--- a/slides/slides02.tex	Sun Sep 27 09:15:32 2020 +0100
+++ b/slides/slides02.tex	Tue Sep 29 00:51:43 2020 +0100
@@ -456,6 +456,7 @@
 
 \begin{center}
 \begin{mybox3}{}
+\centering    
 \bl{$\textit{matcher}\,r\,s \dn \textit{nullable}(\ders\;s\;r)$}
 \end{mybox3}
 \end{center}
@@ -521,6 +522,40 @@
 \end{frame}
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[c]
+\frametitle{\boldmath\;$a^{?\{n\}} \cdot a^{\{n\}}$}
+
+\begin{center}
+\begin{tikzpicture}
+\begin{axis}[
+    xlabel={$n$},
+    x label style={at={(1.05,0.0)}},
+    ylabel={time in secs},
+    enlargelimits=false,
+    xtick={0,5,...,30},
+    xmax=31,
+    ytick={0,5,...,30},
+    scaled ticks=false,
+    axis lines=left,
+    width=7cm,
+    height=7cm, 
+    legend entries={Python,Ruby},  
+    legend pos=outer north east,
+    legend cell align=left  
+]
+\addplot[blue,mark=*, mark options={fill=white}] 
+  table {re-python.data};
+\addplot[brown,mark=pentagon*, mark options={fill=white}] 
+  table {re-ruby.data};    
+\end{axis}
+\end{tikzpicture}
+\end{center}
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
+
+
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \begin{frame}[c]