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