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