End FORWARD_TO_BACKWARD.
(** The backward simulation *)

(* Specifications: *)
Lemma forward_to_backward_simulation:
forall L1 L2,
forward_simulation L1 L2 -> receptive L1 -> determinate L2 ->
backward_simulation L1 L2.
Lemma forward_to_backward_simulation:
forall L1 L2,
forward_simulation L1 L2 -> receptive L1 -> determinate L2 ->
backward_simulation L1 L2.