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