proposition: Lemma Alt_norm : 'Sym_T \subset 'N('Alt_T).
proof: Proof. by case/andP: Alt_normal. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(div fintype tuple tuple bigop prime finset fingroup) mathcomp(morphism perm automorphism quotient action cyclic) mathcomp(pgroup gseries sylow primitive_action)