proposition: Lemma not_mem_find m x : mem x m = false <-> find x m = None.
proof: Proof. rewrite <- not_mem_in_iff. apply not_in_find. Qed.
imports: Coq(Bool Equalities Orders OrdersFacts OrdersLists) Coq(Morphisms Permutation SetoidPermutation) MMaps(Utils Comparisons Interface)