proposition: Lemma subcent_normal G B : 'C_G(B) <| 'N_G(B).
proof: Proof. by rewrite /normal subcent_sub subcent_norm. Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(fintype bigop finset fingroup morphism perm) mathcomp(automorphism quotient action gproduct gfunctor) mathcomp(cyclic)