--- a/slides/slides06.tex	Sat Nov 04 18:28:09 2023 +0000
+++ b/slides/slides06.tex	Sat Nov 11 10:08:33 2023 +0000
@@ -79,6 +79,24 @@
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[t]
+\frametitle{Palindromes}
+
+A grammar for palindromes over the alphabet~\bl{$\{a,b\}$}:
+
+\only<1>{%
+\bl{\begin{plstx}[margin=1cm]
+: \meta{S} ::=  a\cdot \meta{S}\cdot a | b\cdot \meta{S}\cdot b | a | b | \epsilon\\
+\end{plstx}}}
+
+%\small
+%Can you find the grammar rules for matched parentheses?
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \begin{frame}[c]
 \frametitle{Parser Combinators}
 
@@ -103,6 +121,17 @@
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \begin{frame}[c]
+\frametitle{Abstract Parser Class}
+
+\small
+\lstinputlisting[language=Scala,xleftmargin=1mm]
+ {../progs/app7.scala}
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%  
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[c]
 
 Atomic parsers, for example, number tokens