∀ {ι : Type u_1} {ι₂ : Type u_2} (R : Type u_4) [inst : CommSemiring R] (M : Type u_8) [inst_1 : AddCommMonoid M]
  [inst_2 : Module R M] (a : ι ⊕ ι₂ → M),
  (PiTensorProduct.tmulEquiv R M).symm ((PiTensorProduct.tprod R) fun i => a i) =
    ((PiTensorProduct.tprod R) fun i => a (Sum.inl i)) ⊗ₜ[R] (PiTensorProduct.tprod R) fun i => a (Sum.inr i)