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

Lemma wminus_wneg: forall sz (w1 w2: word sz), wneg (w1 ^- w2) = w2 ^- w1.