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

Lemma wmsb_split2': forall sz (w: word (S sz)) b, wmsb w b = negb (weqb (split2 sz 1 (nat_cast _ (eq_sym (Nat.add_1_r sz)) w)) (natToWord _ 0)).