proposition: Lemma perm_allLeqE u v a : perm_eq u v -> allLeq u a = allLeq v a.
proof: Proof. Proof using. move=> H; apply/idP/idP; apply: perm_allLeq; first by []. by rewrite perm_sym. Qed.
imports: HB(structures) mathcomp(all_ssreflect) mathcomp(order) tools