proposition: Lemma quotientYidl G : G \subset 'N(H) -> H <*> G / H = G / H.
proof: Proof. by move=> nHG; rewrite joingC quotientYidr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq div) mathcomp(choice fintype prime finset fingroup morphism) mathcomp(automorphism)