|Many of these books may be out of print now, so you may have to hunt
|through Computer Science Libraries and UNIX programmer's secret caches.

    Troff User's Manual, by Ossanna and Kernighan, is available for
|	anonymous ftp as ftp://netlib.att.com/netlib/att/cs/cstr/.
|	The above URL may no longer be in existance, but apparently,
|	it's now available at http://www.kohala.com/~rstevens/troff/cstr54.ps
|	Also available is Kernighan's raw troff tutorial at:
|	http://www.kohala.com/~rstevens/troff/v7man/trofftut/trofftut.ps

    Document Formatting and Typesetting on the UNIX System,
	2 volumes, Nerain Gehani, Silicon Press, ISBN 0-9615336-2-5.
	A very good general reference; covers troff, the preprocessors,
	and most of the popular macro packages.

    Typesetting Tables on the UNIX System, Henry McGilton, Mary McNabb.
	Trilithon Press, ISBN 0-9626289-0-5.  A very good, very complete
	reference and tutorial on TBL.

    Unix Text Processing, Dale Dougherty & Tim O'Reilly, Hayden Books,
	ISBN 0-672-46291-5.  A good discussion not just of troff (ms & mm),
	tbl, eqn, and pic, but also vi and ex, sed, and awk.

    Troff typesetting for Unix Systems, Sandra L. Emerson & Karen Paulsell
	(kjp@well?) Prentice-Hall, 0-13-930959-4.  This is a good book
	for people wishing to write raw troff (as in rolling your own
	macros)

    troff-Programmierung: proffessionelle Textverarbeitung und
        Schriftsatz unter UNIX, Claus Schirmer, Hanser Verlag 1990,
        ISBN 3-446-15649-6.  Reportedly a superb book on troff
	programming.  Ie: a ms-like macro package is built in a
	step-by-step way.  Don't know if there's non-German language
	version.

    The UNIX Text Processing System, Kaare Christian, Wiley, 1987.
	Is especially good on REFER, the best chapter on REFER
	available.  [This book now appears to be out of print.]

    Text processing and typesetting with UNIX, D.W. Barron and Mike Rees,
	Addison-Wesley, 1987.