proposition: Lemma msetn0 (a : K) : msetn 0 a = mset0.
proof: Proof. by apply/msetP=> i; rewrite !msetE if_same. Qed.
imports: mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop tuple) finmap