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Lean 4 fork for HoTT-compatible kernel extensions (Path types, transport, HITs). Maintained against upstream leanprover/lean4.
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Kim Morrison fa4cd6d78c
feat: add theorems relating find? with findIdx? and findFinIdx? (#12204) 
This PR adds theorems showing the consistency between `find?` and the
various index-finding functions. The theorems establish bidirectional
relationships between finding elements and finding their indices.

**Forward direction** (find? in terms of index):
- `find?_eq_map_findFinIdx?_getElem`: `xs.find? p = (xs.findFinIdx?
p).map (xs[·])`
- `find?_eq_bind_findIdx?_getElem?`: `xs.find? p = (xs.findIdx? p).bind
(xs[·]?)`
- `find?_eq_getElem?_findIdx`: `xs.find? p = xs[xs.findIdx p]?`

**Reverse direction** (index in terms of find?):
- `findIdx?_eq_bind_find?_idxOf?`: `xs.findIdx? p = (xs.find? p).bind
(xs.idxOf?)`
- `findFinIdx?_eq_bind_find?_finIdxOf?`: `xs.findFinIdx? p = (xs.find?
p).bind (xs.finIdxOf?)`
- `findIdx_eq_getD_bind_find?_idxOf?`: `xs.findIdx p = ((xs.find?
p).bind (xs.idxOf?)).getD xs.length`

All theorems are provided for `List`, `Array`, and `Vector` (where
applicable).

Requested at
https://leanprover.zulipchat.com/#narrow/channel/113488-general/topic/show.20that.20Array.2Efind.3F.20and.20Array.2EfindFinIdx.3F.20consistent/near/567340199

🤖 Prepared with Claude Code

Co-authored-by: Claude <noreply@anthropic.com>
2026-01-28 04:55:29 +00:00
.claude doc: document release notes process and add guard check (#12158) 2026-01-26 07:16:01 +00:00
.github fix: create PR releases even when test suite fails (#12202) 2026-01-28 03:13:48 +00:00
doc doc: clarify release notes title format requirements (#12182) 2026-01-27 08:08:47 +00:00
images
releases_drafts chore: add release draft for the module system (#11359) 2025-11-26 15:01:07 +00:00
script doc: document release notes process and add guard check (#12158) 2026-01-26 07:16:01 +00:00
src feat: add theorems relating find? with findIdx? and findFinIdx? (#12204) 2026-01-28 04:55:29 +00:00
stage0 chore: update stage0 2026-01-27 20:33:17 +00:00
tests feat: another grind_pattern for getElem?_pos (#11963) 2026-01-28 03:45:54 +00:00
.gitattributes doc: grove: update and add String data (#11551) 2025-12-08 16:49:37 +00:00
.gitignore chore: add .vscode/settings.json to .gitignore (#10795) 2025-10-16 07:08:41 +00:00
.gitpod.Dockerfile chore: add gitpod configuration (#6382) 2024-12-15 21:38:13 +00:00
.gitpod.yml chore: add gitpod configuration (#6382) 2024-12-15 21:38:13 +00:00
.ignore chore: ignore stage0/ (for rg etc.) 2022-03-18 15:28:20 +01:00
CMakeLists.txt fix: cadical dynamic dependencies (#11475) 2025-12-02 13:54:26 +00:00
CMakePresets.json chore: CI: enable leak sanitizer again (#11339) 2025-11-27 18:32:35 +00:00
CODEOWNERS chore: make @hargoniX code owner of the compiler (#10732) 2025-10-10 04:43:38 +00:00
CONTRIBUTING.md doc: triage 2024-07-26 18:24:06 +02:00
flake.lock chore: robustify Nix shell (#8141) 2025-04-28 15:08:32 +00:00
flake.nix chore: use lld if available for building core (#10694) 2025-10-08 16:47:30 +00:00
lean-toolchain doc: VS Code dev setup (#2961) 2023-11-30 08:35:03 +00:00
lean.code-workspace chore: lean.code-workspace: fix terminal cwd (#10802) 2025-10-16 20:19:12 +00:00
LICENSE chore: remove LICENSE header that confused GitHub 2021-11-18 09:42:35 +01:00
LICENSES feat: ship cadical (#4325) 2024-08-23 09:13:27 +00:00
README.md doc: update URLs that are currently pointing to redirects (#10397) 2025-09-17 15:50:07 +00:00
RELEASES.md chore: updates to release_checklist.md (#7817) 2025-04-04 03:45:36 +00:00

README.md

This is the repository for Lean 4.

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Please read our Contribution Guidelines first.

Building from Source

See Building Lean.