proposition: Lemma group_set_diso3 : group_set dir_iso3.
proof: Proof. apply/group_setP; split; first by rewrite inE eqxx /=. by apply: stable. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(choice fintype tuple finfun bigop finset fingroup) mathcomp(action perm primitive_action)