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

Lemma wmsb_nat_cast: forall sz1 (w: word sz1) sz2 (Hsz: sz1 = sz2) b, wmsb w b = wmsb (nat_cast word Hsz w) b.