−z8a−2−5z6a−2 + 2z6a−4 + z6−11z4a−2 + 6z4a−4−z4a−6 + 3z4−10z2a−2 + 7z2a−4−z2a−6 + 4z2−3a−2 + 3a−4−a−6 + 2