$\left\{\begin{matrix}x<\frac{2}{y}\text{, }&y<0\\x>\frac{2}{y}\text{, }&y>\frac{1}{2}\end{matrix}\right.$

$\left\{\begin{matrix}y>\frac{2}{x}\text{, }&x>0\text{ and }x<4\\y>\frac{1}{2}\text{, }&x\geq 4\\y<\frac{2}{x}\text{, }&x<0\end{matrix}\right.$