\begin{frame}
\small

\vspace{-1ex}

\begin{block}{Summary}
\begin{center}
\begin{tikzpicture}[on grid,node distance=16mm and 29mm]
\node (1)                                {\alert<1-6>{CR}};
\node (2) [above left=of 1]              {\alert<1,5,6>{SN}};
\node (3) [above right=of 1]             {\alert<1-4,6>{WN}};
\node (4) [below left=of 1]              {\alert<1,3-4,6>{WCR}};
\node (5) [below right=of 1,xshift=-11mm]             {\alert<1,3-4,6>{NF}};
\begin{scope}[node distance=11mm]
\node (5') [right=of 5]                  {\alert<1,3-4,6>{\UN}};
\node (5'') [right=of 5']                {\alert<1,3-4,6>{\UNrew}};
\end{scope}
\node (6) [node distance=2cm,left=of 1]  {\&};
\node (7) [node distance=2cm,right=of 1] {\&};
\draw[->] (1) edge[bend left]           (4);
\draw[->] (1) edge[bend right]          (5);
\draw[->] (2) edge                      (3);
\draw[->] (2) edge[bend right]          (1);
\draw[->] (3) edge[bend left]           (1);
\draw[->] (4) edge[bend left]           (1);
\draw[->] (5'') edge[bend right=20]        (1);
\draw[->] (5) edge                      (5');
\draw[->] (5') edge                     (5'');
\end{tikzpicture}
\end{center}
\end{block}

\begin{definitions}<2->
\begin{itemize}
\item
\makebox[3cm][l]{\alert<2-4>{semi-completeness}}
\begin{itemize}
\item
CR \& WN
\item<4->
every element has unique normal form
\end{itemize}
\item<5->
\makebox[3cm][l]{\alert<5,6>{completeness}}
\begin{itemize}
\item
CR \& SN
\smallskip
\end{itemize}
\end{itemize}
\end{definitions}

\end{frame}