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

Theorem wnot_wrshift : forall sz (w : word sz) n,
wnot (wrshift w n) = split2 n sz (eq_rect _ word (combine (wnot w) (wones n)) _ (eq_sym (Nat.add_comm n sz))).