proposition: Lemma iso0_1 : dir_iso3 =i dir_iso3l.
proof: Proof. by move=> p; rewrite /= !inE /= -!(eq_sym p). 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)