intro.
rewrite (shatter_word a).
replace (wtl a) with WO by auto.
destruct (whd a).
right; apply eq_refl.
left; apply eq_refl.
Defined.

Lemma weq_minus1_wlt: forall sz (a b : word sz),
(a <> $0 -> a ^- $1 = b -> a > b)%word.