proposition: Lemma quotientSK A B : A \subset 'N(H) -> (A / H \subset B / H) = (A \subset H * B).
proof: Proof. by move=> nHA; rewrite morphimSK ?ker_coset. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq div) mathcomp(choice fintype prime finset fingroup morphism) mathcomp(automorphism)