mathlib

a0aee51a - chore({group,ring}_theory/sub{group,monoid,ring,semiring}): Add missing scalar action typeclasses (#8731)

chore({group,ring}_theory/sub{group,monoid,ring,semiring}): Add missing scalar action typeclasses (#8731) This adds `has_faithful_scalar` and `mul_semiring_action` instances for simple subtypes. Neither typeclass associates any new actions with these types; they just provide additionally properties of the existing actions.