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