proposition: Lemma gacentY A B : A \subset D -> B \subset D -> 'C_(|to)(A <*> B) = 'C_(|to)(A) :&: 'C_(|to)(B).
proof: Proof. by move=> sAD sBD; rewrite gacent_gen ?gacentU // subUset sAD. Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat div seq) mathcomp(fintype bigop finset fingroup morphism perm) mathcomp(automorphism quotient)