−z6a−4−z6a−6 + z4a−2−3z4a−4−3z4a−6 + 2z4a−8 + 3z2a−2−z2a−4−2z2a−6 + 6z2a−8−z2a−10 + a−2−a−6 + 3a−8−2a−10