(** A state can "crash the world" if it can make an observable transition
  whose trace is not accepted by the external world. *)

Definition can_crash_world (w: world) (S: state) : Prop :=
  exists t, exists S', Csem.step ge S t S' /\ forall w', ~possible_trace w t w'.

Theorem not_imm_safe_t: forall K C a m f k, context K RV C -> ~imm_safe_t K a m -> Csem.step ge (ExprState f (C a) k e m) E0 Stuckstate \/ can_crash_world w (ExprState f (C a) k e m).