proposition: Lemma normalY G A B : A <| G -> B <| G -> A <*> B <| G.
proof: Proof. by case/andP=> sAG ? /andP[sBG ?]; rewrite /normal join_subG sAG sBG ?normsY. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)