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RFC: generalize basic Inhabited/Nonempty instances from Monad to Applicative

RFCRequest for commentsRequest for comments

Status: Open.

#12042 In leanprover/lean4;

· fgdorais opened on Jan 19, 2026

Module system breaks tactic completion

bugSomething isn't workingSomething isn't working

Status: Open.

#12038 In leanprover/lean4;

· lua-vr opened on Jan 18, 2026

simp attribute + unknown identifiers = internal exception #3 / PANIC at Lean.MetavarContext.getDecl Lean.MetavarContext:448:17: unknown metavariable

bugSomething isn't workingSomething isn't working

Status: Open.

#12020 In leanprover/lean4;

· Julian opened on Jan 15, 2026

lake update nonexistant-pkgs does not complain

bugSomething isn't workingSomething isn't working

Status: Open.

#12005 In leanprover/lean4;

· nomeata opened on Jan 14, 2026

<code>ungrind</code> mode error message refers to non-existent <code>show_patterns</code> tactic

bugSomething isn't workingSomething isn't working

Status: Open.

#11996 In leanprover/lean4;

· datokrat opened on Jan 13, 2026

Ill-typed <code>match</code> motive inference

bugSomething isn't workingSomething isn't working

Status: Open.

#11995 In leanprover/lean4;

· sgraf812 opened on Jan 13, 2026

grind: normalization of <code>UInt16.toNat 0</code> gets in the way

bugSomething isn't workingSomething isn't working

Status: Open.

#11990 In leanprover/lean4;

· abentkamp opened on Jan 13, 2026

<code>Meta.check</code> Fails After <code>revert</code>

bugSomething isn't workingSomething isn't working

Status: Open.

#11978 In leanprover/lean4;

· lenianiva opened on Jan 12, 2026

Syntax match strange error

bugSomething isn't workingSomething isn't working

Status: Open.

#11951 In leanprover/lean4;

· PatrickMassot opened on Jan 9, 2026

'import all' sometimes still requires @[expose] when using grind

bugSomething isn't workingSomething isn't working

Status: Open.

#11948 In leanprover/lean4;

· cmlsharp opened on Jan 9, 2026

<code>match</code> generalization failure

bugSomething isn't workingSomething isn't working

Status: Open.

#11942 In leanprover/lean4;

· sgraf812 opened on Jan 8, 2026

leanchecker: mention declaration name in error

bugSomething isn't workingSomething isn't working

Status: Open.

#11937 In leanprover/lean4;

· nomeata opened on Jan 8, 2026