IncTeX is an incremental version of TeX. It is derived from
Common TeX 2.9 by Pat Monardo.  IncTeX analyzes the document
(LaTeX or plain TeX or or other type of style) and reformats the pages
which have changed.  There is some overhead and limit to
its ability to know when it can skip reformatting a page.
It checkpoints the state and input at page breaks so it can
reformat individual pages.  It finds the page where the first
change occurs and restarts formatting.  It parses the formatter state
and skips reformatting when it can guarantee that the formatter
has returned to a state on a later page that is equivalent to
the previous time it was formatting.  A document change that
permanently changes the formatter state (like changing the sections)
prevents this.

IncTeX traces the entire set of include's in the input path.
It is as sophisticated as "make" in understanding where and
how to reposition itself in the input files.
The .aux file is always read at the beginning of LaTeX documents, so
anything that changes the aux file (like changing paper citations) has
the unfortunate side effect of requiring formatting to restart at
the first page.  IncTeX usually reformats from page 1 the first TWO
times it is run on a LaTeX file, because the .aux file
has new contents on the second pass.

IncTeX is run like normal TeX or LaTeX, with all of the same flags.
Type "itex <file>" or "ilatex <file>".
"ilatex myarticle" runs IncTeX on a LaTeX file called myarticle.tex.
IncTeX also has these special flags:

  -v	: Reformat the whole document.
  -j N	: Save checkpoints every N pages (jump N).
	  This is to reduce storage use if you have a lot of pages.
  -q	: Disable quiescence checking.  IncTeX will not check the
	  formatter state at the end of each page to see if reformatting
	  can be skipped.  This is to reduce overhead if you know
	  you will have to reformat from the first change through the end.
  -i	: Force incremental mode.  IncTeX skips reformatting and restarts
	  at the next page where there is a change.
  	  However, it tries to estimate whether reformatting the intervening
	  pages would be faster than loading a checkpoint and decompressing
	  it using page formatting and checkpointing timing.  System load
	  or pausing IncTeX with a debugger throws this logic off and
	  causes it to reformat erroneously.  This flag turns off this
	  feature and it will always skip formatting and load a checkpoint.
  -b	: Run in batch mode (turn off all incremental operation).
	  IncTeX will run just like CommonTeX 2.9.

(Your TEXFORMATS environment variable so it picks up
the .fmt files for IncTeX on your system if they have not been put
in the normal TeX directory)

You should have a megabyte or so of free disk space to run IncTeX.
The storage overhead for IncTeX consists of copies of the (writable)
input files and formatter checkpointing information.
If a file is a style file or read-only or
write-only it does not bother to save it; inctex will just
save the file timestamp so it knows if it is changed.
Checkpoint sizes depend on the page complexity and the formatter state, and
vary from 7K to 35K per page.  These files are stored in a local
subdirectory called INC.  One technique you may want to use is
to create a directory on a volume which has more free space,
and make a symbolic link called INC to that directory.
Since checkpoints are large, when you no longer want to use IncTeX
on a document, you should delete the INC directory and free up the space.

IncTeX was written as a master's thesis project.  This version
has been updated from the one which is described.  Instead of saving
each page as a separate dvi file, the new pages are put in one file
and combined with the previous pages to make the new version.  This
cuts down the number of UNIX file opens and speeds it up.
The thesis is available from the Publications Office, 571 Evans Hall,
Univ. of California at Berkeley, Berkeley, CA 94720, USA,
Tech Report #614, "IncTeX: An Incremental Document Processing System",
by Michael A Harrison and Derluen Pan.

The following information may help you if are getting strange formatting
errors.  When LaTeX is aborted, the .aux file can be left in a garbled or
incomplete state which causes error messages to be printed and
future formatting to fail or be incorrect.  If this situation
happens with IncTeX, you should delete the .aux file and reformat
with the -v flag.  Try this if execution of IncTeX failed (it core dumped)
and you don't understand why future runs have strange errors.