proposition: Lemma normalD1 A G : (A^# <| G) = (A <| G).
proof: Proof. by rewrite /normal normD1 subDset (setUidPr (sub1G G)). Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)