proposition: Lemma msetIC (A B : {mset K}) : A `&` B = B `&` A.
proof: Proof. by apply/msetP=> a; rewrite !msetE minnC. Qed.
imports: mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop tuple) finmap