proposition: Lemma le_sorted_filter a s : sorted <=%O s -> sorted <=%O (filter a s).
proof: Proof. exact/sorted_filter/le_trans. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)