proposition: Lemma gacentJ A : 'C_(|'J)(A) = 'C(A).
proof: Proof. by rewrite gacentE ?setTI ?subsetT ?afixJ. Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat div seq) mathcomp(fintype bigop finset fingroup morphism perm) mathcomp(automorphism quotient)