−z7a−1 + 2az5−4z5a−1 + 2z5a−3−a3z3 + 6az3−9z3a−1 + 5z3a−3−z3a−5−2a3z + 8az−10za−1 + 5za−3−za−5−a3z−1 + 4az−1−4a−1z−1 + a−3z−1