a 8 − 2 z 2 a 6 − 2 a 6 + z 4 a 4 + 2 z 2 a 4 + a 4 − z 2 a 2 + 1 {\displaystyle a^{8}-2z^{2}a^{6}-2a^{6}+z^{4}a^{4}+2z^{2}a^{4}+a^{4}-z^{2}a^{2}+1}
