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