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

Lemma wminus_minus : forall sz (a b : word sz),
b <= a
-> wordToNat (a ^- b) = wordToNat a - wordToNat b.