az7−a3z5 + 5az5−2z5a−1−4a3z3 + 9az3−7z3a−1 + z3a−3 + a5z−5a3z + 7az−7za−1 + 2za−3 + a5z−1−2a3z−1 + 3az−1−3a−1z−1 + a−3z−1