z9a−1−az7 + 6z7a−1−z7a−3−4az5 + 12z5a−1−4z5a−3−4az3 + 7z3a−1−4z3a−3 + az−3za−1 + za−3 + 2az−1−3a−1z−1 + a−3z−1