#[local]
Hint Immediate MapsTo_1 : core.

(* Specifications: *)
Lemma In_1 :
forall m x y, X.eq x y -> In x m -> In y m.
Lemma In_node_iff :
forall l x e r h y,
In y (Node l x e r h) <-> In y l \/ X.eq y x \/ In y r.