z6a−6 + 3z6a−8 + z6a−10 + 3z4a−6 + 13z4a−8 + z4a−10−z4a−12 + z2a−6 + 16z2a−8−6z2a−10−2z2a−12 + 6a−8−6a−10 + a−12