az7−a3z5 + 4az5−2z5a−1−3a3z3 + 6az3−6z3a−1 + z3a−3 + a5z−4a3z + 5az−6za−1 + 2za−3 + a5z−1−2a3z−1 + 3az−1−3a−1z−1 + a−3z−1