proposition: Lemma msubsetDl A B : A `\` B `<=` A.
proof: Proof. by apply/msubsetP=> x; rewrite msetE leq_subLR leq_addl. Qed.
imports: mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop tuple) finmap