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

Lemma wmsb_1_natToWord: forall sz n default, pow2 sz <= n < 2 * pow2 sz -> @wmsb (S sz) (natToWord (S sz) n) default = true.