proposition: Lemma msetUS C A B : A `<=` B -> C `|` A `<=` C `|` B.
proof: Proof. move=> sAB; apply/msubsetP=> x; rewrite !msetE. by rewrite geq_max !leq_max leqnn (msubsetP sAB) orbT. Qed.
imports: mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop tuple) finmap