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