      | succ k => simp
+    | succ n =>
+      cases k with
+      | zero => simp
+      | succ k =>
+        simp only [insertIdx_succ_cons, getElem_cons_succ]
+        rw [ih (by omega)]
+        cases k with
+        | zero => omega
+        | succ k => simp
+
+theorem getElem_insertIdx {l : List α} {x : α} {n k : Nat} (h : k < (insertIdx n x l).length) :
+    (insertIdx n x l)[k] =
+      if h₁ : k < n then
+        l[k]'(by simp [length_insertIdx] at h; split at h <;> omega)
+      else
+        if h₂ : k = n then
+          x
+        else
+          l[k-1]'(by simp [length_insertIdx] at h; split at h <;> omega) := by
+  split <;> rename_i h₁
+  · rw [getElem_insertIdx_of_lt h₁]
+  · split <;> rename_i h₂
+    · subst h₂
+      rw [getElem_insertIdx_self h]
+    · rw [getElem_insertIdx_of_ge (by omega)]
+
+theorem getElem?_insertIdx {l : List α} {x : α} {n k : Nat} :
+    (insertIdx n x l)[k]? =
+      if k < n then
+        l[k]?
+      else
+        if k = n then
+          if k ≤ l.length then some x else none
+        else
+          l[k-1]? := by
+  rw [getElem?_def]
+  split <;> rename_i h
+  · rw [getElem_insertIdx h]
+    simp only [length_insertIdx] at h
+    split <;> rename_i h₁
+    · rw [getElem?_def, dif_pos]
+    · split <;> rename_i h₂
+      · rw [if_pos]
+        split at h <;> omega
+      · rw [getElem?_def]
+        simp only [Option.some_eq_dite_none_right, exists_prop, and_true]
+        split at h <;> omega
+  · simp only [length_insertIdx] at h
+    split <;> rename_i h₁
+    · rw [getElem?_eq_none]
+      split at h <;> omega
+    · split <;> rename_i h₂
+      · rw [if_neg]
+        split at h <;> omega
+      · rw [getElem?_eq_none]
+        split at h <;> omega
+
+theorem getElem?_insertIdx_of_lt {l : List α} {x : α} {n k : Nat} (h : k < n) :
+    (insertIdx n x l)[k]? = l[k]? := by
+  rw [getElem?_insertIdx, if_pos h]
+
+theorem getElem?_insertIdx_self {l : List α} {x : α} {n : Nat} :
+    (insertIdx n x l)[n]? = if n ≤ l.length then some x else none := by
+  rw [getElem?_insertIdx, if_neg (by omega)]
+  simp
+
+theorem getElem?_insertIdx_of_ge {l : List α} {x : α} {n k : Nat} (h : n + 1 ≤ k) :
+    (insertIdx n x l)[k]? = l[k - 1]? := by
+  rw [getElem?_insertIdx, if_neg (by omega), if_neg (by omega)]
+
+end InsertIdx
+
+end List

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

@@ -0,0 +1,314 @@
+/-
+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.Nat.Erase
+
+namespace List
+
+/-! ### modifyHead -/
+
+@[simp] theorem length_modifyHead {f : α → α} {l : List α} : (l.modifyHead f).length = l.length := by
+  cases l <;> simp [modifyHead]
+
+theorem modifyHead_eq_set [Inhabited α] (f : α → α) (l : List α) :
+    l.modifyHead f = l.set 0 (f (l[0]?.getD default)) := by cases l <;> simp [modifyHead]
+
+@[simp] theorem modifyHead_eq_nil_iff {f : α → α} {l : List α} :
+    l.modifyHead f = [] ↔ l = [] := by cases l <;> simp [modifyHead]
+
+@[simp] theorem modifyHead_modifyHead {l : List α} {f g : α → α} :
+    (l.modifyHead f).modifyHead g = l.modifyHead (g ∘ f) := by cases l <;> simp [modifyHead]
+
+theorem getElem_modifyHead {l : List α} {f : α → α} {n} (h : n < (l.modifyHead f).length) :
+    (l.modifyHead f)[n] = if h' : n = 0 then f (l[0]'(by simp at h; omega)) else l[n]'(by simpa using h) := by
+  cases l with
+  | nil => simp at h
+  | cons hd tl => cases n <;> simp
+
+@[simp] theorem getElem_modifyHead_zero {l : List α} {f : α → α} {h} :
+    (l.modifyHead f)[0] = f (l[0]'(by simpa using h)) := by simp [getElem_modifyHead]
+
+@[simp] theorem getElem_modifyHead_succ {l : List α} {f : α → α} {n} (h : n + 1 < (l.modifyHead f).length) :
+    (l.modifyHead f)[n + 1] = l[n + 1]'(by simpa using h) := by simp [getElem_modifyHead]
+
+theorem getElem?_modifyHead {l : List α} {f : α → α} {n} :
+    (l.modifyHead f)[n]? = if n = 0 then l[n]?.map f else l[n]? := by
+  cases l with
+  | nil => simp
+  | cons hd tl => cases n <;> simp
+
+@[simp] theorem getElem?_modifyHead_zero {l : List α} {f : α → α} :
+    (l.modifyHead f)[0]? = l[0]?.map f := by simp [getElem?_modifyHead]
+
+@[simp] theorem getElem?_modifyHead_succ {l : List α} {f : α → α} {n} :
+    (l.modifyHead f)[n + 1]? = l[n + 1]? := by simp [getElem?_modifyHead]
+
+@[simp] theorem head_modifyHead (f : α → α) (l : List α) (h) :
+    (l.modifyHead f).head h = f (l.head (by simpa using h)) := by
+  cases l with
+  | nil => simp at h
+  | cons hd tl => simp
+
+@[simp] theorem head?_modifyHead {l : List α} {f : α → α} :
+    (l.modifyHead f).head? = l.head?.map f := by cases l <;> simp
+
+@[simp] theorem tail_modifyHead {f : α → α} {l : List α} :
+    (l.modifyHead f).tail = l.tail := by cases l <;> simp
+
+@[simp] theorem take_modifyHead {f : α → α} {l : List α} {n} :
+    (l.modifyHead f).take n = (l.take n).modifyHead f := by
+  cases l <;> cases n <;> simp
+
+@[simp] theorem drop_modifyHead_of_pos {f : α → α} {l : List α} {n} (h : 0 < n) :
+    (l.modifyHead f).drop n = l.drop n := by
+  cases l <;> cases n <;> simp_all
+
+@[simp] theorem eraseIdx_modifyHead_zero {f : α → α} {l : List α} :
+    (l.modifyHead f).eraseIdx 0 = l.eraseIdx 0 := by cases l <;> simp
+
+@[simp] theorem eraseIdx_modifyHead_of_pos {f : α → α} {l : List α} {n} (h : 0 < n) :
+    (l.modifyHead f).eraseIdx n = (l.eraseIdx n).modifyHead f := by cases l <;> cases n <;> simp_all
+
+@[simp] theorem modifyHead_id : modifyHead (id : α → α) = id := by funext l; cases l <;> simp
+
+/-! ### modifyTailIdx -/
+
+@[simp] theorem modifyTailIdx_id : ∀ n (l : List α), l.modifyTailIdx id n = l
+  | 0, _ => rfl
+  | _+1, [] => rfl
+  | n+1, a :: l => congrArg (cons a) (modifyTailIdx_id n l)
+
+theorem eraseIdx_eq_modifyTailIdx : ∀ n (l : List α), eraseIdx l n = modifyTailIdx tail n l
+  | 0, l => by cases l <;> rfl
+  | _+1, [] => rfl
+  | _+1, _ :: _ => congrArg (cons _) (eraseIdx_eq_modifyTailIdx _ _)
+
+@[simp] theorem length_modifyTailIdx (f : List α → List α) (H : ∀ l, length (f l) = length l) :
+    ∀ n l, length (modifyTailIdx f n l) = length l
+  | 0, _ => H _
+  | _+1, [] => rfl
+  | _+1, _ :: _ => congrArg (·+1) (length_modifyTailIdx _ H _ _)
+
+theorem modifyTailIdx_add (f : List α → List α) (n) (l₁ l₂ : List α) :
+    modifyTailIdx f (l₁.length + n) (l₁ ++ l₂) = l₁ ++ modifyTailIdx f n l₂ := by
+  induction l₁ <;> simp [*, Nat.succ_add]
+
+theorem modifyTailIdx_eq_take_drop (f : List α → List α) (H : f [] = []) :
+    ∀ n l, modifyTailIdx f n l = take n l ++ f (drop n l)
+  | 0, _ => rfl
+  | _ + 1, [] => H.symm
+  | n + 1, b :: l => congrArg (cons b) (modifyTailIdx_eq_take_drop f H n l)
+
+theorem exists_of_modifyTailIdx (f : List α → List α) {n} {l : List α} (h : n ≤ l.length) :
+    ∃ l₁ l₂, l = l₁ ++ l₂ ∧ l₁.length = n ∧ modifyTailIdx f n l = l₁ ++ f l₂ :=
+  have ⟨_, _, eq, hl⟩ : ∃ l₁ l₂, l = l₁ ++ l₂ ∧ l₁.length = n :=
+    ⟨_, _, (take_append_drop n l).symm, length_take_of_le h⟩
+  ⟨_, _, eq, hl, hl ▸ eq ▸ modifyTailIdx_add (n := 0) ..⟩
+
+theorem modifyTailIdx_modifyTailIdx {f g : List α → List α} (m : Nat) :
+    ∀ (n) (l : List α),
+      (l.modifyTailIdx f n).modifyTailIdx g (m + n) =
+        l.modifyTailIdx (fun l => (f l).modifyTailIdx g m) n
+  | 0, _ => rfl
+  | _ + 1, [] => rfl
+  | n + 1, a :: l => congrArg (List.cons a) (modifyTailIdx_modifyTailIdx m n l)
+
+theorem modifyTailIdx_modifyTailIdx_le {f g : List α → List α} (m n : Nat) (l : List α)
+    (h : n ≤ m) :
+    (l.modifyTailIdx f n).modifyTailIdx g m =
+      l.modifyTailIdx (fun l => (f l).modifyTailIdx g (m - n)) n := by
+  rcases Nat.exists_eq_add_of_le h with ⟨m, rfl⟩
+  rw [Nat.add_comm, modifyTailIdx_modifyTailIdx, Nat.add_sub_cancel]
+
+theorem modifyTailIdx_modifyTailIdx_self {f g : List α → List α} (n : Nat) (l : List α) :
+    (l.modifyTailIdx f n).modifyTailIdx g n = l.modifyTailIdx (g ∘ f) n := by
+  rw [modifyTailIdx_modifyTailIdx_le n n l (Nat.le_refl n), Nat.sub_self]; rfl
+
+/-! ### modify -/
+
+@[simp] theorem modify_nil (f : α → α) (n) : [].modify f n = [] := by cases n <;> rfl
+
+@[simp] theorem modify_zero_cons (f : α → α) (a : α) (l : List α) :
+    (a :: l).modify f 0 = f a :: l := rfl
+
+@[simp] theorem modify_succ_cons (f : α → α) (a : α) (l : List α) (n) :
+    (a :: l).modify f (n + 1) = a :: l.modify f n := by rfl
+
+theorem modifyHead_eq_modify_zero (f : α → α) (l : List α) :
+    l.modifyHead f = l.modify f 0 := by cases l <;> simp
+
+@[simp] theorem modify_eq_nil_iff (f : α → α) (n) (l : List α) :
+    l.modify f n = [] ↔ l = [] := by cases l <;> cases n <;> simp
+
+theorem getElem?_modify (f : α → α) :
+    ∀ n (l : List α) m, (modify f n l)[m]? = (fun a => if n = m then f a else a) <$> l[m]?
+  | n, l, 0 => by cases l <;> cases n <;> simp
+  | n, [], _+1 => by cases n <;> rfl
+  | 0, _ :: l, m+1 => by cases h : l[m]? <;> simp [h, modify, m.succ_ne_zero.symm]
+  | n+1, a :: l, m+1 => by
+    simp only [modify_succ_cons, getElem?_cons_succ, Nat.reduceEqDiff, Option.map_eq_map]
+    refine (getElem?_modify f n l m).trans ?_
+    cases h' : l[m]? <;> by_cases h : n = m <;>
+      simp [h, if_pos, if_neg, Option.map, mt Nat.succ.inj, not_false_iff, h']
+
+@[simp] theorem length_modify (f : α → α) : ∀ n l, length (modify f n l) = length l :=
+  length_modifyTailIdx _ fun l => by cases l <;> rfl
+
+@[simp] theorem getElem?_modify_eq (f : α → α) (n) (l : List α) :
+    (modify f n l)[n]? = f <$> l[n]? := by
+  simp only [getElem?_modify, if_pos]
+
+@[simp] theorem getElem?_modify_ne (f : α → α) {m n} (l : List α) (h : m ≠ n) :
+    (modify f m l)[n]? = l[n]? := by
+  simp only [getElem?_modify, if_neg h, id_map']
+
+theorem getElem_modify (f : α → α) (n) (l : List α) (m) (h : m < (modify f n l).length) :
+    (modify f n l)[m] =
+      if n = m then f (l[m]'(by simp at h; omega)) else l[m]'(by simp at h; omega) := by
+  rw [getElem_eq_iff, getElem?_modify]
+  simp at h
+  simp [h]
+
+@[simp] theorem getElem_modify_eq (f : α → α) (n) (l : List α) (h) :
+    (modify f n l)[n] = f (l[n]'(by simpa using h)) := by simp [getElem_modify]
+
+@[simp] theorem getElem_modify_ne (f : α → α) {m n} (l : List α) (h : m ≠ n) (h') :
+    (modify f m l)[n] = l[n]'(by simpa using h') := by simp [getElem_modify, h]
+
+theorem modify_eq_self {f : α → α} {n} {l : List α} (h : l.length ≤ n) :
+    l.modify f n = l := by
+  apply ext_getElem
+  · simp
+  · intro m h₁ h₂
+    simp only [getElem_modify, ite_eq_right_iff]
+    intro h
+    omega
+
+theorem modify_modify_eq (f g : α → α) (n) (l : List α) :
+    (modify f n l).modify g n = modify (g ∘ f) n l := by
+  apply ext_getElem
+  · simp
+  · intro m h₁ h₂
+    simp only [getElem_modify, Function.comp_apply]
+    split <;> simp
+
+theorem modify_modify_ne (f g : α → α) {m n} (l : List α) (h : m ≠ n) :
+    (modify f m l).modify g n = (l.modify g n).modify f m := by
+  apply ext_getElem
+  · simp
+  · intro m' h₁ h₂
+    simp only [getElem_modify, getElem_modify_ne, h₂]
+    split <;> split <;> first | rfl | omega
+
+theorem modify_eq_set [Inhabited α] (f : α → α) (n) (l : List α) :
+    modify f n l = l.set n (f (l[n]?.getD default)) := by
+  apply ext_getElem
+  · simp
+  · intro m h₁ h₂
+    simp [getElem_modify, getElem_set, h₂]
+    split <;> rename_i h
+    · subst h
+      simp only [length_modify] at h₁
+      simp [h₁]
+    · rfl
+
+theorem modify_eq_take_drop (f : α → α) :
+    ∀ n l, modify f n l = take n l ++ modifyHead f (drop n l) :=
+  modifyTailIdx_eq_take_drop _ rfl
+
+theorem modify_eq_take_cons_drop {f : α → α} {n} {l : List α} (h : n < l.length) :
+    modify f n l = take n l ++ f l[n] :: drop (n + 1) l := by
+  rw [modify_eq_take_drop, drop_eq_getElem_cons h]; rfl
+
+theorem exists_of_modify (f : α → α) {n} {l : List α} (h : n < l.length) :
+    ∃ l₁ a l₂, l = l₁ ++ a :: l₂ ∧ l₁.length = n ∧ modify f n l = l₁ ++ f a :: l₂ :=
+  match exists_of_modifyTailIdx _ (Nat.le_of_lt h) with
+  | ⟨_, _::_, eq, hl, H⟩ => ⟨_, _, _, eq, hl, H⟩
+  | ⟨_, [], eq, hl, _⟩ => nomatch Nat.ne_of_gt h (eq ▸ append_nil _ ▸ hl)
+
+@[simp] theorem modify_id (n) (l : List α) : l.modify id n = l := by
+  simp [modify]
+
+theorem take_modify (f : α → α) (n m) (l : List α) :
+    (modify f m l).take n = (take n l).modify f m := by
+  induction n generalizing l m with
+  | zero => simp
+  | succ n ih =>
+    cases l with
+    | nil => simp
+    | cons hd tl =>
+      cases m with
+      | zero => simp
+      | succ m => simp [ih]
+
+theorem drop_modify_of_lt (f : α → α) (n m) (l : List α) (h : n < m) :
+    (modify f n l).drop m = l.drop m := by
+  apply ext_getElem
+  · simp
+  · intro m' h₁ h₂
+    simp only [getElem_drop, getElem_modify, ite_eq_right_iff]
+    intro h'
+    omega
+
+theorem drop_modify_of_ge (f : α → α) (n m) (l : List α) (h : n ≥ m) :
+    (modify f n l).drop m = modify f (n - m) (drop m l) := by
+  apply ext_getElem
+  · simp
+  · intro m' h₁ h₂
+    simp [getElem_drop, getElem_modify, ite_eq_right_iff]
+    split <;> split <;> first | rfl | omega
+
+theorem eraseIdx_modify_of_eq (f : α → α) (n) (l : List α) :
+    (modify f n l).eraseIdx n = l.eraseIdx n := by
+  apply ext_getElem
+  · simp [length_eraseIdx]
+  · intro m h₁ h₂
+    simp only [getElem_eraseIdx, getElem_modify]
+    split <;> split <;> first | rfl | omega
+
+theorem eraseIdx_modify_of_lt (f : α → α) (i j) (l : List α) (h : j < i) :
+    (modify f i l).eraseIdx j = (l.eraseIdx j).modify f (i - 1) := by
+  apply ext_getElem
+  · simp [length_eraseIdx]
+  · intro k h₁ h₂
+    simp only [getElem_eraseIdx, getElem_modify]
+    by_cases h' : i - 1 = k
+    repeat' split
+    all_goals (first | rfl | omega)
+
+theorem eraseIdx_modify_of_gt (f : α → α) (i j) (l : List α) (h : j > i) :
+    (modify f i l).eraseIdx j = (l.eraseIdx j).modify f i := by
+  apply ext_getElem
+  · simp [length_eraseIdx]
+  · intro k h₁ h₂
+    simp only [getElem_eraseIdx, getElem_modify]
+    by_cases h' : i = k
+    repeat' split
+    all_goals (first | rfl | omega)
+
+theorem modify_eraseIdx_of_lt (f : α → α) (i j) (l : List α) (h : j < i) :
+    (l.eraseIdx i).modify f j = (l.modify f j).eraseIdx i := by
+  apply ext_getElem
+  · simp [length_eraseIdx]
+  · intro k h₁ h₂
+    simp only [getElem_eraseIdx, getElem_modify]
+    by_cases h' : j = k + 1
+    repeat' split
+    all_goals (first | rfl | omega)
+
+theorem modify_eraseIdx_of_ge (f : α → α) (i j) (l : List α) (h : j ≥ i) :
+    (l.eraseIdx i).modify f j = (l.modify f (j + 1)).eraseIdx i := by
+  apply ext_getElem
+  · simp [length_eraseIdx]
+  · intro k h₁ h₂
+    simp only [getElem_eraseIdx, getElem_modify]
+    by_cases h' : j + 1 = k + 1
+    repeat' split
+    all_goals (first | rfl | omega)
+
+end List

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

@@ -108,7 +108,7 @@ theorem range'_eq_append_iff : range' s n = xs ++ ys ↔ ∃ k, k ≤ n ∧ xs =
 
 @[simp] theorem find?_range'_eq_some {s n : Nat} {i : Nat} {p : Nat → Bool} :
     (range' s n).find? p = some i ↔ p i ∧ i ∈ range' s n ∧ ∀ j, s ≤ j → j < i → !p j := by
-  rw [find?_eq_some]
+  rw [find?_eq_some_iff_append]
   simp only [Bool.not_eq_eq_eq_not, Bool.not_true, exists_and_right, mem_range'_1,
     and_congr_right_iff]
   simp only [range'_eq_append_iff, eq_comm (a := i :: _), range'_eq_cons_iff]
@@ -154,7 +154,7 @@ theorem erase_range' :
 /-! ### range -/
 
 theorem reverse_range' : ∀ s n : Nat, reverse (range' s n) = map (s + n - 1 - ·) (range n)
-  | s, 0 => rfl
+  | _, 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]
@@ -169,7 +169,7 @@ 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']
+  simp +decide 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 _)
@@ -177,10 +177,10 @@ theorem pairwise_le_range (n : Nat) : Pairwise (· ≤ ·) (range n) :=
 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]
+  · simp +contextual [getElem_take, Nat.lt_min]
 
 theorem nodup_range (n : Nat) : Nodup (range n) := by
-  simp (config := {decide := true}) only [range_eq_range', nodup_range']
+  simp +decide only [range_eq_range', nodup_range']
 
 @[simp] theorem find?_range_eq_some {n : Nat} {i : Nat} {p : Nat → Bool} :
     (range n).find? p = some i ↔ p i ∧ i ∈ range n ∧ ∀ j, j < i → !p j := by
@@ -282,7 +282,7 @@ theorem find?_iota_eq_none {n : Nat} {p : Nat → Bool} :
 
 @[simp] theorem find?_iota_eq_some {n : Nat} {i : Nat} {p : Nat → Bool} :
     (iota n).find? p = some i ↔ p i ∧ i ∈ iota n ∧ ∀ j, i < j → j ≤ n → !p j := by
-  rw [find?_eq_some]
+  rw [find?_eq_some_iff_append]
   simp only [iota_eq_reverse_range', reverse_eq_append_iff, reverse_cons, append_assoc, cons_append,
     nil_append, Bool.not_eq_eq_eq_not, Bool.not_true, exists_and_right, mem_reverse, mem_range'_1,
     and_congr_right_iff]
@@ -430,7 +430,10 @@ theorem enumFrom_eq_append_iff {l : List α} {n : Nat} :
 /-! ### enum -/
 
 @[simp]
-theorem enum_eq_nil {l : List α} : List.enum l = [] ↔ l = [] := enumFrom_eq_nil
+theorem enum_eq_nil_iff {l : List α} : List.enum l = [] ↔ l = [] := enumFrom_eq_nil
+
+@[deprecated enum_eq_nil_iff (since := "2024-11-04")]
+theorem enum_eq_nil {l : List α} : List.enum l = [] ↔ l = [] := enum_eq_nil_iff
 
 @[simp] theorem enum_singleton (x : α) : enum [x] = [(0, x)] := rfl
 
@@ -500,4 +503,13 @@ theorem enum_eq_zip_range (l : List α) : l.enum = (range l.length).zip l :=
 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]
 
+theorem enum_eq_cons_iff {l : List α} :
+    l.enum = x :: l' ↔ ∃ a as, l = a :: as ∧ x = (0, a) ∧ l' = enumFrom 1 as := by
+  rw [enum, enumFrom_eq_cons_iff]
+
+theorem enum_eq_append_iff {l : List α} :
+    l.enum = l₁ ++ l₂ ↔
+      ∃ l₁' l₂', l = l₁' ++ l₂' ∧ l₁ = l₁'.enum ∧ l₂ = l₂'.enumFrom l₁'.length := by
+  simp [enum, enumFrom_eq_append_iff]
+
 end List

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

@@ -42,7 +42,7 @@ theorem getElem_take' (L : List α) {i j : Nat} (hi : i < L.length) (hj : i < j)
 
 /-- 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} :
+@[simp] 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]
@@ -52,7 +52,7 @@ 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]
+  simp
 
 /-- 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. -/
@@ -187,6 +187,9 @@ theorem take_add (l : List α) (m n : Nat) : l.take (m + n) = l.take m ++ (l.dro
   · apply length_take_le
   · apply Nat.le_add_right
 
+theorem take_one {l : List α} : l.take 1 = l.head?.toList := by
+  induction l <;> simp
+
 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]
@@ -282,14 +285,14 @@ theorem mem_drop_iff_getElem {l : List α} {a : α} :
   · rintro ⟨i, hm, rfl⟩
     refine ⟨i, by simp; omega, by rw [getElem_drop]⟩
 
-theorem head?_drop (l : List α) (n : Nat) :
+@[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 ≠ []) :
+@[simp] 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 [getElem?_eq_getElem, h, w, head_eq_iff_head?_eq_some] using head?_drop l n
+  simp [getElem?_eq_getElem, h, w, head_eq_iff_head?_eq_some]
 
 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]
@@ -300,7 +303,7 @@ theorem getLast?_drop {l : List α} : (l.drop n).getLast? = if l.length ≤ n th
     congr
     omega
 
-theorem getLast_drop {l : List α} (h : l.drop n ≠ []) :
+@[simp] 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] at h
   apply Option.some_inj.1
@@ -449,6 +452,26 @@ theorem reverse_drop {l : List α} {n : Nat} :
     rw [w, take_zero, drop_of_length_le, reverse_nil]
     omega
 
+theorem take_add_one {l : List α} {n : Nat} :
+    l.take (n + 1) = l.take n ++ l[n]?.toList := by
+  simp [take_add, take_one]
+
+theorem drop_eq_getElem?_toList_append {l : List α} {n : Nat} :
+    l.drop n = l[n]?.toList ++ l.drop (n + 1) := by
+  induction l generalizing n with
+  | nil => simp
+  | cons hd tl ih =>
+    cases n
+    · simp
+    · simp only [drop_succ_cons, getElem?_cons_succ]
+      rw [ih]
+
+theorem drop_sub_one {l : List α} {n : Nat} (h : 0 < n) :
+    l.drop (n - 1) = l[n - 1]?.toList ++ l.drop n := by
+  rw [drop_eq_getElem?_toList_append]
+  congr
+  omega
+
 /-! ### findIdx -/
 
 theorem false_of_mem_take_findIdx {xs : List α} {p : α → Bool} (h : x ∈ xs.take (xs.findIdx p)) :

src/Init/Data/List/OfFn.lean

@@ -0,0 +1,80 @@
+/-
+Copyright (c) 2024 Lean FRO. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Mario Carneiro, Kim Morrison
+-/
+prelude
+import Init.Data.List.Basic
+import Init.Data.Fin.Fold
+
+/-!
+# Theorems about `List.ofFn`
+-/
+
+namespace List
+
+/--
+`ofFn f` with `f : fin n → α` returns the list whose ith element is `f i`
+```
+ofFn f = [f 0, f 1, ... , f (n - 1)]
+```
+-/
+def ofFn {n} (f : Fin n → α) : List α := Fin.foldr n (f · :: ·) []
+
+@[simp]
+theorem length_ofFn (f : Fin n → α) : (ofFn f).length = n := by
+  simp only [ofFn]
+  induction n with
+  | zero => simp
+  | succ n ih => simp [Fin.foldr_succ, ih]
+
+@[simp]
+protected theorem getElem_ofFn (f : Fin n → α) (i : Nat) (h : i < (ofFn f).length) :
+    (ofFn f)[i] = f ⟨i, by simp_all⟩ := by
+  simp only [ofFn]
+  induction n generalizing i with
+  | zero => simp at h
+  | succ n ih =>
+    match i with
+    | 0 => simp [Fin.foldr_succ]
+    | i+1 =>
+      simp only [Fin.foldr_succ]
+      apply ih
+      simp_all
+
+@[simp]
+protected theorem getElem?_ofFn (f : Fin n → α) (i) : (ofFn f)[i]? = if h : i < n then some (f ⟨i, h⟩) else none :=
+  if h : i < (ofFn f).length
+  then by
+    rw [getElem?_eq_getElem h, List.getElem_ofFn]
+    · simp only [length_ofFn] at h; simp [h]
+  else by
+    rw [dif_neg] <;>
+    simpa using h
+
+/-- `ofFn` on an empty domain is the empty list. -/
+@[simp]
+theorem ofFn_zero (f : Fin 0 → α) : ofFn f = [] :=
+  ext_get (by simp) (fun i hi₁ hi₂ => by contradiction)
+
+@[simp]
+theorem ofFn_succ {n} (f : Fin (n + 1) → α) : ofFn f = f 0 :: ofFn fun i => f i.succ :=
+  ext_get (by simp) (fun i hi₁ hi₂ => by
+    cases i
+    · simp
+    · simp)
+
+@[simp]
+theorem ofFn_eq_nil_iff {f : Fin n → α} : ofFn f = [] ↔ n = 0 := by
+  cases n <;> simp only [ofFn_zero, ofFn_succ, eq_self_iff_true, Nat.succ_ne_zero, reduceCtorEq]
+
+theorem head_ofFn {n} (f : Fin n → α) (h : ofFn f ≠ []) :
+    (ofFn f).head h = f ⟨0, Nat.pos_of_ne_zero (mt ofFn_eq_nil_iff.2 h)⟩ := by
+  rw [← getElem_zero (length_ofFn _ ▸ Nat.pos_of_ne_zero (mt ofFn_eq_nil_iff.2 h)),
+    List.getElem_ofFn]
+
+theorem getLast_ofFn {n} (f : Fin n → α) (h : ofFn f ≠ []) :
+    (ofFn f).getLast h = f ⟨n - 1, Nat.sub_one_lt (mt ofFn_eq_nil_iff.2 h)⟩ := by
+  simp [getLast_eq_getElem, length_ofFn, List.getElem_ofFn]
+
+end List

src/Init/Data/List/Pairwise.lean

@@ -76,11 +76,11 @@ theorem pairwise_of_forall {l : List α} (H : ∀ x y, R x y) : Pairwise R l :=
 
 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 })
+  Pairwise.iff_of_mem <| by simp +contextual
 
 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 })
+  Pairwise.iff_of_mem <| by simp +contextual
 
 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
@@ -160,21 +160,25 @@ theorem pairwise_middle {R : α → α → Prop} (s : ∀ {x y}, R x y → R y x
   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) ↔
+theorem pairwise_flatten {L : List (List α)} :
+    Pairwise R (flatten 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,
+    simp only [flatten, pairwise_append, IH, mem_flatten, 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) ↔
+@[deprecated pairwise_flatten (since := "2024-10-14")] abbrev pairwise_join := @pairwise_flatten
+
+theorem pairwise_flatMap {R : β → β → Prop} {l : List α} {f : α → List β} :
+    List.Pairwise R (l.flatMap 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]
+  simp [List.flatMap, pairwise_flatten, pairwise_map]
+
+@[deprecated pairwise_flatMap (since := "2024-10-14")] abbrev pairwise_bind := @pairwise_flatMap
 
 theorem pairwise_reverse {l : List α} :
     l.reverse.Pairwise R ↔ l.Pairwise (fun a b => R b a) := by

src/Init/Data/List/Perm.lean

@@ -98,8 +98,8 @@ theorem Perm.append_cons (a : α) {h₁ h₂ t₁ t₂ : List α} (p₁ : h₁ ~
   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
+  | [], _ => by simp
+  | _ :: _, _ => (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
@@ -114,6 +114,14 @@ theorem Perm.length_eq {l₁ l₂ : List α} (p : l₁ ~ l₂) : length l₁ = l
   | swap => rfl
   | trans _ _ ih₁ ih₂ => simp only [ih₁, ih₂]
 
+theorem Perm.contains_eq [BEq α] {l₁ l₂ : List α} (h : l₁ ~ l₂) {a : α} :
+    l₁.contains a = l₂.contains a := by
+  induction h with
+  | nil => rfl
+  | cons => simp_all
+  | swap => simp only [contains_cons, ← Bool.or_assoc, Bool.or_comm]
+  | trans => simp_all
+
 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
@@ -248,6 +256,10 @@ theorem countP_eq_countP_filter_add (l : List α) (p q : α → Bool) :
 theorem Perm.count_eq [DecidableEq α] {l₁ l₂ : List α} (p : l₁ ~ l₂) (a) :
     count a l₁ = count a l₂ := p.countP_eq _
 
+/-
+This theorem is a variant of `Perm.foldl_eq` defined in Mathlib which uses typeclasses rather
+than the explicit `comm` argument.
+-/
 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
@@ -264,6 +276,28 @@ theorem Perm.foldl_eq' {f : β → α → β} {l₁ l₂ : List α} (p : l₁ ~
     refine (IH₁ comm init).trans (IH₂ ?_ _)
     intros; apply comm <;> apply p₁.symm.subset <;> assumption
 
+/-
+This theorem is a variant of `Perm.foldr_eq` defined in Mathlib which uses typeclasses rather
+than the explicit `comm` argument.
+-/
+theorem Perm.foldr_eq' {f : α → β → β} {l₁ l₂ : List α} (p : l₁ ~ l₂)
+    (comm : ∀ x ∈ l₁, ∀ y ∈ l₁, ∀ (z), f y (f x z) = f x (f y z))
+    (init) : foldr f init l₁ = foldr f init l₂ := by
+  induction p using recOnSwap' generalizing init with
+  | nil => simp
+  | cons x _p IH =>
+    simp only [foldr]
+    congr 1
+    apply IH; intros; apply comm <;> exact .tail _ ‹_›
+  | swap' x y _p IH =>
+    simp only [foldr]
+    rw [comm x (.tail _ <| .head _) y (.head _)]
+    congr 2
+    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))) :
@@ -435,15 +469,19 @@ theorem Perm.nodup {l l' : List α} (hl : l ~ l') (hR : l.Nodup) : l'.Nodup := h
 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
+theorem Perm.flatten {l₁ l₂ : List (List α)} (h : l₁ ~ l₂) : l₁.flatten ~ l₂.flatten := 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 ..
+  | cons _ _ ih => simp only [flatten_cons, perm_append_left_iff, ih]
+  | swap => simp only [flatten_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
+@[deprecated Perm.flatten (since := "2024-10-14")] abbrev Perm.join := @Perm.flatten
+
+theorem Perm.flatMap_right {l₁ l₂ : List α} (f : α → List β) (p : l₁ ~ l₂) : l₁.flatMap f ~ l₂.flatMap f :=
+  (p.map _).flatten
+
+@[deprecated Perm.flatMap_right (since := "2024-10-16")] abbrev Perm.bind_right := @Perm.flatMap_right
 
 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

src/Init/Data/List/Range.lean

@@ -20,7 +20,6 @@ open Nat
 
 /-! ## Ranges and enumeration -/
 
-
 /-! ### range' -/
 
 theorem range'_succ (s n step) : range' s (n + 1) step = s :: range' (s + step) n step := by
@@ -92,7 +91,7 @@ theorem map_add_range' (a) : ∀ s n step, map (a + ·) (range' s n step) = rang
 
 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
+  | _, 0, _, _ => 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
@@ -131,7 +130,7 @@ theorem range'_eq_cons_iff : range' s n = a :: xs ↔ s = a ∧ 0 < n ∧ xs = r
 /-! ### range -/
 
 theorem range_loop_range' : ∀ s n : Nat, range.loop s (range' s n) = range' 0 (n + s)
-  | 0, n => rfl
+  | 0, _ => 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 :=
@@ -214,9 +213,9 @@ theorem enumFrom_eq_nil {n : Nat} {l : List α} : List.enumFrom n l = [] ↔ l =
 @[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
+  | _, [], _ => rfl
+  | _, _ :: _, 0 => by simp
+  | n, _ :: 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
 

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

@@ -102,7 +102,7 @@ def mergeSortTR (l : List α) (le : α → α → Bool := by exact fun a b => a
 where run : {n : Nat} → { l : List α // l.length = n } → List α
   | 0, ⟨[], _⟩ => []
   | 1, ⟨[a], _⟩ => [a]
-  | n+2, xs =>
+  | _+2, xs =>
     let (l, r) := splitInTwo xs
     mergeTR (run l) (run r) le
 
@@ -136,13 +136,13 @@ where
   run : {n : Nat} → { l : List α // l.length = n } → List α
   | 0, ⟨[], _⟩ => []
   | 1, ⟨[a], _⟩ => [a]
-  | n+2, xs =>
+  | _+2, xs =>
     let (l, r) := splitRevInTwo xs
     mergeTR (run' l) (run r) le
   run' : {n : Nat} → { l : List α // l.length = n } → List α
   | 0, ⟨[], _⟩ => []
   | 1, ⟨[a], _⟩ => [a]
-  | n+2, xs =>
+  | _+2, xs =>
     let (l, r) := splitRevInTwo' xs
     mergeTR (run' r) (run l) le
 

src/Init/Data/List/Sublist.lean

@@ -116,7 +116,7 @@ fun s => Subset.trans s <| subset_append_right _ _
 theorem replicate_subset {n : Nat} {a : α} {l : List α} : replicate n a ⊆ l ↔ n = 0 ∨ a ∈ l := by
   induction n with
   | zero => simp
-  | succ n ih => simp (config := {contextual := true}) [replicate_succ, ih, cons_subset]
+  | succ n ih => simp +contextual [replicate_succ, ih, cons_subset]
 
 theorem subset_replicate {n : Nat} {a : α} {l : List α} (h : n ≠ 0) : l ⊆ replicate n a ↔ ∀ x ∈ l, x = a := by
   induction l with
@@ -483,30 +483,30 @@ theorem sublist_replicate_iff : l <+ replicate m a ↔ ∃ n, n ≤ m ∧ l = re
       rw [w]
       exact (replicate_sublist_replicate a).2 le
 
-theorem sublist_join_of_mem {L : List (List α)} {l} (h : l ∈ L) : l <+ L.join := by
+theorem sublist_flatten_of_mem {L : List (List α)} {l} (h : l ∈ L) : l <+ L.flatten := by
   induction L with
   | nil => cases h
   | cons l' L ih =>
     rcases mem_cons.1 h with (rfl | h)
     · simp [h]
-    · simp [ih h, join_cons, sublist_append_of_sublist_right]
+    · simp [ih h, flatten_cons, sublist_append_of_sublist_right]
 
-theorem sublist_join_iff {L : List (List α)} {l} :
-    l <+ L.join ↔
-      ∃ L' : List (List α), l = L'.join ∧ ∀ i (_ : i < L'.length), L'[i] <+ L[i]?.getD [] := by
+theorem sublist_flatten_iff {L : List (List α)} {l} :
+    l <+ L.flatten ↔
+      ∃ L' : List (List α), l = L'.flatten ∧ ∀ i (_ : i < L'.length), L'[i] <+ L[i]?.getD [] := by
   induction L generalizing l with
   | nil =>
     constructor
     · intro w
-      simp only [join_nil, sublist_nil] at w
+      simp only [flatten_nil, sublist_nil] at w
       subst w
       exact ⟨[], by simp, fun i x => by cases x⟩
     · rintro ⟨L', rfl, h⟩
-      simp only [join_nil, sublist_nil, join_eq_nil_iff]
+      simp only [flatten_nil, sublist_nil, flatten_eq_nil_iff]
       simp only [getElem?_nil, Option.getD_none, sublist_nil] at h
       exact (forall_getElem (p := (· = []))).1 h
   | cons l' L ih =>
-    simp only [join_cons, sublist_append_iff, ih]
+    simp only [flatten_cons, sublist_append_iff, ih]
     constructor
     · rintro ⟨l₁, l₂, rfl, s, L', rfl, h⟩
       refine ⟨l₁ :: L', by simp, ?_⟩
@@ -517,21 +517,21 @@ theorem sublist_join_iff {L : List (List α)} {l} :
       | nil =>
         exact ⟨[], [], by simp, by simp, [], by simp, fun i x => by cases x⟩
       | cons l₁ L' =>
-        exact ⟨l₁, L'.join, by simp, by simpa using h 0 (by simp), L', rfl,
+        exact ⟨l₁, L'.flatten, by simp, by simpa using h 0 (by simp), L', rfl,
           fun i lt => by simpa using h (i+1) (Nat.add_lt_add_right lt 1)⟩
 
-theorem join_sublist_iff {L : List (List α)} {l} :
-    L.join <+ l ↔
-      ∃ L' : List (List α), l = L'.join ∧ ∀ i (_ : i < L.length), L[i] <+ L'[i]?.getD [] := by
+theorem flatten_sublist_iff {L : List (List α)} {l} :
+    L.flatten <+ l ↔
+      ∃ L' : List (List α), l = L'.flatten ∧ ∀ i (_ : i < L.length), L[i] <+ L'[i]?.getD [] := by
   induction L generalizing l with
   | nil =>
     constructor
     · intro _
       exact ⟨[l], by simp, fun i x => by cases x⟩
     · rintro ⟨L', rfl, _⟩
-      simp only [join_nil, nil_sublist]
+      simp only [flatten_nil, nil_sublist]
   | cons l' L ih =>
-    simp only [join_cons, append_sublist_iff, ih]
+    simp only [flatten_cons, append_sublist_iff, ih]
     constructor
     · rintro ⟨l₁, l₂, rfl, s, L', rfl, h⟩
       refine ⟨l₁ :: L', by simp, ?_⟩
@@ -543,7 +543,7 @@ theorem join_sublist_iff {L : List (List α)} {l} :
         exact ⟨[], [], by simp, by simpa using h 0 (by simp), [], by simp,
           fun i x => by simpa using h (i+1) (Nat.add_lt_add_right x 1)⟩
       | cons l₁ L' =>
-        exact ⟨l₁, L'.join, by simp, by simpa using h 0 (by simp), L', rfl,
+        exact ⟨l₁, L'.flatten, by simp, by simpa using h 0 (by simp), L', rfl,
           fun i lt => by simpa using h (i+1) (Nat.add_lt_add_right lt 1)⟩
 
 @[simp] theorem isSublist_iff_sublist [BEq α] [LawfulBEq α] {l₁ l₂ : List α} :
@@ -725,16 +725,25 @@ theorem infix_iff_suffix_prefix {l₁ l₂ : List α} : l₁ <:+: l₂ ↔ ∃ t
 theorem IsInfix.eq_of_length (h : l₁ <:+: l₂) : l₁.length = l₂.length → l₁ = l₂ :=
   h.sublist.eq_of_length
 
+theorem IsInfix.eq_of_length_le (h : l₁ <:+: l₂) : l₂.length ≤ l₁.length → l₁ = l₂ :=
+  h.sublist.eq_of_length_le
+
 theorem IsPrefix.eq_of_length (h : l₁ <+: l₂) : l₁.length = l₂.length → l₁ = l₂ :=
   h.sublist.eq_of_length
 
+theorem IsPrefix.eq_of_length_le (h : l₁ <+: l₂) : l₂.length ≤ l₁.length → l₁ = l₂ :=
+  h.sublist.eq_of_length_le
+
 theorem IsSuffix.eq_of_length (h : l₁ <:+ l₂) : l₁.length = l₂.length → l₁ = l₂ :=
   h.sublist.eq_of_length
 
+theorem IsSuffix.eq_of_length_le (h : l₁ <:+ l₂) : l₂.length ≤ l₁.length → l₁ = l₂ :=
+  h.sublist.eq_of_length_le
+
 theorem prefix_of_prefix_length_le :
     ∀ {l₁ l₂ l₃ : List α}, l₁ <+: l₃ → l₂ <+: l₃ → length l₁ ≤ length l₂ → l₁ <+: l₂
-  | [], l₂, _, _, _, _ => nil_prefix
-  | a :: l₁, b :: l₂, _, ⟨r₁, rfl⟩, ⟨r₂, e⟩, ll => by
+  | [], _, _, _, _, _ => nil_prefix
+  | _ :: _, b :: _, _, ⟨_, rfl⟩, ⟨_, e⟩, ll => by
     injection e with _ e'; subst b
     rcases prefix_of_prefix_length_le ⟨_, rfl⟩ ⟨_, e'⟩ (le_of_succ_le_succ ll) with ⟨r₃, rfl⟩
     exact ⟨r₃, rfl⟩
@@ -826,9 +835,27 @@ theorem isPrefix_iff : l₁ <+: l₂ ↔ ∀ i (h : i < l₁.length), l₂[i]? =
       simpa using ⟨0, by simp⟩
     | cons b l₂ =>
       simp only [cons_append, cons_prefix_cons, ih]
-      rw (config := {occs := .pos [2]}) [← Nat.and_forall_add_one]
+      rw (occs := .pos [2]) [← Nat.and_forall_add_one]
       simp [Nat.succ_lt_succ_iff, eq_comm]
 
+theorem isPrefix_iff_getElem {l₁ l₂ : List α} :
+    l₁ <+: l₂ ↔ ∃ (h : l₁.length ≤ l₂.length), ∀ x (hx : x < l₁.length),
+      l₁[x] = l₂[x]'(Nat.lt_of_lt_of_le hx h) where
+  mp h := ⟨h.length_le, fun _ _ ↦ h.getElem _⟩
+  mpr h := by
+    obtain ⟨hl, h⟩ := h
+    induction l₂ generalizing l₁ with
+    | nil =>
+      simpa using hl
+    | cons _ _ tail_ih =>
+      cases l₁ with
+      | nil =>
+        exact nil_prefix
+      | cons _ _ =>
+        simp only [length_cons, Nat.add_le_add_iff_right, Fin.getElem_fin] at hl h
+        simp only [cons_prefix_cons]
+        exact ⟨h 0 (zero_lt_succ _), tail_ih hl fun a ha ↦ h a.succ (succ_lt_succ ha)⟩
+
 -- See `Init.Data.List.Nat.Sublist` for `isSuffix_iff` and `ifInfix_iff`.
 
 theorem isPrefix_filterMap_iff {β} {f : α → Option β} {l₁ : List α} {l₂ : List β} :
@@ -911,14 +938,14 @@ theorem isInfix_replicate_iff {n} {a : α} {l : List α} :
     · simpa using Nat.sub_add_cancel h
     · simpa using w
 
-theorem infix_of_mem_join : ∀ {L : List (List α)}, l ∈ L → l <:+: join L
+theorem infix_of_mem_flatten : ∀ {L : List (List α)}, l ∈ L → l <:+: flatten L
   | l' :: _, h =>
     match h with
     | List.Mem.head .. => infix_append [] _ _
     | List.Mem.tail _ hlMemL =>
-      IsInfix.trans (infix_of_mem_join hlMemL) <| (suffix_append _ _).isInfix
+      IsInfix.trans (infix_of_mem_flatten hlMemL) <| (suffix_append _ _).isInfix
 
-theorem prefix_append_right_inj (l) : l ++ l₁ <+: l ++ l₂ ↔ l₁ <+: l₂ :=
+@[simp] theorem prefix_append_right_inj (l) : l ++ l₁ <+: l ++ l₂ ↔ l₁ <+: l₂ :=
   exists_congr fun r => by rw [append_assoc, append_right_inj]
 
 theorem prefix_cons_inj (a) : a :: l₁ <+: a :: l₂ ↔ l₁ <+: l₂ :=
@@ -949,7 +976,7 @@ theorem mem_of_mem_drop {n} {l : List α} (h : a ∈ l.drop n) : a ∈ l :=
   drop_subset _ _ h
 
 theorem drop_suffix_drop_left (l : List α) {m n : Nat} (h : m ≤ n) : drop n l <:+ drop m l := by
-  rw [← Nat.sub_add_cancel h, ← drop_drop]
+  rw [← Nat.sub_add_cancel h, Nat.add_comm, ← drop_drop]
   apply drop_suffix
 
 -- See `Init.Data.List.Nat.TakeDrop` for `take_prefix_take_left`.
@@ -1060,4 +1087,11 @@ theorem prefix_iff_eq_take : l₁ <+: l₂ ↔ l₁ = take (length l₁) l₂ :=
 
 -- See `Init.Data.List.Nat.Sublist` for `suffix_iff_eq_append`, `prefix_take_iff`, and `suffix_iff_eq_drop`.
 
+/-! ### Deprecations -/
+
+@[deprecated sublist_flatten_of_mem (since := "2024-10-14")] abbrev sublist_join_of_mem := @sublist_flatten_of_mem
+@[deprecated sublist_flatten_iff (since := "2024-10-14")] abbrev sublist_join_iff := @sublist_flatten_iff
+@[deprecated flatten_sublist_iff (since := "2024-10-14")] abbrev flatten_join_iff := @flatten_sublist_iff
+@[deprecated infix_of_mem_flatten (since := "2024-10-14")] abbrev infix_of_mem_join := @infix_of_mem_flatten
+
 end List

src/Init/Data/List/TakeDrop.lean

@@ -97,14 +97,14 @@ theorem get?_take {l : List α} {n m : Nat} (h : m < n) : (l.take n).get? m = l.
 
 theorem getElem?_take_of_succ {l : List α} {n : Nat} : (l.take (n + 1))[n]? = l[n]? := by simp
 
-@[simp] theorem drop_drop (n : Nat) : ∀ (m) (l : List α), drop n (drop m l) = drop (n + m) l
+@[simp] theorem drop_drop (n : Nat) : ∀ (m) (l : List α), drop n (drop m l) = drop (m + n) 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
+      _ = drop (m + n) l := drop_drop n m l
+      _ = drop ((m + 1) + n) (a :: l) := by rw [Nat.add_right_comm]; rfl
 
 theorem take_drop : ∀ (m n : Nat) (l : List α), take n (drop m l) = drop m (take (m + n) l)
   | 0, _, _ => by simp
@@ -112,7 +112,7 @@ theorem take_drop : ∀ (m n : Nat) (l : List α), take n (drop m l) = drop m (t
   | _+1, _, _ :: _ => by simpa [Nat.succ_add, take_succ_cons, drop_succ_cons] using take_drop ..
 
 @[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
+theorem drop_add (m n) (l : List α) : drop (m + n) l = drop n (drop m l) := by
   simp [drop_drop]
 
 @[simp]
@@ -126,7 +126,7 @@ theorem tail_drop (l : List α) (n : Nat) : (l.drop n).tail = l.drop (n + 1) :=
 
 @[simp]
 theorem drop_tail (l : List α) (n : Nat) : l.tail.drop n = l.drop (n + 1) := by
-  rw [← drop_drop, drop_one]
+  rw [Nat.add_comm, ← drop_drop, drop_one]
 
 @[simp]
 theorem drop_eq_nil_iff {l : List α} {k : Nat} : l.drop k = [] ↔ l.length ≤ k := by
@@ -190,7 +190,7 @@ theorem set_drop {l : List α} {n m : Nat} {a : α} :
 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]
+    rw [concat_eq_append, append_assoc, singleton_append, getElem_cons_drop_succ_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

src/Init/Data/List/ToArray.lean

@@ -0,0 +1,23 @@
+/-
+Copyright (c) 2024 Lean FRO. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+Authors: Henrik Böving
+-/
+prelude
+import Init.Data.List.Basic
+
+/--
+Auxiliary definition for `List.toArray`.
+`List.toArrayAux as r = r ++ as.toArray`
+-/
+@[inline_if_reduce]
+def List.toArrayAux : List α → Array α → Array α
+  | nil,       r => r
+  | cons a as, r => toArrayAux as (r.push a)
+
+/-- Convert a `List α` into an `Array α`. This is O(n) in the length of the list.  -/
+-- This function is exported to C, where it is called by `Array.mk`
+-- (the constructor) to implement this functionality.
+@[inline, match_pattern, pp_nodot, export lean_list_to_array]
+def List.toArrayImpl (as : List α) : Array α :=
+  as.toArrayAux (Array.mkEmpty as.length)

src/Init/Data/List/Zip.lean

@@ -5,6 +5,7 @@ Authors: Parikshit Khanna, Jeremy Avigad, Leonardo de Moura, Floris van Doorn, M
 -/
 prelude
 import Init.Data.List.TakeDrop
+import Init.Data.Function
 
 /-!
 # Lemmas about `List.zip`, `List.zipWith`, `List.zipWithAll`, and `List.unzip`.
@@ -238,6 +239,14 @@ theorem zipWith_eq_append_iff {f : α → β → γ} {l₁ : List α} {l₂ : Li
   | zero => rfl
   | succ n ih => simp [replicate_succ, ih]
 
+theorem map_uncurry_zip_eq_zipWith (f : α → β → γ) (l : List α) (l' : List β) :
+    map (Function.uncurry f) (l.zip l') = zipWith f l l' := by
+  rw [zip]
+  induction l generalizing l' with
+  | nil => simp
+  | cons hl tl ih =>
+    cases l' <;> simp [ih]
+
 /-! ### zip -/
 
 theorem zip_eq_zipWith : ∀ (l₁ : List α) (l₂ : List β), zip l₁ l₂ = zipWith Prod.mk l₁ l₂
@@ -247,9 +256,9 @@ theorem zip_eq_zipWith : ∀ (l₁ : List α) (l₂ : List β), zip l₁ l₂ =
 
 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
+  | [], _ => rfl
+  | _, [] => by simp only [map, zip_nil_right]
+  | _ :: _, _ :: _ => 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) :
@@ -287,12 +296,12 @@ theorem of_mem_zip {a b} : ∀ {l₁ : List α} {l₂ : List β}, (a, b) ∈ zip
 
 theorem map_fst_zip :
     ∀ (l₁ : List α) (l₂ : List β), l₁.length ≤ l₂.length → map Prod.fst (zip l₁ l₂) = l₁
-  | [], bs, _ => rfl
+  | [], _, _ => 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
+  | _ :: _, [], 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
@@ -430,9 +439,9 @@ theorem zip_unzip : ∀ l : List (α × β), zip (unzip l).1 (unzip l).2 = 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
+  | [], _, _ => rfl
+  | _, [], h => by rw [eq_nil_of_length_eq_zero (Nat.eq_zero_of_le_zero h)]; rfl
+  | _ :: _, _ :: _, h => by
     simp only [zip_cons_cons, unzip_cons, unzip_zip_left (le_of_succ_le_succ h)]
 
 theorem unzip_zip_right :

src/Init/Data/Nat/Basic.lean

@@ -131,7 +131,7 @@ theorem or_exists_add_one : p 0 ∨ (Exists fun n => p (n + 1)) ↔ Exists p :=
 @[simp] theorem blt_eq : (Nat.blt x y = true) = (x < y) := propext <| Iff.intro Nat.le_of_ble_eq_true Nat.ble_eq_true_of_le
 
 instance : LawfulBEq Nat where
-  eq_of_beq h := Nat.eq_of_beq_eq_true h
+  eq_of_beq h := by simpa using h
   rfl := by simp [BEq.beq]
 
 theorem beq_eq_true_eq (a b : Nat) : ((a == b) = true) = (a = b) := by simp
@@ -248,7 +248,7 @@ protected theorem add_mul (n m k : Nat) : (n + m) * k = n * k + m * k :=
   Nat.right_distrib n m k
 
 protected theorem mul_assoc : ∀ (n m k : Nat), (n * m) * k = n * (m * k)
-  | n, m, 0      => rfl
+  | _, _, 0      => rfl
   | n, m, succ k => by simp [mul_succ, Nat.mul_assoc n m k, Nat.left_distrib]
 instance : Std.Associative (α := Nat) (· * ·) := ⟨Nat.mul_assoc⟩
 
@@ -490,10 +490,10 @@ protected theorem le_antisymm_iff {a b : Nat} : a = b ↔ a ≤ b ∧ b ≤ a :=
             (fun ⟨hle, hge⟩ => Nat.le_antisymm hle hge)
 protected theorem eq_iff_le_and_ge : ∀{a b : Nat}, a = b ↔ a ≤ b ∧ b ≤ a := @Nat.le_antisymm_iff
 
-instance : Antisymm ( . ≤ . : Nat → Nat → Prop) where
+instance : Std.Antisymm ( . ≤ . : Nat → Nat → Prop) where
   antisymm h₁ h₂ := Nat.le_antisymm h₁ h₂
 
-instance : Antisymm (¬ . < . : Nat → Nat → Prop) where
+instance : Std.Antisymm (¬ . < . : Nat → Nat → Prop) where
   antisymm h₁ h₂ := Nat.le_antisymm (Nat.ge_of_not_lt h₂) (Nat.ge_of_not_lt h₁)
 
 protected theorem add_le_add_left {n m : Nat} (h : n ≤ m) (k : Nat) : k + n ≤ k + m :=
@@ -634,6 +634,8 @@ theorem lt_succ_of_lt (h : a < b) : a < succ b := le_succ_of_le h
 
 theorem lt_add_one_of_lt (h : a < b) : a < b + 1 := le_succ_of_le h
 
+@[simp] theorem lt_one_iff : n < 1 ↔ n = 0 := Nat.lt_succ_iff.trans <| by rw [le_zero_eq]
+
 theorem succ_pred_eq_of_ne_zero : ∀ {n}, n ≠ 0 → succ (pred n) = n
   | _+1, _ => rfl
 
@@ -794,6 +796,8 @@ theorem pos_pow_of_pos {n : Nat} (m : Nat) (h : 0 < n) : 0 < n^m :=
   | zero => cases h
   | succ n => simp [Nat.pow_succ]
 
+protected theorem two_pow_pos (w : Nat) : 0 < 2^w := Nat.pos_pow_of_pos _ (by decide)
+
 instance {n m : Nat} [NeZero n] : NeZero (n^m) :=
   ⟨Nat.ne_zero_iff_zero_lt.mpr (Nat.pos_pow_of_pos m (pos_of_neZero _))⟩
 

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

@@ -357,7 +357,7 @@ theorem testBit_two_pow_of_ne {n m : Nat} (hm : n ≠ m) : testBit (2 ^ n) m = f
   | zero => simp
   | succ n =>
     rw [mod_eq_of_lt (a := 1) (Nat.one_lt_two_pow (by omega)), mod_two_eq_one_iff_testBit_zero, testBit_two_pow_sub_one ]
-    simp only [zero_lt_succ, decide_True]
+    simp only [zero_lt_succ, decide_true]
 
 @[simp] theorem mod_two_pos_mod_two_eq_one : x % 2 ^ j % 2 = 1 ↔ (0 < j) ∧ x % 2 = 1 := by
   rw [mod_two_eq_one_iff_testBit_zero, testBit_mod_two_pow]