az7−2a3z5 + 4az5−2z5a−1 + a5z3−6a3z3 + 9az3−4z3a−1 + z3a−3 + 2a5z−9a3z + 8az−3za−1 + 2a5z−1−4a3z−1 + 3az−1−a−1z−1