\end{frame}
}
+% Define a new ``partsecframe'' environment that uses a default frame
+% title of ``<part>: <section>'' when no other frame title is given.
+\newenvironment{partsecframe}[1][\insertpart: \insertsectionhead]
+ {\begin{frame}{#1}}
+ {\end{frame}}
+
\mode<all>