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

Lemma induct_word_S: forall (P : forall n : nat, word (S n) -> Prop), (forall b, P 0 (WS b WO)) -> (forall b b0 n (w : word n), P n (WS b0 w) -> P (S n) (WS b (WS b0 w))) -> forall (n : nat) (w : word (S n)), P n w.