∀ {R : Type u} [inst : CommRing R] {A B C D : CommAlgCat R} (f : A ⟶ C) (g : B ⟶ D),
  CommAlgCat.Hom.hom (CategoryTheory.MonoidalCategoryStruct.tensorHom f g) =
    Algebra.TensorProduct.map (CommAlgCat.Hom.hom f) (CommAlgCat.Hom.hom g)