$$\tau\tau=\frac{x\epsilon}{\epsilon-x8}$$
$x=\frac{4\pi ^{2}\left(ϵ-x_{8}\right)}{ϵ}$
$ϵ\neq 0\text{ and }ϵ\neq x_{8}$
$x_{8}=-\frac{xϵ}{4\pi ^{2}}+ϵ$
$ϵ\neq 0\text{ and }x\neq 0$
