proposition: Lemma msetISS A B C D : A `<=` C -> B `<=` D -> A `&` B `<=` C `&` D.
proof: Proof. by move=> /(msetSI B) /msubset_trans sAC /(msetIS C) /sAC. Qed.
imports: mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop tuple) finmap