Assume that $f_k=f(k \geq 0), 0$ is in the interior of $X$, and $f$ is Fréchet differentiable at 0 . Furthermore, the special radius of $f^{\prime}(0)$ is less than 1. Then show that there is a neighborhood $U$ of 0 such that $x_0 \in U$ implies that $x_k \rightarrow 0$ as $k \rightarrow \infty$.