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+<title> Commutative Diagrams in TeX</title>
+
+<h1 align="center">Commutative Diagrams in TeX </h1>
+
+<h3 align="center">Paul Taylor </h3>
+
+<h3 align="center">September 1992 </h3>
+
+
+
+
+<div class="p"><!----></div>
+
+<div class="p"><!----></div>
+
+<div class="p"><!----></div>
+
+<div class="p"><!----></div>
+
+<div class="p"><!----></div>
+
+<div class="p"><!----></div>
+
+<div class="p"><!----></div>
+
+<div class="p"><!----></div>
+
+<div class="p"><!----></div>
+
+<div class="p"><!----></div>
+
+<div class="p"><!----></div>
+
+<div class="p"><!----></div>
+
+<div class="p"><!----></div>
+
+
+<div class="p"><!----></div>
+
+
+
+
+
+
+<div class="p"><!----></div>
+
+<div class="p"><!----></div>
+
+
+
+<div class="p"><!----></div>
+
+
+
+<div class="p"><!----></div>
+
+
+<div class="p"><!----></div>
+
+
+
+<div class="p"><!----></div>
+
+
+
+
+
+
+<div class="p"><!----></div>
+
+
+<div class="p"><!----></div>
+
+
+<h2>Message sent to registered users in September 1992</h2>
+
+<div class="p"><!----></div>
+This message brings news of the development of my <span class="roman">T</span><sub><span class="roman">E</span></sub><span class="roman">X</span>&nbsp;package for
+drawing "commutative" diagrams, which is now widely used in the
+category theory and theoretical computer science communities. It is
+being sent directly to all of the users I know of (who have requested
+it by electronic mail or FTP from me, or asked questions about it),
+but as I know the package has been passed on, I would be grateful if
+you would <em>copy this message to anyone to whom you have given
+ the package itself.</em>
+
+<div class="p"><!----></div>
+The package was originally advertised on the "types" and
+"categories" electronic mailing lists in July 1990. In the following
+eighteen months some fixing of bugs took place, but there was little
+substantial change.
+
+<div class="p"><!----></div>
+Since April 1992, I have re-written most of the code, largely with a
+view to improving the geometrical layout of the diagrams. Before
+completing this work and calling it version 4, I would like some
+feedback from users.
+
+<div class="p"><!----></div>
+One of the areas which I have neglected in the past (largely because
+<span class="roman">T</span><sub><span class="roman">E</span></sub><span class="roman">X</span>&nbsp;makes it so difficult) is diagonal arrows. The code for drawing
+these using <span class="roman">L</span><sup><span class="roman">A</span></sup><span class="roman">T</span><sub><span class="roman">E</span></sub><span class="roman">X</span>&nbsp;line segments has been re-written: now the closest
+available slope is chosen automatically and the commands have names
+similar to the horizontals and verticals.
+
+<div class="p"><!----></div>
+However to do a better job of diagonals (and in future to support
+curved lines) some extension to <span class="roman">T</span><sub><span class="roman">E</span></sub><span class="roman">X</span>&nbsp;is needed. Being extensions they
+are necessarily not standard. Three possibilities are:
+
+<ul>
+<li> additional fonts (as, for example, used by Spivak's Lamstex).
+ However my experience of design-size fonts and linear logic symbols
+ suggests that for users without expert knowledge or control of their
+ local <span class="roman">T</span><sub><span class="roman">E</span></sub><span class="roman">X</span>&nbsp;systems this is more trouble than it's worth.
+<div class="p"><!----></div>
+</li>
+
+<li> PostScript is, I believe, now almost universally used as the
+ language in which <span class="roman">T</span><sub><span class="roman">E</span></sub><span class="roman">X</span>&nbsp;documents are sent to a printer. PS commands
+ can be embedded in DVI files and incorporated in the PS translation
+ without extra system or user files or any user intervention. This is
+ to some extent dependent on which DVI<font face="symbol">®</font
+>PS translator is used. In
+ the new version this is exploited in an option to implement
+ diagonals by rotating horizontals, which works with Tomas Rokicki's
+ "dvips".
+<div class="p"><!----></div>
+</li>
+
+<li> TPIC is a graphics extension of <span class="roman">T</span><sub><span class="roman">E</span></sub><span class="roman">X</span>&nbsp;which uses a simpler set
+ of embedded commands. These can be used to draw diagonal lines and
+ curves but not to perform rotations; they are, however, understood
+ by Vojta's "xdvi" as well. Another option in the new version uses
+ these to draw diagonal lines.
+<div class="p"><!----></div>
+</li>
+</ul>
+Besides diagonals, the code for adjusting horizontal and vertical
+arrows has been completely rewritten and does a much better job of the
+geometry. Many of the problems with alignment, positioning and gaps
+have been fixed automatically, and greater control is given to the
+user to adjust those which cannot be. There are also several new
+options for the placement of the finished diagram on the page.
+
+<div class="p"><!----></div>
+Arrow commands are now declared in a much simpler way. The declaration
+
+<pre>
+&nbsp;\newarrow{CrossedInto}{hook}-+-&#62;
+
+</pre>
+is now all that is needed to define the example <tt>\rCrossedInto</tt>
+in the manual, along with the corresponding left, down, up and
+diagonal commands. Another option makes a consistent selection of
+arrowheads for all arrows, from a choice of vee, LaTeX, curlyvee,
+triangle and blacktriangle.
+
+<div class="p"><!----></div>
+So much for selling you the new version. The reason for mailing you
+and asking for comments before completing what I intend to do for
+version 4 is that I want to get feedback on the following questions:
+
+<div class="p"><!----></div>
+
+<ul>
+<li> Can you use FTP (file transfer protocol)? This is the easiest
+ method of distribution for me and for you, and there is now a huge
+ volume of public domain software available by this method. My
+ archive is called <tt>ftp.dcs.qmw.ac.uk</tt>
+ and the diagrams package is in the directory /pub/tex/contrib/pt/diagrams.
+ Please try to fetch the new version and manual by this method.
+<div class="p"><!----></div>
+</li>
+
+<li> If you can't use FTP, and your electronic mail passes via
+ non-ASCII machines (particularly BITNET), what characters tend to
+ get corrupted? The new version uses a restricted character set to
+ avoid this problem.
+<div class="p"><!----></div>
+</li>
+
+<li> Do you have available for printing final copy a printer which
+ understands Adobe PostScript, for example an Apple or Sun
+ laserwriter? Who is the author of the DVI-&#62; PS translation program
+ you use? Please fetch the new version, try the PostScript option and
+ tell me if you have any difficulty printing. (You may have to change
+ the <tt>\verbatim@ps@special</tt> macro if you don't use Rokicki's
+ dvips: if so, please send me details.) You can preview with a PS
+ previewer such as PageView under OpenWindows or
+ GhostView/GhostScript under Xwindows.
+<div class="p"><!----></div>
+</li>
+
+<li> Do your DVI translators and previewers understand TPIC
+ <tt>\special</tt>s (as used in eepic.sty)? Please try the TPIC
+ option. I would like to know whether it is worth putting effort into
+ PostScript, TPIC or some other method.
+<div class="p"><!----></div>
+</li>
+
+<li> Have you defined your own arrow commands using
+ <tt>\HorizontalMap</tt>, <tt>\VerticalMap</tt> or <tt>\DiagonalMap</tt>?
+ Please use "grep alMap *.tex *.sty" or some similar command to
+ find out, and tell me if you have used any components other than
+ those in the source of version&nbsp;3. It is in your interests to do
+ this, because <tt>\newarrow</tt> defines arrow commands in a
+ different way.
+<div class="p"><!----></div>
+</li>
+
+<li> Please tell me if you have any difficulty adapting to the new
+ version, or any general comments about doing so which might be of
+ benefit to other users.
+<div class="p"><!----></div>
+</li>
+
+<li> Other comments: have you used other packages for drawing
+ diagrams? Do you have applications for my package other than the
+ categorical diagrams for which it was designed? What do you see as
+ the major limitations of the package? What persuaded you to use it,
+ or not to use it?
+<div class="p"><!----></div>
+</li>
+</ul>
+
+<div class="p"><!----></div>