∀ {M : Type u_1} {N : Type u_2} [inst : MulOneClass M] [inst_1 : MulOneClass N] (x y : N),
  Monoid.Coprod.mk (FreeMonoid.of (Sum.inr (x * y))) =
    Monoid.Coprod.mk (FreeMonoid.of (Sum.inr x) * FreeMonoid.of (Sum.inr y))