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