z12a−12 + 12z10a−12−z10a−14 + 55z8a−12−11z8a−14 + 121z6a−12−44z6a−14 + z6a−16 + 132z4a−12−78z4a−14 + 6z4a−16 + 66z2a−12−60z2a−14 + 10z2a−16 + 12a−12−16a−14 + 5a−16