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