∀ {R : Type u_1} [inst : NonAssocSemiring R] (S : Subsemiring R) (x x_1 : ↥S),
  (S.addEquivOp.trans MulOpposite.opAddEquiv).toFun (x * x_1) =
    (S.addEquivOp.trans MulOpposite.opAddEquiv).toFun (x * x_1)