proposition: Lemma msetUA A B C : A `|` (B `|` C) = A `|` B `|` C.
proof: Proof. by apply/msetP=> x; rewrite !msetE maxnA. Qed.
imports: mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop tuple) finmap