proposition: Lemma msetUCA A B C : A `|` (B `|` C) = B `|` (A `|` C).
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