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

Lemma eq_rect_2: forall sz (pa: word sz) sz' Heq1 Heq2, eq_rect sz' word (eq_rect sz word pa sz' Heq1) sz Heq2 = pa.