True/False Question:
Let $f:\mathbb{R}\rightarrow \mathbb{R}$ be a function such that
$$\underset{h\rightarrow 0}{lim }\:\frac{f\left ( x+h \right )-f\left ( x-h \right )}{h}$$
exists for all $x \in \mathbb{R}$. Then $f$ is differentiable in $\mathbb{R}.$