proposition: Lemma is_empty_2 m : is_empty m = true -> Empty m.
proof: Proof. rewrite is_empty_spec. intros H x e. now rewrite <- find_spec, H. Qed.
imports: Coq(Bool Equalities Orders OrdersFacts OrdersLists) Coq(Morphisms Permutation SetoidPermutation) MMaps(Utils Comparisons Interface)