proposition: Lemma normalYl G H : (H <| H <*> G) = (G \subset 'N(H)).
proof: Proof. by rewrite /normal joing_subl join_subG normG. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)