proposition: Lemma msetUAC A B C : A `|` B `|` C = A `|` C `|` B.
proof: Proof. by rewrite -!msetUA (msetUC B). Qed.
imports: mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop tuple) finmap