−az7−z7a−1−a2z6−3z6a−2−4z6−a3z5−3z5a−1−4z5a−3 + a2z4 + 2z4a−2−3z4a−4 + 6z4 + 4a3z3 + 5az3 + 6z3a−1 + 4z3a−3−z3a−5 + 3a2z2 + z2a−2 + 2z2a−4 + 2z2−5a3z−6az−2za−1−za−3−3a2−a−2−3 + 2a3z−1 + 3az−1 + a−1z−1