Question about left and right derivative.
Posted by Learning, at math.stackexchange.com,
Let $f(x):\mathbb{R}\rightarrow\mathbb{R}$ be a function such that $\forall x\in\mathbb{R}$ there exist: $$f'_+(x)=\lim_{\delta…
Let $f(x):\mathbb{R}\rightarrow\mathbb{R}$ be a function such that $\forall x\in\mathbb{R}$ there exist: $$f'_+(x)=\lim_{\delta…
Could you help, please. I need the information about the ultrafilters, namely, any ideas how one can see that they exist and a…