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

Lemma wordToNat_eq_rect: forall sz (w: word sz) nsz Hsz, wordToNat (eq_rect _ word w nsz Hsz) = wordToNat w.