End DETERMINACY.
(** * Backward simulations between two transition semantics. *)
Definition safe (L: semantics) (s: state L) : Prop :=
forall s',
Star L s E0 s' ->
(exists r, final_state L s' r)
\/ (exists t, exists s'', Step L s' t s'').

(* Specifications: *)
Lemma star_safe:
forall (L: semantics) s s',
Star L s E0 s' -> safe L s -> safe L s'.