proposition: Lemma sub_abelian_norm : C \subset A -> A \subset 'N(C).
proof: Proof. by move=> sCA; rewrite cents_norm ?sub_abelian_cent. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)