∀ {R : Type u_2} {A : Type u_1} [inst : CommSemiring R] [inst_1 : Semiring A] [inst_2 : Algebra R A]
  (S : Subalgebra R A) (x y : ↥S.toSubsemiring),
  S.ringEquivOpMop.toFun (x * y) = S.ringEquivOpMop.toFun x * S.ringEquivOpMop.toFun y