--- a/slides/slides04.tex	Sat Oct 08 16:44:11 2016 +0100
+++ b/slides/slides04.tex	Thu Oct 13 12:55:42 2016 +0100
@@ -929,6 +929,26 @@
 
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \begin{frame}[c]
+
+  Normally we would have
+
+  \begin{center}
+  \bl{$(\ZERO \cdot (b \cdot c)) + ((\ZERO \cdot c) + \ONE)$}
+  \end{center}
+
+  and answer
+
+  \begin{center}
+  \bl{$Right(Right(Empty))$}
+  \end{center}\bigskip
+
+  But now we simplify to \bl{$\ONE$} and produce \bl{$Empty$}.
+
+\end{frame}
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%  
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{frame}[c]
 \frametitle{Rectification}
 
 \def\arraystretch{1.05}