az7−2a3z5 + 4az5−2z5a−1 + a5z3−6a3z3 + 8az3−5z3a−1 + z3a−3 + 2a5z−7a3z + 8az−4za−1 + za−3 + a5z−1−3a3z−1 + 4az−1−2a−1z−1