--- a/slides/slides02.tex	Tue Sep 26 14:38:45 2017 +0100
+++ b/slides/slides02.tex	Wed Sep 27 14:46:20 2017 +0100
@@ -223,6 +223,52 @@
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \begin{frame}[c]
+\frametitle{\begin{tabular}{c}The Meaning of a\\[-2mm] 
+  Regular Expression\end{tabular}}
+
+\begin{textblock}{15}(1,4)
+ \begin{tabular}{rcl}
+ \bl{$L(\ZERO)$}  & \bl{$\dn$} & \bl{$\{\}$}\\
+ \bl{$L(\ONE)$}     & \bl{$\dn$} & \bl{$\{[]\}$}\\
+ \bl{$L(c)$}            & \bl{$\dn$} & \bl{$\{[c]\}$}\\
+ \bl{$L(r_1 + r_2)$}    & \bl{$\dn$} & \bl{$L(r_1) \cup L(r_2)$}\\
+ \bl{$L(r_1 \cdot r_2)$} & \bl{$\dn$} & \bl{$\{ s_1 \,@\, s_2 \;|\; s_1 \in L(r_1) \wedge s_2 \in L(r_2) \}$}\\
+ \bl{$L(r^*)$}           & \bl{$\dn$} & \bl{$(L(r))\star \quad\dn \bigcup_{0 \le n} L(r)^n$}\\
+  \end{tabular}
+\end{textblock}
+
+\begin{textblock}{6}(9,12)\small
+\bl{$L$} is a function from regular expressions to 
+sets of strings\\
+\bl{$L$ : Rexp $\Rightarrow$ Set$[$String$]$}
+\end{textblock}
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[c]
+\frametitle{\begin{tabular}{c}The Specification\\ of Matching\end{tabular}}
+
+\begin{bubble}[10cm]
+\large
+A regular expression \bl{$r$} matches a string~\bl{$s$} 
+provided
+
+\begin{center}
+\bl{$s \in L(r)$}\\ 
+\end{center}
+\end{bubble}\bigskip\bigskip
+
+\ldots and the point of the this lecture is 
+to decide this problem as fast as possible 
+(unlike Python, Ruby, Java etc)
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[c]
 \frametitle{Semantic Derivative}
 
 \begin{itemize}
@@ -283,42 +329,6 @@
 \end{frame}
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
 
-
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-\begin{frame}[c]
-\frametitle{\begin{tabular}{c}The Meaning of a\\[-2mm] Regular Expression\end{tabular}}
-
-\begin{textblock}{15}(1,4)
- \begin{tabular}{@ {}rcl}
- \bl{$L(\ZERO)$}     & \bl{$\dn$} & \bl{$\{\}$}\\
- \bl{$L(\ONE)$}        & \bl{$\dn$} & \bl{$\{[]\}$}\\
- \bl{$L(c)$}               & \bl{$\dn$} & \bl{$\{[c]\}$}\\
- \bl{$L(r_1 + r_2)$}       & \bl{$\dn$} & \bl{$L(r_1) \cup L(r_2)$}\\
- \bl{$L(r_1 \cdot r_2)$}   & \bl{$\dn$} & \bl{$L(r_1) \,@\, L(r_2)$}\\
- \bl{$L(r^*)$}             & \bl{$\dn$} & \bl{$(L(r))\star$}\\
- \end{tabular}
-\end{textblock}
-
-\begin{textblock}{6}(9,12)\small
-\bl{$L$} is a function from regular expressions to 
-sets of strings\\
-\bl{$L$ : Rexp $\Rightarrow$ Set$[$String$]$}
-\end{textblock}
-
-\end{frame}
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
-
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
-\begin{frame}[c]
-
-\large
-\begin{center}
-What is \bl{$L(a^*)$}?
-\end{center}  
-  
-\end{frame}
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
-
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \begin{frame}[c]
 \frametitle{\begin{tabular}{c}