proposition: Lemma mset_eqP {A B} : reflect (A =1 B) (A == B).
proof: Proof. exact: (equivP eqP (iff_sym msetP)). Qed.
imports: mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop tuple) finmap