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