proposition: Lemma dir_iso_iso3 : forall p, p \in dir_iso3 -> is_iso3 p.
proof: Proof. move=> p; rewrite inE. by do ?case/orP; move/eqP=> <- a; rewrite !permE; case: a; do 6?case. 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)