(** Compatibility of evaluation functions with the "less defined than" relation. *)

Ltac TrivialExists :=
  match goal with
  | [ |- exists v, Some ?x = Some v /\ _ ] => exists x; split; auto
  | _ => idtac
  end.

Lemma eval_unop_lessdef: forall op v1 v1' v, eval_unop op v1 = Some v -> Val.lessdef v1 v1' -> exists v', eval_unop op v1' = Some v' /\ Val.lessdef v v'.