--- a/slides/slides02.tex	Fri Oct 02 07:48:56 2015 +0100
+++ b/slides/slides02.tex	Fri Oct 02 08:48:46 2015 +0100
@@ -228,7 +228,7 @@
 
 \begin{center}
 \bl{$Der\,c\,A \dn \{ s \;|\;  c\!::\!s \in A\}$ } 
-\end{center}\bigskip\bigskip
+\end{center}\bigskip\bigskip\bigskip3
 
 For \bl{$A = \{\textit{foo}, \textit{bar}, \textit{frak}\}$} then
 
@@ -561,7 +561,8 @@
 \item \bl{$Der\,a\,(L(r_1))$}\pause
 \item \bl{$Der\,b\,(Der\,a\,(L(r_1)))$}\pause
 \item \bl{$Der\,c\,(Der\,b\,(Der\,a\,(L(r_1))))$}\bigskip
-\item finally we test whether the empty string is in this set\medskip
+\item finally we test whether the empty string is in this 
+set; same for  \bl{$Ders\,abc\,(L(r_1))$}.\medskip
 \end{enumerate}
 
 The matching algorithm works similarly, just over regular expressions instead of sets.
@@ -636,7 +637,7 @@
 \begin{center}
 \begin{tabular}{rcl}
 \bl{$r$} & \bl{$::=$} & \bl{\ldots}\\
-             & \bl{$\mid$} & \bl{$r\{n\}$}\\
+             & \bl{$\mid$} & \bl{$r^{\{n\}}$}\\
              & \bl{$\mid$} & \bl{$r?$} 
 \end{tabular}
 \end{center}
@@ -734,6 +735,25 @@
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \begin{frame}[t]
+\frametitle{What is good about this Alg.}
+
+\begin{itemize}
+\item extends to most regular expressions, for example
+\bl{$\sim r$}
+
+\item is easy to implement in a functional language
+
+\item the algorithm is already quite old; there is still
+  work to be done to use it as a tokenizer (that is brand new work)
+
+\item we can prove its correctness\ldots
+\end{itemize}
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
 \frametitle{Proofs about Rexps}
 
 Remember their inductive definition:\\[5cm]