\documentclass[12pt]{article}
\usepackage{amsmath}

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\def\dst{\displaystyle}
\def\LA{\LaTeX}
 \def\ra{\rightarrow}
\def\i{\infty}

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\begin{document}

\centerline {\large LESSON 4: Putting One Thing Over Another }
\vskip.25in

The basic methods for putting things on top of other things in
regular \LA\ goes like the following:

\vskip.1in
\begin{minipage}{2.5in} 
\begin{enumerate}
\item[] \verb+ $\dst \stackrel{a}{b}$+
\item[] \verb+$\dst \overline{\Omega}$+
\item[] \verb+$\dst \underline{W}$+
\end{enumerate}
\end{minipage}
\hspace{.5in}
\begin{minipage}{3in} 
\begin{enumerate}
\item[] $\dst \stackrel{a}{b}$
\item[] $\dst \overline{\Omega}$
\item[] $\dst \underline{W}$
\end{enumerate}

\end{minipage}
 
\vskip.1in

As usual there are other tings available using the
\textit{amsmath} package:

\vskip.1in
\begin{minipage}[t]{2.5in} 
\begin{enumerate}
\item[] \verb+ $\dst \overset{\circ}{\Omega}$+
\item[] \verb+$\dst \underset{\sim}W$+ 
\item[] \verb+$\dst \|f_n-f\|\xrightarrow{n\ra \i }0$+
\vskip.25in

\item[] \verb+$\dst \int\limits_a^b f(x)\, dx$+
\vskip.25in

\item[] \begin{verbatim}
$\dst \sum_{\substack{ 0\le i\le m\\
            0<j<n}} P(i,j)$
\end{verbatim}
\vskip.25in
\item[] \verb+$\dst \sideset{_1^2}{_3^4}\prod$+
\end{enumerate}
\end{minipage}
\hspace{.75in}
\begin{minipage}[t]{3in} 
\begin{enumerate}
\item[]  $\dst \overset{\circ}{\Omega}$
\item[] $\dst \underset{\sim}W$ 
\item[] $\dst \|f_n-f\|\xrightarrow{n\ra \i }0$
\item[] $\dst \int\limits_a^b f(x)\, dx$
\item[] $\dst \sum_{\substack{ 0\le i\le m\\
            0<j<n}} P(i,j)$


\item[] $\dst \sideset{_1^2}{_3^4}\prod$
\end{enumerate}
\end{minipage}
 
 
\vskip.5in
\noindent \textbf{PROBLEM:}   
 
\noindent Give the syntax to create a capital $\Pi$ with a ``tilde'' (see $\sim$ above) over it and a ``bar'' over the tilde.
\vskip.5in

\setlength{\fboxsep}{.75in}
\noindent \framebox[6.6in]{}


\end{document}