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 : nat) (a b : word sz),
(#b <= #a)%nat ->
#(a ^- b) = #a - #b.