z 4 − a 2 z 2 − z 2 a 2 + 3 z 2 − a 2 − 1 a 2 + 3 {\displaystyle z^{4}-a^{2}z^{2}-{\frac {z^{2}}{a^{2}}}+3z^{2}-a^{2}-{\frac {1}{a^{2}}}+3}
