This month in mathlib (Apr 2022)
In April 2022 there were 661 PRs merged into mathlib. We list some of the highlights below.

Algebraic geometry

Commutative and linear algebra

Group theory

Analysis

Combinatorics

Many generalizations in the algebra library, dropping commutativity, associativity or unitality hypotheses:
 The generalization linter found many of these generalizations automatically: PR #13092, PR #13094, PR #13095, PR #13099, PR #13100, PR #13106, PR #13107, PR #13109, PR #13252, PR #13260, PR #13443, PR #13657
 Definition of ring homomorphisms and isomorphisms for nonunital (and nonassociative) rings: PR #13430, PR #13626
 Noncommutative modules: PR #13174
 Support for right actions alongside left actions: PR #13257, PR #13362, PR #13475
 Other generalizations in the algebra library: PR #13214, PR #13264, PR #13368, PR #13459
This month we also moved to Lean 3.42.1.