− z 2 a 8 − a 8 + z 4 a 6 + 2 z 2 a 6 + z 4 a 4 + 3 z 2 a 4 + 2 a 4 {\displaystyle -z^{2}a^{8}-a^{8}+z^{4}a^{6}+2z^{2}a^{6}+z^{4}a^{4}+3z^{2}a^{4}+2a^{4}}
