
diff -r 93bf3182cf71 -r 1bdec6a9e03d handouts/ho01.tex
--- a/handouts/ho01.tex	Thu Sep 26 13:06:27 2013 +0100
+++ b/handouts/ho01.tex	Thu Sep 26 13:15:05 2013 +0100
@@ -104,7 +104,18 @@
 $r_2$. We should also write $(r_1 + r_2) + r_3$ which is a regular expression different from $r_1 + (r_2 + r_3)$,
 but in case of $+$ and $\cdot$ we actually do not care and just write $r_1 + r_2 + r_3$, or $r_1 \cdot r_2 \cdot r_3$,
 respectively. The reasons for this will become clear shortly. In the literature you will often find that the choice
-$r_1 + r_2$  is written as $r_1\mid{}r_2$ 
+$r_1 + r_2$  is written as $r_1\mid{}r_2$. In case of $\cdot$ we will even often omit it all together. For example
+the regular expression for email addresses is meant to be of the form
+
+\[
+([\ldots])^+ \cdot @ \cdot ([\ldots])^+ \cdot . \cdot \ldots
+\]
+
+\noindent
+meaning first comes a name (specified by the regular expression $([\ldots])^+$), then an $@$-sign, then
+a domain name (specified by the regular expression $([\ldots])^+$), then a top-level domain.
+
+
 \end{document}
 
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