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