mathlib

76de6f75 - feat(group_theory/subsemigroup/operations): port from submonoid (#12112)

feat(group_theory/subsemigroup/operations): port from submonoid (#12112) Taken from `group_theory.submonoid.operations`, trying to keep as much API as possible Co-authored-by: Jireh Loreaux <loreaujy@gmail.com> Co-authored-by: Jireh Loreaux <loreaujy@gmail.com>