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

Lemma wminus_WS_pos: forall sz (w1 w2: word (S sz)), wordToZ (WS true w1 ^- WS false w2) = (2 * wordToZ (w1 ^- w2) + 1)%Z.