proposition: Lemma sub_abelian_normal : (C \subset A) = (C <| A).
proof: Proof. by rewrite /normal; case sHG: (C \subset A); rewrite // sub_abelian_norm. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)