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