proposition: Lemma dprodEsd A B : B \subset 'C(A) -> A \x B = A ><| B.
proof: Proof. by rewrite /dprod /cprod => ->. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(choice fintype bigop finset fingroup morphism) mathcomp(quotient action)