--- a/handouts/ho04.tex	Mon Oct 13 08:43:51 2014 +0100
+++ b/handouts/ho04.tex	Thu Oct 16 11:59:39 2014 +0100
@@ -1,22 +1,39 @@
 \documentclass{article}
 \usepackage{../style}
 \usepackage{../langs}
-
-\usepackage{xcolor}
-\usepackage{tikz}
-\usetikzlibrary{arrows}
-\usetikzlibrary{automata}
-\usetikzlibrary{shapes}
-\usetikzlibrary{shadows}
-\usetikzlibrary{positioning}
-\usetikzlibrary{calc}
-\usetikzlibrary{fit}
-\usetikzlibrary{backgrounds}
+\usepackage{../graphics}
 
 
 \begin{document}
 
-\section*{Handout 4}
+\section*{Handout 4 (Sulzmann \& Lu Algorithm)}
+
+So far our algorithm based on derivatives was only able to say
+yes or no depending on whether a string was matched by regular
+expression or not. Often a more interesting question is to
+find out \emph{how} a regular expression matched a string?
+Answering this question will help us with the problem we are
+after, namely tokenising an input string, that is splitting it
+up into its ``word'' components. The algorithm we will be
+looking at was designed by Sulzmann \& Lu in a rather recent
+paper. A link to it is provided at KEATS, in case you are
+interested.\footnote{In my humble opinion this is an
+interesting instance of the research literature: it contains a
+very neat idea, but its presentation is rather sloppy.
+Students and I found several rather annoying typos in their
+examples and definitions.}
+
+In order to give an answer for how a regular expression matched
+a string, Sulzmann and Lu introduce \emph{values}. A value 
+will be the output of the algorithm whenever the regular 
+expression matches the string. If not an error will be raised.
+Since the first phase of the algorithm is identical to the
+derivative based matcher from the first coursework, the 
+function $nullable$ will be used to decide whether as string
+is matched by a regular expression.
+
+
+
 
 Algorithm by Sulzmann, Lexing