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

Lemma wmsb_combine_existT: (* Note: not axiom free *) forall sz (w: word sz) sz1 (w1: word sz1) sz2 (w2: word sz2) b1 b2, sz2 <> 0 -> existT word _ w = existT word _ (combine w1 w2) -> wmsb w b1 = wmsb w2 b2.