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\begin{document}

See Figure~\ref{arch1} for an overview of the Simplicissimus
architecture.
\begin{figure}[htb]
\begin{center}
\includegraphics[height=3in,width=4in]{Architecture}
\caption{A user expression, translated into Gnu's abstract
syntax tree (upper box), mapped to the internal representation
in Simplicissimus, rewritten by the core engine (lower box), 
and mapped back.}
\label{arch1}
\end{center}
\end{figure}

In Figure~\ref{arch2} we have the same diagram but it's reconfigured a
bit.
\begin{figure}[htb]
\begin{center}
\includegraphics[height=5in,width=4in,angle=90]{Architecture}
\caption{Same diagram as in Figure~\ref{arch1}, but 
drawn a little larger, stretched in one dimension, and rotated 90
degrees counterclockwise.}
\label{arch2}
\end{center}
\end{figure}

\end{document}