∀ {R : Type u_1} {A : Type u_2} {B : Type u_3} {C : Type u_4} [inst : CommSemiring R] [inst_1 : Semiring A]
  [inst_2 : Algebra R A] [inst_3 : Semiring B] [inst_4 : Algebra R B] [inst_5 : Semiring C] [inst_6 : Algebra R C]
  (f : A →ₐ[R] B) (g : A →ₐ[R] C), ⇑(f.prod g) = Pi.prod ⇑f ⇑g