− a 12 + z 2 a 10 + a 10 − a 8 + z 4 a 6 + 3 z 2 a 6 + a 6 + z 4 a 4 + 3 z 2 a 4 + a 4 {\displaystyle -a^{12}+z^{2}a^{10}+a^{10}-a^{8}+z^{4}a^{6}+3z^{2}a^{6}+a^{6}+z^{4}a^{4}+3z^{2}a^{4}+a^{4}}
