proposition: Lemma msetBDr C A B : (A `+` C) `\` (B `+` C) = A `\` B.
proof: Proof. by apply/msetP=> a; rewrite !msetE subnDr. Qed.
imports: mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop tuple) finmap