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