leanprover-community/mathlib4

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The math library of Lean 4

Stars: 4.2k
Forks: 1.7k
Open beginner issues: 0
Indexed issues: 284

Dominant language: Lean
License: Apache-2.0
Last GitHub push: Sep 19, 2026
Latest indexed: Sep 18, 2026
Contributing guide: Contributing guide
Code of conduct: Code of conduct
Beginner labels: good first issue help wanted
PR merge metrics: No merged PRs in 30d

Beginner friendly Everything

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284 open issues indexed

Add a Group instance for LieEquiv (automorphisms of a Lie algebra / Lie module) Open

Difficulty 4/5 3-5 days Newbie friendliness 48/100

leanprover-community/mathlib4#43952 · Opened Sep 18, 2026
Improve `Multipliable.inv` / `inv₀` docstrings for `ℂ` (and add `tprod_one_add_ne_zero_of_summable` cross-reference Open

Difficulty 2/5 1-3 hours Newbie friendliness 74/100

leanprover-community/mathlib4#43872 · Opened Sep 16, 2026
Subscript and superscript parsers should produce round-tripping `Syntax` Open

Difficulty 3/5 1-2 days Newbie friendliness 68/100

leanprover-community/mathlib4#43870 · Opened Sep 16, 2026
Notation for multilinear maps Open

good first issue

Difficulty 2/5 1-3 hours Newbie friendliness 72/100

leanprover-community/mathlib4#43855 · Opened Sep 16, 2026
Bare `⊢ ℝ` unsolved goal when constructing IsPicardLindelof via of_time_independent with NNReal params Open

Difficulty 4/5 3-5 days Newbie friendliness 45/100

leanprover-community/mathlib4#43614 · Opened Sep 9, 2026
Rename `.lipschitz` to `.lipschitzWith` Open

Difficulty 3/5 1-2 days Newbie friendliness 68/100

leanprover-community/mathlib4#42869 · 2 comments · Opened Aug 17, 2026
@[to_dual] fails when a `Decidable` instance's argument is itself an `ite` Open

Difficulty 4/5 3-5 days Newbie friendliness 52/100

leanprover-community/mathlib4#42852 · Opened Aug 17, 2026
agda2lean Open

Difficulty 5/5 Over a week Newbie friendliness 20/100

leanprover-community/mathlib4#42793 · Opened Aug 15, 2026
Missing: Sheppard's formula / Gaussian arcsine law `E[sign X · sign Y] = (2/π) arcsin ρ` Open

Difficulty 5/5 Over a week Newbie friendliness 35/100

leanprover-community/mathlib4#42600 · Opened Aug 10, 2026
docs: update docs with new material Open

documentation

Difficulty 5/5 Over a week Newbie friendliness 20/100

leanprover-community/mathlib4#42593 · Opened Aug 9, 2026
norm_num introduces Classical.choice on order goals over Nat/Int where decide does not Open

Difficulty 4/5 3-5 days Newbie friendliness 55/100

leanprover-community/mathlib4#42565 · 1 comment · Opened Aug 8, 2026
Define a typeclass for GO-space Open

good first issue t-topology

Difficulty 5/5 Over a week Newbie friendliness 48/100

leanprover-community/mathlib4#42275 · 5 comments · 1 reaction · Opened Jul 30, 2026
calc? emits weird dagger characters Open

Difficulty 3/5 1-2 days Newbie friendliness 55/100

leanprover-community/mathlib4#42155 · Opened Jul 27, 2026
deriving CommRing on InfiniteAdeleRing generates opaque _aux_* field definitions that defeat isDefEq at instances transparency Open

Difficulty 4/5 3-5 days Newbie friendliness 25/100

leanprover-community/mathlib4#42057 · Opened Jul 24, 2026
Ideas for contribution by undergraduate computer science students Open

Difficulty 5/5 Over a week Newbie friendliness 25/100

leanprover-community/mathlib4#42039 · 1 comment · Opened Jul 23, 2026
Differential of the determinant Jacobi's formula Open

Difficulty 5/5 Over a week Newbie friendliness 35/100

leanprover-community/mathlib4#41881 · Opened Jul 18, 2026
linarith? fails while linarith finds the proofs Open

leanprover-community/mathlib4#41471 · 2 comments · 1 assignee · Opened Jul 7, 2026
Reviving the `leanprover-community/GameTheory` satellite repo idea (from #13248) Open

Difficulty 5/5 Over a week Newbie friendliness 25/100

leanprover-community/mathlib4#41384 · 1 comment · Opened Jul 5, 2026
Rigidity Equality Open

Difficulty 5/5 Over a week Newbie friendliness 25/100

leanprover-community/mathlib4#40993 · Opened Jun 24, 2026
Header linter can repeatedly reparse Verso document bodies Open

Difficulty 4/5 3-5 days Newbie friendliness 66/100

leanprover-community/mathlib4#40635 · Opened Jun 15, 2026
Morphism classes not used for integration and related issues Open

t-topology

Difficulty 4/5 3-5 days Newbie friendliness 45/100

leanprover-community/mathlib4#40487 · Opened Jun 10, 2026
Add global pull lemmas Open

t-linter

Difficulty 4/5 3-5 days Newbie friendliness 48/100

leanprover-community/mathlib4#40183 · 1 comment · Opened Jun 3, 2026
New tool for splitting up mathlib Open

Difficulty 5/5 Over a week Newbie friendliness 25/100

leanprover-community/mathlib4#40065 · Opened May 31, 2026
Add `PDecidable` (like `Decidable`, but allows arbitrary sorts so it can hold data) Open

Difficulty 4/5 3-5 days Newbie friendliness 45/100

leanprover-community/mathlib4#39751 · Opened May 23, 2026
Algebraic graph theory formalisation: Sabidussi, Lorimer, and the G₂(2) ecosystem Open

Difficulty 5/5 Over a week Newbie friendliness 15/100

leanprover-community/mathlib4#39717 · Opened May 22, 2026
Umbral calculus formalisation: finite operator calculus and Rota's classification Open

Difficulty 5/5 Over a week Newbie friendliness 25/100

leanprover-community/mathlib4#39712 · Opened May 22, 2026
Use `Is*Apply` classes Open

Difficulty 5/5 Over a week Newbie friendliness 25/100

leanprover-community/mathlib4#39639 · Opened May 21, 2026
Nonexistent `SetRel.map` in example Open

Difficulty 2/5 1-3 hours Newbie friendliness 65/100

leanprover-community/mathlib4#39396 · Opened May 14, 2026
API development for `LanguageOn` in symbolic dynamics Open

Difficulty 4/5 3-5 days Newbie friendliness 45/100

leanprover-community/mathlib4#39252 · Opened May 12, 2026
Formalization of various notions of convergence Open

Difficulty 5/5 Over a week Newbie friendliness 25/100

leanprover-community/mathlib4#39125 · 1 reaction · Opened May 9, 2026
Feature Request: Schur complement for block matrices and singular value bounds Open

Difficulty 5/5 Over a week Newbie friendliness 45/100

leanprover-community/mathlib4#38808 · Opened May 1, 2026
Make `scripts/add_deprecations.sh` support additivised declarations Open

enhancement good first issue

Difficulty 3/5 1-2 days Newbie friendliness 68/100

leanprover-community/mathlib4#38550 · 3 comments · 1 reaction · Opened Apr 26, 2026
Weak spaces as a class Open

Difficulty 5/5 Over a week Newbie friendliness 30/100

leanprover-community/mathlib4#38484 · 3 reactions · Opened Apr 24, 2026
Stability under finite-rank perturbation of strict linear maps with closed range Open

enhancement t-analysis t-topology

Difficulty 5/5 Over a week Newbie friendliness 35/100

leanprover-community/mathlib4#38471 · 1 comment · Opened Apr 24, 2026
unused arguments not reported in CategoryTheory Open

Difficulty 3/5 1-2 days Newbie friendliness 45/100

leanprover-community/mathlib4#38299 · 1 comment · Opened Apr 20, 2026
Regression: inferInstance fails for NormSMulClass ℝ ℂ / ContinuousSMul ℝ ℂ in v4.29.0 Open

Difficulty 4/5 3-5 days Newbie friendliness 48/100

leanprover-community/mathlib4#37600 · 2 comments · Opened Apr 3, 2026
GCD of sum and difference Open

Difficulty 3/5 1-2 days Newbie friendliness 52/100

leanprover-community/mathlib4#37366 · 6 comments · Opened Mar 30, 2026
`simps -fullyApplied` should generate `coe_` instead of `_apply` Open

t-meta

Difficulty 5/5 Over a week Newbie friendliness 35/100

leanprover-community/mathlib4#37331 · Opened Mar 29, 2026
`flip` vs `Function.swap` Open

Difficulty 4/5 3-5 days Newbie friendliness 48/100

leanprover-community/mathlib4#36902 · 2 comments · Opened Mar 20, 2026
False positives for `tryAtEachStep` linter and `grind +suggestions` tactic Open

Difficulty 4/5 3-5 days Newbie friendliness 45/100

leanprover-community/mathlib4#36440 · Opened Mar 10, 2026
feat(Algebra/Group): Add translator tactic for Subgroup and subgroupOf Open

Difficulty 5/5 Over a week Newbie friendliness 35/100

leanprover-community/mathlib4#35419 · 4 comments · Opened Feb 16, 2026
feat(Computability): Step counting and complexity classes P/NP for TM1 Open

Difficulty 5/5 Over a week Newbie friendliness 38/100

leanprover-community/mathlib4#35366 · 1 comment · 1 reaction · Opened Feb 15, 2026
Tracking issue: extensions to the unused*In linter Open

Difficulty 4/5 3-5 days Newbie friendliness 35/100

leanprover-community/mathlib4#35340 · Opened Feb 15, 2026
Jordan Curve Theorem (JCT) Open

t-algebraic-topology

Difficulty 5/5 Over a week Newbie friendliness 20/100

leanprover-community/mathlib4#35222 · Opened Feb 13, 2026
Graph theory def: Maximal/maximum cliques & independent sets Open

help-wanted t-combinatorics

Difficulty 3/5 1-2 days Newbie friendliness 55/100

leanprover-community/mathlib4#34962 · 8 comments · Opened Feb 7, 2026
Graph theory def: Edge connectivity number Open

help-wanted t-combinatorics

Difficulty 5/5 Over a week Newbie friendliness 35/100

leanprover-community/mathlib4#34961 · 6 comments · Opened Feb 7, 2026
Graph theory def: Vertex connectivity Open

help-wanted t-combinatorics

Difficulty 5/5 Over a week Newbie friendliness 35/100

leanprover-community/mathlib4#34960 · 1 comment · Opened Feb 7, 2026
Graph theory def: Matching number Open

help-wanted t-combinatorics

leanprover-community/mathlib4#34959 · 6 comments · 1 assignee · Opened Feb 7, 2026
Graph theory def: Minimal/minimum vertex covers Open

help-wanted t-combinatorics

Difficulty 3/5 1-2 days Newbie friendliness 45/100

leanprover-community/mathlib4#34958 · 3 comments · Opened Feb 7, 2026
Graph theory def: Maximal/maximum matchings Open

help-wanted t-combinatorics

Difficulty 4/5 3-5 days Newbie friendliness 45/100

leanprover-community/mathlib4#34957 · 3 comments · Opened Feb 7, 2026

leanprover-community/mathlib4

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