$\left\{\begin{matrix}ϵ\in \left(\frac{C}{u},0\right)\text{, }&C>0\text{ and }u<0\\ϵ\in \left(0,\frac{C}{u}\right)\text{, }&C<0\text{ and }u<0\\ϵ<\frac{C}{u}\text{, }&u>0\text{ and }C<0\\ϵ\neq 0\text{, }&C=0\text{ and }u>0\\ϵ>\frac{C}{u}\text{, }&u>0\text{ and }C>0\\ϵ>0\text{, }&u\geq 0\text{ and }C<0\\ϵ<0\text{, }&C>0\text{ and }u\geq 0\end{matrix}\right.$

$u>\frac{C}{ϵ}$
$ϵ\neq 0$