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