−z5a−1 + az3−5z3a−1 + z3a−3−z3a−5 + 3az−8za−1 + 6za−3−2za−5 + za−7 + 3az−1−8a−1z−1 + 7a−3z−1−2a−5z−1 + az−3−3a−1z−3 + 3a−3z−3−a−5z−3