
diff -r 4755ad4b457b -r 8890852e18b7 coursework/cw01.tex
--- a/coursework/cw01.tex	Fri Sep 25 20:59:24 2015 +0100
+++ b/coursework/cw01.tex	Mon Sep 28 23:47:34 2015 +0100
@@ -55,13 +55,15 @@
 $L(r^+)$                  & $\dn$ & $\bigcup_{1\le i}. L(r)^i$\\
 $L(r^?)$                  & $\dn$ & $L(r) \cup \{[]\}$\\
 $L(r^{\{n,m\}})$           & $\dn$ & $\bigcup_{n\le i \le m}. L(r)^i$\\
-$L(\sim{}r)$              & $\dn$ & $\mathbb{A} - L(r)$
+$L(\sim{}r)$              & $\dn$ & $\Sigma^* - L(r)$
 \end{tabular}
 \end{center}
 
 \noindent
-whereby in the last clause the set $\mathbb{A}$ stands for the set of
-\emph{all} strings.  So $\sim{}r$ means `all the strings that $r$
+whereby in the last clause the set $\Sigma^*$ stands for the set of
+\emph{all} strings over the alphabet $\Sigma$ (in the implementation the
+alphabet can be just what is represented by, say, the type \pcode{char})).  
+So $\sim{}r$ means `all the strings that $r$
 cannot match'. 
 
 Be careful that your implementation of $nullable$ and $der$ satisfies
@@ -108,6 +110,14 @@
 \end{tabular}
 \end{center}
 
+\noindent
+Remember your definitions have to satisfy the two properties
+
+\begin{itemize}
+\item $nullable(r)$ if and only if $[]\in L(r)$
+\item $L(der\,c\,r)) = Der\,c\,(L(r))$
+\end{itemize}
+
 \subsection*{Question 3 (marked with 1\%)}
 
 Implement the following regular expression for email addresses
@@ -130,7 +140,7 @@
 $\epsilon \cdot r$ & $\mapsto$ & $r$\\ 
 $r + \varnothing$ & $\mapsto$ & $r$\\ 
 $\varnothing + r$ & $\mapsto$ & $r$\\ 
-$r + r$ & $\mapsto$ & $r$ & (added on 12 October)\\ 
+$r + r$ & $\mapsto$ & $r$\\ 
 \end{tabular}
 \end{center}
 




