intros. inv H; reflexivity.
Qed.

(* Specifications: *)
Lemma corestep_not_halted: forall (ge : genv) (m : mem) (q : RTL_core) (m' : mem) (q' : RTL_core),
RTL_corestep ge q m q' m' -> RTL_halted q = None.
Lemma after_xor_at_external: forall (retv : option val) (q q' : RTL_core),
RTL_after_external retv q = Some q' -> RTL_at_external q' = None.