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