z 6 a 2 + 5 z 4 a 2 − z 4 a 4 − z 4 + 9 z 2 a 2 − 3 z 2 a 4 − 3 z 2 + 6 a 2 − 3 a 4 − 2 {\displaystyle {\frac {z^{6}}{a^{2}}}+{\frac {5z^{4}}{a^{2}}}-{\frac {z^{4}}{a^{4}}}-z^{4}+{\frac {9z^{2}}{a^{2}}}-{\frac {3z^{2}}{a^{4}}}-3z^{2}+{\frac {6}{a^{2}}}-{\frac {3}{a^{4}}}-2}
