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