mathlib

fb704197 - feat(algebra/group/basic): simplify composed assoc ops (#5031)

feat(algebra/group/basic): simplify composed assoc ops (#5031) New lemmas: `comp_assoc_left` `comp_assoc_right` `comp_mul_left` `comp_add_left` `comp_mul_right` `comp_add_right` Co-authored-by: Yakov Pechersky <pechersky@users.noreply.github.com>