proposition: Lemma slt_filter (p : pred A) ks x y : (x \notin ks) || p x -> (y \notin ks) || p y -> x <[filter p ks] y = x <[ks] y.
proof: Proof. by move=>H1 H2; apply/idP/idP; [apply: slt_filterR | apply: slt_filterL]. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path interval order) pcm(options prelude ordtype seqext)