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

Lemma wordToZ_wordToNat_pos: forall sz (w: word sz), wmsb w false = false -> Z.of_nat (wordToNat w) = wordToZ w.