proposition: Lemma sorted_sle ks : uniq ks -> sorted (seq_le ks) ks.
proof: Proof. move=>U; apply: sub_sorted (sorted_slt U). by move=>x y; rewrite /seq_lt/seq_le; case: ltngtP. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path interval order) pcm(options prelude ordtype seqext)