در تابع با ضابطهی $f\left( x \right)=\left\{ \begin{matrix}
\sqrt{1-x}\,\,\,\,\,\,\,\,\,\,;\,\,\,\,\,\,\,x\gt 0 \\
-\sqrt{1+x}\,\,\,\,\,\,\,\,\,;\,\,\,\,\,\,\,x\le 0 \\
\end{matrix} \right.$، حاصل $\underset{x\to {{0}^{-}}}{\mathop{\lim }}\,f\left( {{x}^{3}}-x \right)$ کدام است؟