proposition: Lemma gacentIdom : 'C_(|to)(D :&: A) = 'C_(|to)(A).
proof: Proof. by rewrite /gacent setIA setIid. Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat div seq) mathcomp(fintype bigop finset fingroup morphism perm) mathcomp(automorphism quotient)