I have an expression like $G^{\,2,1}_{1,3} \left(\begin{array}{c} a_1\\ b_1,b_2,b_3 \end{array} \middle\vert\ z\right) $, $a_1,b_1,b_2$ and $b_3$ are fixed number.
I want to know $z$ while $G^{\,2,1}_{1,3} \left(\begin{array}{c} a_1\\ b_1,b_2,b_3 \end{array} \middle\vert\ z\right) = \varepsilon $, where $\varepsilon$ is fixed number.
However, I don't know how to solve this equation, please help me with this.
Thanks.