−z8a−6 + z6a−4−7z6a−6 + z6a−8 + 6z4a−4−16z4a−6 + 6z4a−8 + 10z2a−4−17z2a−6 + 8z2a−8−z2a−10 + 6a−4−9a−6 + 3a−8 + a−4z−2−2a−6z−2 + a−8z−2