End CombineList.

Lemma shift_two_8 z:
match z with
| 0 => 0
| Z.pos y' => Z.pos y'~0~0~0~0~0~0~0~0
| Z.neg y' => Z.neg y'~0~0~0~0~0~0~0~0
end = (z * two_p 8)%Z.