−z8a−2−6z6a−2 + 2z6a−4 + z6−15z4a−2 + 8z4a−4−z4a−6 + 4z4−17z2a−2 + 11z2a−4−2z2a−6 + 6z2−7a−2 + 5a−4−a−6 + 4