proposition: Lemma msetUidPl A B : reflect (A `|` B = A) (B `<=` A).
proof: Proof. by rewrite msetUC; apply/msetUidPr. Qed.
imports: mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop tuple) finmap