Definition is_true (b: bool) :=
  match b with true => True | false => False end.Definition force_val (v: option val) : val :=
 match v with Some v' => v' | None => Vundef end.Definition force_val1 (f: val -> option val) (v: val) := force_val (f v).Definition force_val2 (f: val -> val -> option val) (v1 v2: val) := force_val (f v1 v2).Definition force_int (v: val) :=
 match v with
 | Vint i => i | _ => Int.zero
 end.Definition force_signed_int v := Int.signed (force_int v).

Lemma force_Vint: forall i, force_int (Vint i) = i.