Here is the code of the file:

--8<---------------cut here---------------start------------->8---
\documentclass[10pt]{article}

\usepackage{amsmath}

\begin{document}

\begin{verbatim}
(setq LaTeX-fold-math-spec-list
      (append '(("[{1}/{2}]"
                 ("frac" "tfrac"))
                ("[{1}⇣{2}]"
                 ("underset"))
                ("[{1}⇡{2}]"
                 ("overset"))
                ("√[{1}]"
                 ("sqrt")))
              LaTeX-fold-math-spec-list))
\end{verbatim}

$\frac{1}{2} \tfrac{1}{2} \overset{1}{2}
\underset{\hslash\to 0}{ \longrightarrow}
\sqrt{9}$

\end{document}
--8<---------------cut here---------------end--------------->8---

What I did was:
1) Open a new tex file
2) Eval the setq form (put cursor after the last parenthesis and hit
`C-x C-e'
3) Hitting `M-x TeX-fold-mode RET' and `C-c C-o C-b'.

Best, Arash