Conditional limit
Never seen such a notation.
\documentclass{article}
\usepackage{amsmath}
\makeatletter
\newcommand{\tendstoas}[2]{\mathrel{\tendstoas@{#1}{#2}}}
\newcommand{\tendstoas@}[2]{%
\mathop{%
\vphantom{\big\downarrow}%
\ooalign{$\m@th\longrightarrow$\cr\hfil$\m@th\big\downarrow$\hfil}%
}\limits^{#1}_{#2}%
}
\makeatother
\begin{document}
The expression goes to zero, while $\epsilon$ goes to zero:
\[
\lim_{\epsilon\to0} \left( F(x+\epsilon) - F(x-\epsilon) \right) = 0
\]
Which could be written as:
\[
F(x+\epsilon) - F(x-\epsilon) \tendstoas{\epsilon}{0} 0
\]
\end{document}
Notes: \limits
is redundant in display math mode; $$
should never be used in LaTeX.
Alternatives:
Which could be written as:
\[
F(x+\epsilon) - F(x-\epsilon) \xrightarrow[\epsilon\to0]{} 0
\]
Which could be written as:
\[
F(x+\epsilon) - F(x-\epsilon) \xrightarrow{\epsilon\to0} 0
\]
Following the suggestion of Sebastiano to use a symbol from the STIX2 fonts, namely \tosa
⤩, but rotating it 45 degrees, here's a variant:
\DeclareFontFamily{U}{stix2sf}{}
\DeclareFontShape{U}{stix2sf}{m}{it}{<-> stix2-mathsfit}{}
\newcommand{\tendstoas}[2]{%
\mathrel{%
\mathop{%
\rotatebox[origin=c]{45}{\usefont{U}{stix2sf}{m}{it}\symbol{"C2}}%
}\limits^{#1}_{#2}%
}%
}
\documentclass{article}
\usepackage{stackengine}
\newcommand\condlimit[2]{\mathrel{\ensurestackMath{%
\stackinset{c}{-1.7pt}{c}{-.4pt}{\mathop{\downarrow}\limits^{#1}_{#2}}%
{\rightarrow}}}}
\begin{document}
\[
1 + F(x+\epsilon) - F(x-\epsilon)\condlimit{0}{\epsilon} 1
\]
\end{document}