proposition: Lemma subcent_norm G B : 'N_G(B) \subset 'N('C_G(B)).
proof: Proof. by rewrite normsI ?subIset ?normG // orbC cent_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)