[The following paragraphs refer to the original TeX system, which is
obsolete now that the TeXbook has been published.  New users should use
TeX rather than TeX78.]

TEX is a new document compiler developed by D. E. Knuth.  The monitor
knows about TEX, so you can say "tex foo" and TEX will process the file
FOO.TEX on your area.  Simply saying "tex" will repeat your most recent
tex command.  You can also use αXGO from E.  Of course, you can bypass
Snail by saying "r tex" to the monitor.  TEX will then prompt you with an
asterisk, to which you'll probably want to say "\input foo".  Snail also
allows you to pass parameters:  "tex foo(\bar baz \par)" actually means
"r tex<cr>\bar baz\par\input foo.tex" to TEX.  The switches also remain in
your tmpcor file, so just saying "tex" will rerun with the same file and
switches as last time.

Whenever you \input <file>, TEX reads in <file>.TEX on your area, or if
that file doesn't exist, TEX will try <file>.TEX[TEX,SYS] (but if <file>
has an explicit extension, TEX will use it).  Your output will be on
<file>.PRE and it can be spooled with "dover <file>". When TEX stops, it
puts this spooling command into the line editor, so you merely need to hit
<CR> to get your output spooled. If you don't want to print the output,
<clear> or <call> will remove the unwanted command from your line editor.

When TEX catches an error in your input file, it will stop and tell you
about it.  You are then allowed to tell TEX to pretend that some text that
you enter from your terminal actually was in your file (see the manual for
a complete description of how TEX reports errors, and how you can tell it
to insert or delete text). The idea is that this may enable you to recover
from what might otherwise have been a fatal error.  Thus, TEX continues to
process your input, rather than having to start all over again from the
beginning after you change your file.  This will give you a chance to
catch more errors per run. It is important to note that TEX does not
actually make any change in your input file.  Rather, it makes a file
(ERRORS.TMP in your aliased directory) that contains a transcript of your
entire dialog.  After you are through TEXing, if you have used the
interactive error correction facility, you should go back and edit your
input file, referring to ERRORS.TMP to see what corrections are required.

If you want to TEX somebody else's file, try "tex foo[prj,prg]".  If you
get prompted by an asterisk, try "\par\vfill\end".  The output file will
be put on your current alias.

The original version of TEX produced XGP output. You can still run that
old reliable program by saying "r xgptex". In this case the way to list
the .XGP output file that you get is "xs <file>/head/ntn=33"; omit "/head"
if you don't want the fine print atop each page telling you the date and
time of spooling.  One of the main uses of xgptex these days is to get
output on your datadisc screen in the following way: "r xgpsyn;<file>";
when xgpsyn asks you for a page number, first type "c" and then hit
carriage-returns repeatedly to get successive half-pages displayed on your
screen.

Important:  This version of TEX has thirteen font files preloaded, so any
additional fonts should be assigned font codes other than "@adfgjlnquxz?".
The thirteen standard fonts are defined in file basic.tex[tex,sys].

If you restrict yourself to these thirteen fonts, you can get output
magnified by a factor of 1.0, 1.1, 1.2, 1.3, 1.5, 2.0, or 3.0, since
magnified versions of all these fonts exist on the Dover. Read the
discussion of magnification on ERRATA.TXT[TEX,DEK]/9p for details. One
says e.g. "\input basic \magnify{2000}" to get double magnification.

If you use other fonts, TEX needs the font metric information that appears
on file <fontname>.tfm[tex,sys] (if the fontname has no extension) or on
file <fontname>.tfm[prj,prg] (if the fontname has extension [prj,prg]).
Xerox font names more than six characters long are converted to six-letter
names by retaining the first three and last three characters; for example,
"timesroman" is equivalent to "timman". To get e.g. 10-point timesroman,
the proper TEX incantation is "\font A=timesroman at 10truebp". It turns
out that Xerox fonts have a strange idea of point size so that their
10-point fonts look like a traditional printer's 11-point fonts. Thus,
10-point timesroman will go well with the normal TEX math fonts only when
the latter are magnified by 1.1; say "\input tbasic" to get a version of
"basic.tex" that gives you timesroman text and normal TEX math, magnified
by 1.1. There is also a Helvetica version, obtainable by "\input hbasic".
Exception: A few Xerox fonts are "unscalable"; they are called e.g.
"cream10b" instead of "creamb at 10truebp".

The user manual is A. I. Memo No. 317 ( = CS Report No. 675), reprinted in
the book TeX and METAFONT.  There's no on-line or line-printer version.

The SAIL program contains extensive documentation about the implementation;
it's not merely "commented code". See file TEXSYS.SAI[TEX,DEK] and the
files it references.

Several special versions of TEX exist that have preloaded fonts.  These
include ARKTEX (maintained by Arthur Keller, preloads fonts in
TEXPRE.TEX[TEX,SYS]) and MAXTEX (maintained by Max Diaz, preloads fonts in
KERMAC.TEX[TEX,SYS]).  These preloaded versions are maintained for quick
use of complex macro packages permitting use of many fonts.  ARKTEX is
intended to be used with many macro packages by having the macro package
specify "\input texpre" instead of specifying fonts.  The font letter
assignments in ARKTEX are as standardized by Donald Knuth.  The fonts in
MAXTEX are different.  READ ARKTEX and READ MAXTEX for more details.

This HELP information is on file TEX[3,2].