What is the minimum TeX one can use to put together a mathematical document?

Being a mathematician, I use LaTeX a lot for writing. However, I am interested (mildly) in working with TeX instead, even if only for keeping my own notes. What is the minimum amount of TeX do I need to know to produce reasonable documents with mathematical content? I'm not interested in the finer points of compositing and typefaces and so on, so I may be barking up the wrong tree here.

Also (and this is a stretch) what about diagrams in TeX? Usually I use xymatrix in LaTeX, is there an easy way to do simple diagrams in TeX?

Edit: The answers to the second question are good, but what about the first? Shall I go back a step and ask:

What is the minimum amount of TeX do I need to know to produce reasonable documents?

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I have experience creating stand alone graphics using various TeX-based systems, so I feel that I can answer your second question well. But I have never done a large paper entirely in TeX, so I don't have an answer for your first. Perhaps you should spin off one of your questions into a separate thread since they draw from substantially different areas of expertise? – Sharpie Aug 10 '10 at 5:46
You already got a few answers but I felt I had to add this. Is there really any reason why you would prefer to use TeX over LaTeX to prepare a document? I don't see why you would want to do so, as LaTeX is built on top of TeX, you don't loose anything but gain the support from a lot of available LaTeX packages. – Juan A. Navarro Aug 10 '10 at 11:19
@Juan: LaTeX is also a very opinionated layer-- it forces a lot of design decisions that take some effort to undo if you don't like them. With plain TeX you get to start from scratch which can be more efficient in certain situations. – Sharpie Aug 12 '10 at 7:44
@Sharpie, that sounds fair, use TeX if you want to be a document designer rather than (or in addition to) a content writer. I still think you can stay with LaTeX and do some design (e.g. titlesec, memoir), but of course the situation is not optimal. – Juan A. Navarro Aug 12 '10 at 8:59

For graphics, TikZ supports TeX, LaTeX and ConTeXt. The beautifully illustrated manual starts off with several tutorials that show how to set TikZ up for use with TeX, LaTeX or ConTeXt. After the environment has been set up, the syntax used to draw pictures is consistent across all three systems.

MetaPost is another vector drawing language that grew out of MetaFont and inspired much of the syntax used by TikZ. Hans Hagen, the creator of ConTeXt, has done a lot of work on MetaPost and has produced a very fine manual detailing the system and his MetaFun extensions. The University of Berkeley has an example that shows how to use MetaPost from plain TeX or AMSTeX.

LuaTeX has MetaPost support baked in thanks to MPLib. A plain-TeX example for using MetaPost code inside LuaTeX can be found here.

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Do you know if there is any support for using inline Metapost in Lualatex the way there is for Context? – Charles Stewart Aug 10 '10 at 13:04
Yes. The plain-TeX example I linked to uses the luamplib package which provides the interface and is part of the LuaTeX distribution. – Sharpie Aug 10 '10 at 18:10

On the first question you should be more elaborate. At the most minimum level, the only TeX command you need to know is \end. You should explain what you want to do, reasonable documents on its own is just too vague to give better answers.

On the subject of learning tex, see the excellent (and nowadays free) book TeX by Topic by Victor Eijkhout.

For a short introduction to (plain) TeX, try A Gentle Introduction to TeX by Michael Doob. It is quite old and the part about running TeX and editing is somewhat obsolete, but it covers enough of the plain functionality to get started, and it very easy to follow.

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I'm only looking for enough to encode private notes, with only as much functionality one would get from wordpad, say, but with the typesetting of TeX and the maths capabilities. – David Roberts Aug 11 '10 at 23:22
I elaborated the answer a bit – Taco Hoekwater Aug 12 '10 at 4:53
I think \bye is more useful than \end. :) – TH. Sep 8 '10 at 23:15

I use plain ol' TeX all the time when I want to do something fast. Sometimes from the command prompt. As has been pointed out, the minimal command is \bye. e.g.

$e^{i\pi} + 1 = 0$
\bye


So, the answer to your first question is: you need to know commands in TeX's math mode (mostly the same as LaTeX) and the command \bye . You should be able to make all the notes you need with that.

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bev: I edited your post to conform to markdown syntax (to display the code excerpt as code and prevent \bye from being interpreted as section heading) – Willie Wong Nov 20 '10 at 12:16
@ Willie - thanks. I wondered about that. Now I just have to figure out how to use 'markdown syntax'. Oh well, learn or die is my motto :-) – bev Nov 21 '10 at 0:16

AMSTeX works with plain TeX, adding features for mathematics. It also provides simple macros for (commutative) diagrams: \CD ... \endCD.

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If you're using AmsTeX, I've heard the book The Joy of TeX by Michael Spivak (the same) is an excellent and enjoyable one well worth reading. – ShreevatsaR Aug 10 '10 at 2:56

You can use plain TeX for mathematics. (My PhD thesis, written two decades ago, was typeset in plain TeX with additional macros.) Of course, you may have to provide a number of additional macros if you want cross-referencing,...

As for diagrams, XY-pic (which is what I think you mean by xymatrix) works just fine in plain TeX; although I have not used it in plain TeX in years.

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