#[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 find_find : forall m m' x,
find x m = find x m' <->
(forall d, find x m = Some d <-> find x m' = Some d).