Ltac wlt_ind :=
  match goal with
  | [ |- forall (n: word ?len), ?P ] =>
    refine (well_founded_ind (@wlt_wf len) (fun n => P) _)
  end.

Lemma wordToZ_size'': forall (sz : nat), (0 < sz)%nat -> forall w : word sz, (- 2 ^ (Z.of_nat sz - 1) <= wordToZ w < 2 ^ (Z.of_nat sz - 1))%Z.