proposition: Lemma has_ou t (ks : seq A) : uniq ks -> has predT (&=ks `]t, +oo[) = has (fun z => t <[ks] z) ks.
proof: Proof. by move/has_predT_uslice=>->; apply: eq_has=>z; rewrite in_itv /= andbT. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path interval order) pcm(options prelude ordtype seqext slice useqord)