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: forall sz1 sz2 (w1: word sz1) (w2: word sz2) b1 b2, sz2 <> 0 -> wmsb (combine w1 w2) b1 = wmsb w2 b2.