−2z4a−2 + z4a−4−z4 + a2z2−8z2a−2 + 6z2a−4−z2a−6−z2 + a2−11a−2 + 9a−4−2a−6 + 3−5a−2z−2 + 4a−4z−2−a−6z−2 + 2z−2