proposition: Lemma quotientMr A B : B \subset 'N(H) -> A * B / H = (A / H) * (B / H).
proof: Proof. exact: morphimMr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq div) mathcomp(choice fintype prime finset fingroup morphism) mathcomp(automorphism)