proposition: Lemma cardinal_inv_in m : cardinal m <> 0 -> { k | In k m }.
proof: Proof. intros H. destruct (cardinal_inv_2b H) as ((k,e),M). simpl in *. exists k. now exists e. Qed.
imports: Coq(Bool Equalities Orders OrdersFacts OrdersLists) Coq(Morphisms Permutation SetoidPermutation) MMaps(Utils Comparisons Interface)