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

Lemma pow2_wneg: forall sz, wneg (natToWord (S sz) (pow2 sz)) = natToWord (S sz) (pow2 sz).