$\left\{\begin{matrix}x=q^{-\frac{1}{2}}\xi _{1}\text{, }y=q^{-\frac{1}{2}}\xi _{1}\text{, }&q\neq 0\\x=y\text{, }y\in \mathrm{C}\text{, }&\xi _{1}=0\text{ and }q=0\end{matrix}\right.$

$\left\{\begin{matrix}x=\frac{\xi _{1}}{\sqrt{q}}\text{, }y=\frac{\xi _{1}}{\sqrt{q}}\text{, }&q>0\\x=y\text{, }y\in \mathrm{R}\text{, }&q=0\text{ and }\xi _{1}=0\end{matrix}\right.$