proposition: Lemma slt_catL ks1 ks2 x y : x <[ks1] y -> x <[ks1++ks2] y.
proof: Proof. by move=>H; rewrite slt_cat H (slt_memE H) if_same. Qed.
imports: Coq(ssreflect ssrbool ssrfun) mathcomp(ssrnat eqtype seq path interval order) pcm(options prelude ordtype seqext)