∀ {R : Type u_1} {M : Type u_2} [inst : CommSemiring R] [inst_1 : AddCommMonoid M] [inst_2 : Module R M] {i j : ℕ}
  (a : TensorPower R i M) (b : TensorPower R j M), GradedMonoid.GMul.mul a b = TensorPower.mulEquiv (a ⊗ₜ[R] b)