proposition: Lemma ltn_sorted_uniq_leq s : sorted ltn s = uniq s && sorted leq s.
proof: Proof. rewrite (sorted_pairwise leq_trans) (sorted_pairwise ltn_trans) uniq_pairwise. by rewrite -pairwise_relI; apply/eq_pairwise => ? ?; rewrite ltn_neqAle. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq)