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