− a 10 + z 2 a 8 + a 8 − a 6 + z 4 a 4 + 4 z 2 a 4 + 2 a 4 {\displaystyle -a^{10}+z^{2}a^{8}+a^{8}-a^{6}+z^{4}a^{4}+4z^{2}a^{4}+2a^{4}}
