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

Lemma NToWord_WS_0: forall sz n, NToWord (S sz) (2 * n) = (NToWord sz n)~0.