diff -r 29fc780ca130 -r fa7f7144f2bb cws/main_cw03.tex
--- a/cws/main_cw03.tex	Tue Dec 07 01:35:00 2021 +0000
+++ b/cws/main_cw03.tex	Tue Dec 07 23:17:51 2021 +0000
@@ -362,10 +362,23 @@
 \end{tabular}
 \end{center}
 
-  The last case is as follows: first apply $simp$ to all regular expressions
-  $r_1,.. ,r_n$; then flatten the resulting list using \texttt{flts};
-  finally remove all duplicates in this list (this can be done in Scala
-  using the function \texttt{\_.distinct}).
+The last case is as follows: first apply $simp$ to all regular
+expressions $r_1,.. ,r_n$; then flatten the resulting list using
+\texttt{flts}; finally remove all duplicates in this list (this can be
+done in Scala using the function
+\texttt{\_.distinct}). \textcolor{red}{When you perform these
+  operations, you end up with three cases, namely where the list is
+  empty, contains a single element and ``otherwise''. These cases
+  should be processed as follows}
+\begin{center}
+\textcolor{red}{\begin{tabular}{l@{\hspace{4mm}}c@{\hspace{4mm}}ll}
+$\sum\;[]$ & $\mapsto$ & $\ZERO$\\ 
+$\sum\;[r]$ & $\mapsto$ & $r$\\ 
+$\sum\;rs$ & $\mapsto$ & $\sum\;rs$ & ``otherwise''\\ 
+\end{tabular}}
+\end{center}
+
+  
 
   For example the regular expression
   \[(r_1 + \ZERO) \cdot \ONE + ((\ONE + r_2) + r_3) \cdot (r_4 \cdot \ZERO)\]