(** *Diagrams for machine steps*)

Lemma strong_tree_leq_xmap:
forall {A B} f1 f2 t (leq: option B -> option A -> Prop),
(forall a p, leq (Some (f1 p a)) (Some (f2 p a))) ->
leq None None ->
forall p,
bounded_maps.strong_tree_leq
(PTree.xmap f1 t p)
(@PTree.xmap A A f2 t p)
leq.