proposition: Lemma normalSG G H : H \subset G -> H <| 'N_G(H).
proof: Proof. by move=> sHG; rewrite /normal subsetI sHG normG subsetIr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)