− a 4 z 8 + a 6 z 6 − 7 a 4 z 6 + a 2 z 6 + 5 a 6 z 4 − 17 a 4 z 4 + 4 a 2 z 4 + 7 a 6 z 2 − 15 a 4 z 2 + 4 a 2 z 2 + z 2 + 2 a 6 − 3 a 4 + 2 {\displaystyle -a^{4}z^{8}+a^{6}z^{6}-7a^{4}z^{6}+a^{2}z^{6}+5a^{6}z^{4}-17a^{4}z^{4}+4a^{2}z^{4}+7a^{6}z^{2}-15a^{4}z^{2}+4a^{2}z^{2}+z^{2}+2a^{6}-3a^{4}+2}
