− a 4 z 8 + a 6 z 6 − 7 a 4 z 6 + 5 a 6 z 4 − 16 a 4 z 4 + z 4 + 7 a 6 z 2 − 12 a 4 z 2 + a 2 z 2 + 3 z 2 + a 6 − 2 a 4 + a 2 + 1 {\displaystyle -a^{4}z^{8}+a^{6}z^{6}-7a^{4}z^{6}+5a^{6}z^{4}-16a^{4}z^{4}+z^{4}+7a^{6}z^{2}-12a^{4}z^{2}+a^{2}z^{2}+3z^{2}+a^{6}-2a^{4}+a^{2}+1}