proposition: Lemma iso3_ndir : forall p, p \in dir_iso3 -> is_iso3 (s0 * p).
proof: Proof. move=> p; rewrite inE. by do ?case/orP; move/eqP=> <- a; rewrite !(permM, 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)