#[local]
Hint Resolve lt_tree_not_in lt_tree_trans gt_tree_not_in gt_tree_trans : core.
(** * Empty map *)
Definition Empty m := forall (a:key)(e:elt) , ~ MapsTo a e m.

Lemma not_find_iff : forall m x, bst m ->
(find x m = None <-> ~In x m).