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{\let\latex\LaTeX
\let\bibtex\BibTeX
\def\Makeindex{{\tt make\-index}}
\def\pagerefs{{\tt page\-refs}}
\def\awk{{\tt awk}}
\centerline{\bf Cross Referencing the Bibliography}
\smallskip
\leftline{\sl Why cross reference?}
\noindent
When you are looking through an article, 
do you wish that
the bibliography contained cross references to the point
in the text where the item was cited? I often do, and in this note 
I explain why I find this useful and include a small set of
\unix\ based tools to accomplish this task quite painlessly
using \latex\ and \bibtex\ (Patashnik, 1985).

Academic and other sources now publish vast amounts of written
material. You can't read it all and you have to make some kind
of judgement as to what you read carefully, what you skim
quickly and what you ignore.  This is especially true in 
academic circles where we are constantly snowed under with journals,
new journals and conferences, as well as books and
departmental reports.

One of the first things I look at when trying to judge the
relevance of an article is its bibliography. I want and expect
it to be work I have already seen or know
about. There are several occasions though, when something
catches your eye about the list of references, and you want to go
immediately to some particular point of the article:

\item{$\bullet$}
        Perhaps the article is a survey or tutorial and you
	want to see how the authors treat your favourite work
	(or your own!);

\item{$\bullet$}
        Perhaps there is an intriguing article cited: a paper
	you have come across in a totally different context
	and is quite unexpected here. Why is it cited?  Or
	more likely, a paper unknown to you. What is it about?

\item{$\bullet$}
        Perhaps you wish to refresh your memory about 
	something -- you have come back to this paper looking for
	specific comments made by the authors concerning some
	other work. Where do they talk about it? 

\noindent
A bibliography including this kind of cross reference would be
extremely useful to its readers. You can probably think of lots
of other examples yourself. Clearly, cross referencing back into
the text in a book or a thesis can be a great help, but I would
also stress the advantages of doing the same thing in
journals accepting long articles and even short reports and 
conference proceedings.  In particular, books which are
collections of articles by several authors and have collected
bibliographies at the back (or elsewhere!) can benefit greatly
from such a scheme.

This cross referencing is quite specific to the citation in question.
You don't have to go hunting through an index for author's names
which may not give you exactly the right places anyway. Instead
you get exactly the information you want: where the reference was
cited. If you forget the authors' names, bibliographies are
often short enough to scan through to get the right item; In any case,
what journals and conference proceedings have indexes? Even some (bad)
books don't have an index.
\smallskip
\leftline{\sl Producing the cross references}
\noindent
No journals or books that I know of have produced such a
bibliography. Nevertheless, it's not hard to do so; I have already
started and I hope others will follow suit. (I'd like to think that the
conference proceedings and technical reports I find myself reading in
the future will do so. Maybe even one day the technical journals\dots)

I am going to spend the remaining few paragraphs talking about a
small program to produce the bibliography in a \latex\
document. The program is very heavily \unix{}\ biased, and was simply
thrown together in a few hours,  but I hope that
the ideas are clear enough. It is not really a very difficult problem.

In addition to using \latex, we make use of two other `standard'
programs: \bibtex\ and \Makeindex. \bibtex\ will of course
come as no surprise. \Makeindex\ is a program written
by Pehong Chen at Berkeley, with help from Leslie Lamport,
and if you are writing a book with \latex, \Makeindex\ is a program you
must consider using.
Unfortunately,
it is, I believe, only written in C and unavailable outside the \unix{}
world. You will need \Makeindex\ to use my particular implementation.
If you don't have it I believe it is on the standard \unix{} tape from
Washington and several archives, including Aston. If you're not on
\unix, I'm afraid you can't use my implementation anyway because it
relies on \awk. 

The suite consists of:
\itemitem{1:} a \latex\ style file;
\itemitem{2:} a preprocessor made from a couple of \awk\ scripts;
\itemitem{3:} \Makeindex;
\itemitem{4:} a postprocessor, in C;
\itemitem{5:} a shell script, \pagerefs, working on 2--4 above.

\noindent\pagerefs\ runs in a manner analogous to \bibtex. 
\bibtex\ must be run first to produce the {\tt .bbl} file,
and then \pagerefs\ to add the page numbers.

The style file, {\tt pagebib}, simply redefines 
|\cite| to write out the page number 
(but not the |\nocite| command -- it
didn't seem appropriate). None of this interferes with the
normal citation methods of \latex.

The style file also defines a command called |\PageBIB|,
which is used to format the references. My current command is
\begintt
\newcommand{\PageBIB}[1]%
{\hspace*{\fill}\hbox{[#1]}}
\endtt
\noindent You can of course redefine it as you please; I flirted with
the idea of putting the page numbers in marginal notes.

Step~2 simply puts the citations into a suitable form for
\Makeindex, which does all the hard work. Step~4 relies
on the fact that the bibliography styles include the bibliographic
key from the database, (not the label!) in the {\tt bibitem} entry
which is how citations are matched up with labels. I don't know if
this is a step \bibtex\ always does but it certainly works for
the ones I have used -- |alpha|, |plain|, \hbox{|abbrv|},
|unsrt| and |acm|.

Finally, of course, you must run \latex\ again, but this is only a 
real cost if the last thing you did to your manuscript was to add or
delete a reference, in which case you will probably run \bibtex\
again anyway. In the whole scheme of resource usage when writing
and producing a book or article, this particular part is really rather
small.
\smallskip
\leftline{\sl The bibliography}
\noindent
{\frenchspacing\parindent0pt\hangindent20pt\hangafter1
Alfread~V. Aho, Brian~W. Kernighan, and Peter~J. Weinberger,
{\awk}: a pattern scanning and processing language, 1978.

\hangindent20pt\hangafter1
Leslie Lamport,
Makeindex: an index processor, 1988.

\hangindent20pt\hangafter1
Oren Patashnik,
{\bibtex}ing, 1985.
}

\rightline{\sl Christopher P. Higgins}

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