(** * Safe executions. *)

(** A state is safe according to the nondeterministic semantics
  if it cannot get stuck by doing silent transitions only. *)

Definition safe (s: Csem.state) : Prop :=
  forall s', star Csem.step ge s E0 s' ->
  (exists r, final_state s' r) \/ (exists t, exists s'', Csem.step ge s' t s'').

Lemma safe_steps: forall s s', safe s -> star Csem.step ge s E0 s' -> safe s'.