Theorem Algebra_Hom_compose_assoc {alg alg' alg'' alg''' : Algebra} (f : Algebra_Hom alg alg') (g : Algebra_Hom alg' alg'') (h : Algebra_Hom alg'' alg''') : (Algebra_Hom_compose f (Algebra_Hom_compose g h)) = (Algebra_Hom_compose (Algebra_Hom_compose f g) h).