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

Lemma wordToZ_wordToN: forall sz (w: word sz), wordToZ w = (Z.of_N (wordToN w) - Z.of_N (if wmsb w false then Npow2 sz else 0))%Z.