proposition: Lemma rot_r1 : forall r, is_rot r -> r = r1 ^+ (r c0).
proof: Proof. move=> r hr; apply: rot_eq_c0 => //; apply/eqP. by symmetry; apply: commuteX. by case: (r c0); do 4?case=> //=; rewrite ?permM !permE /=. 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)