proposition: Lemma gacentC A S : A \subset D -> S \subset R -> (S \subset 'C_(|to)(A)) = (A \subset 'C(S | to)).
proof: Proof. by move=> sAD sSR; rewrite subsetI sSR astabCin // (setIidPr sAD). Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat div seq) mathcomp(fintype bigop finset fingroup morphism perm) mathcomp(automorphism quotient)