proposition: Lemma subcent_sub A B : 'C_A(B) \subset 'N_A(B).
proof: Proof. by rewrite setIS ?cent_sub. 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)