proposition: Lemma astabIdom S : 'C_D(S | to) = 'C(S | to).
proof: Proof. by rewrite setIA setIid. Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat div seq) mathcomp(fintype bigop finset fingroup morphism perm) mathcomp(automorphism quotient)