ACL2 works on Unix/Linux, Macintosh, and some Windows operating systems (at least including Windows 98, Windows 2000, and Windows XP). It can be built on top of any of the following Common Lisps:
Gnu Common Lisp (GCL) has probably been the most commonly-used platform for ACL2, certainly among non-commercial Lisps. IMPORTANT: Here we are referring to the non-ANSI version (sometimes called the "CLtL1 version") of GCL. It is probably impossible to build ACL2 with ANSI GCL as of December 2005, but recent GCL advances suggest that this may be possible soon.
Debian package. You do not need to fetch GCL if you download the binary Debian package for ACL2. Thanks to Camm Maguire for maintaining this package.
GCL may be fetched from http://www.gnu.org/software/gcl/.
If that site goes down, you may be able to find useful information from the GCL Temporary Distribution Site.
GCL maintainer Camm Maguire suggests the following, in order of preference
(most to least):
You may obtain recent CVS versions by executing the following commands if you have CVS installed on your system, which will retrieve the latest development/unstable cvs sources by default.
export CVS_RSH=ssh [or, if using csh: setenv CVS_RSH ssh] cvs -d:ext:anoncvs@subversions.gnu.org:/cvsroot/gcl co gclIf you happen to know a particular version of GCL that you wish to obtain, perhaps by following GCL mailing lists, you can replace the commands above by commands such as the following.
export CVS_RSH=ssh [or, if using csh: setenv CVS_RSH ssh] cvs -d:ext:anoncvs@subversions.gnu.org:/cvsroot/gcl co -r Version_x_y_z -d gcl-x.y.z gcl
Macintosh. Robert Krug has provided instructions for building GCL on Mac OS X, which we include here (very slightly modified, in part with help from Camm Maguire) in case others find them helpful.
The normal build process for GCL on Mac OS X assumes that
you have installed fink on your Mac. (If you do not know
what this is, don't worry; you probably don't have it or
want it.) Here we give instructions that have worked for
building GCL on OS X without fink.
A. Obtain recent sources (there is a problem, e.g., with
gcl-2.6.7). For example, you can do the following:
export CVSROOT=:pserver:anonymous@cvs.sv.gnu.org:/sources/gcl
cvs -z9 -q co -d gcl-2.6.8pre -r Version_2_6_8pre gcl
At some point you may be able to obtain GCL from
ftp://ftp.gnu/org/, cd gnu, cd gcl, get
gcl-2.6.8.tar.gz, tar xfz gcl-2.6.8.tar.gz)
B. Make sure that /usr/local/bin is in your PATH; if not, run:
PATH="$PATH:/usr/local/bin"
C. cd <gcl directory>
D. You now need to patch file h/powerpc-macosx.defs (this might not be
necessary starting with GCL 2.6.8):
Replace the line:
LIBS := `echo $(LIBS) | sed -e 's/-lncurses/ /'` /sw/lib/libintl.dylib
With:
LIBS := `echo $(LIBS) | sed -e 's/-lncurses/ /'` /usr/local/lib/libintl.dylib
E. Configure and start to build gcl:
./configure
make
F. Install gcl:
sudo make install
Allegro Common Lisp is probably the most commonly-used commercial platform for
ACL2. You may be able to obtain a trial version from its web site,
http://www.franz.com/.
CMU Common Lisp (sometimes called CMUCL) is a non-commercial Common Lisp
implementation, available from http://www.cons.org/cmucl/.
SBCL (Steel Bank Common Lisp) is a non-commercial Common Lisp
implementation, available from http://sbcl.sourceforge.net/.
CLISP is a non-commercial Common Lisp implementation, available from http://clisp.cons.org/.
OpenMCL, a free Common Lisp implementation that runs on Macintosh OS X, is
available from http://openmcl.clozure.com/.
Lispworks is a commercial Common Lisp available from
http://www.lispworks.com/.
Lispworks note. We initially encountered a problem in getting ACL2 to run under LIspworks 4.2.0. The Lispworks folks provided a patch and suggested that we make the following announcement.
Users with LispWorks4.2.7 should ask us at lisp-support@xanalys.com for the transform-if-node patch. It will be helpful if they quote (Lisp Support Call #11372) when doing so. Also, they must send a bug form generated from their LispWorks image: instructions at http://www.lispworks.com/support/bug-report.html.
/home/jones/acl2/v3-1.
The sources come with a books subdirectory (here
for the latest non-incremental release)
that you may find helpful in your proof development and programming with ACL2.
The following two collections of books are not included with the sources. You
can extract them in the books/ subdirectory of your ACL2
distribution; see the discussion below on certifying
books for information on using them.
For Linux (especially Debian GNU Linux), you can download the Debian package for Linux. Thanks to Camm Maguire for maintaining this package, and for pointing out that as Debian packages are simply ar and tar archives, they can be unpacked on any linux system, and who says: If someone is running Debian, all they want to do is 'apt-get install acl2', doing likewise for any optional add-on package they wish as well, e.g. emacs, infix, etc.
You can fetch the above package for a linux
system other than Debian and unpack it as follows. First, connect to the
directory under which you install ACL2 versions and download the
.deb file there. Then submit these commands (changing
"2.9-7" and "i386" as appropriate).
mkdir acl2_2.9-7 cd acl2_2.9-7 mv ../acl2_2.9-7_i386.deb . ar x acl2_2.9-7_i386.deb tar xvfz data.tar.gzThis will create subdirectory
usr/. Edit
usr/bin/acl2 by replacing "/usr" with the full
pathname for "usr".
Alternatively, you can use the program alien to convert the
.deb file to .rpm format. Of course, with the method
shown above or with alien, you will not have the benefit of
package maintenance.
Jared Davis has kindly been providing, typically soon after an ACL2 release, a Windows installer for ACL2. The download includes a Unix environment, pre-certified standard and workshop books, and a copy of Gnu Emacs.
md5sum and
compare with
acl2-tar-gz-md5sum if you wish to verify the transmission.)
tar xpvfi
acl2.tar", if you have problems with other than Gnu tar. You can see if
you have Gnu tar by running "tar -v".)
cd dirgunzip acl2.tar.gztar xpvf acl2.tarrm acl2.tarhttp://www.cs.utexas.edu/users/moore/acl2/v3-1/distrib/acl2.tar.gz,
and then extract using an appropriate tar utility. For example,
for Windows systems you may be able to download a utility such as
djtarnt.exe to be used as follows:
djtarnt.exe -x acl2.tar.gzWARNING: At least one user experienced CR/LF issues when using WinZIP, but we have received the suggestion that people untarring with that utility should probably turn off smart cr/lf conversion.
For a non-incremental release, you may be able to fetch files individually from
directory (and subdirectories, sub-subdirectories, etc., for example as follows:
http://www.cs.utexas.edu/users/moore/acl2/v3-1/distrib/acl2-sources/.
You will find that the ACL2 distribution
contains many files, subdirectories, sub-subdirectories, etc. We mean
for you to copy over to your local connected directory the entire
structure of files and subdirectories. Thus, when you have completed
extracting from acl2.tar.gz, or fetching all files directly
is done, your local connected directory should have a subdirectory
named acl2-sources under which everything resides.
Now proceed to Creating An Executable Image.
PLEASE NOTE: The available memory for ACL2 is determined by the underlying Common Lisp executable. If you need more memory, refer to your Common Lisp's instructions for building an executable.
-md5sum file
was created using md5sum. We may add additional
links from time to time.
Note that the Debian images may work with other Linux systems as well.
Now proceed to Using ACL2.
cd
acl2-sourcesmake LISP=xxx
By default, if no LISP=xxx is specified,
LISP=gcl is used. On our hosts, gcl is the name of
GNU Common Lisp, which can be obtained as explained above.
This will create executable saved_acl2 in the
acl2-sources directory.
The time taken to carry out this process depends on the host processor but may be only a few minutes for a fast processor. The size of the resulting binary image is dependent on which Lisp was used, but it may be in the vicinity of 17 megabytes.
This make works for the Common Lisps listed in Requirements above on Unix and Linux systems we have
tested. See the file acl2-sources/GNUmakefile for further details.
If this make command does not work for you, please see the
instructions for non-Unix/Linux systems below.
You can now skip to Using ACL2.
See also Building an Executable Image on Some Particular Systems, in case you want to skip directly to the instructions in one of its subtopics.
Otherwise, proceed as follows.
Your Common Lisp should be one of those listed in
Requirements above. Filenames
below should default to the dir/acl2-sources
directory, e.g., for GCL, connect to
dir/acl2-sources before invoking GCL or, after
entering GCL, do (si::chdir
"dir/acl2-sources/").
nsaved_acl2 if it exists.
acl2-sources directory
and submit the following sequence of commands.
; Compile (load "init.lisp") (in-package "ACL2") (compile-acl2)The commands above will compile the ACL2 sources and create compiled object files on your
acl2-sources subdirectory.
acl2-sources subdirectory. In the
fresh Lisp type:
; Initialization, first pass (load "init.lisp") (in-package "ACL2") (load-acl2) (initialize-acl2)This will load the new object files in the Lisp image and bootstrap ACL2 by reading and processing the source files. But the attempt at initialization will end in an error saying that it is impossible to finish because a certain file was compiled during the processing, thus dirtying the image yet again. (If however the attempt ends with an error during compilation of file
TMP1.lisp, see the first troubleshooting tip below.)
acl2-sources subdirectory). Then, in the
fresh Lisp type:
; Initialization, second pass
(load "init.lisp")
(in-package "ACL2")
(save-acl2 (quote (initialize-acl2))
"saved_acl2")
You have now saved an image. Exit Lisp now. Subsequent steps will put the
image in the right place.
osaved_acl2 if it exists.
saved_acl2 and saved_acl2.dxl both exist THEN:
saved_acl2.dxl to osaved_acl2.dxl
saved_acl2 to osaved_acl2
and edit osaved_acl2, changing saved_acl2.dxl
(at end of line) to osaved_acl2.dxl
saved_acl2 exists THEN:
saved_acl2 to osaved_acl2
nsaved_acl2 to saved_acl2.
nsaved_acl2.dxl should exist;
move it to saved_acl2.dxl
saved_acl2 is executable.
ftp://ftp.gnu.org/gnu/gcl/
or as explained above. You
may wish to pick a .zip file from the cvs/
subdirectory (containing pre-releases) that has "mingw32" in the
name.
gclm/bin/gclm.bat that came with
gcl-cvs-20021014-mingw32 from the above ftp site, a separate
window popped up, and with an error. Many ACL2 users prefer running in an
emacs shell buffer. (We obtained emacs for Windows from ftp://ftp.gnu.org/gnu/windows/emacs/21.2/emacs-21.2-fullbin-i386.tar.gz.)
The following modification of gclm.bat seemed to solve the problem
(your pathnames may vary).
@ % do not delete this line % @ECHO off set cwd=%cd% path C:\gcl\gclm\mingw\bin;%PATH% C:\gcl\gclm\lib\gcl-2.6.1\unixport\saved_gcl.exe -dir C:/gcl/gclm/lib/gcl-2.6.1/unixport/ -libdir C:/gcl/gclm/lib/gcl-2.6.1/ -eval "(setq si::*allow-gzipped-file* t)" %1 %2 %3 %4 %5 %6 %7 %8 %9
saved_acl2.exe rather than saved_acl2.
acl2.bat as explained in
http://www.cs.utexas.edu/users/moore/acl2/v3-1/distrib/images/Readme.html.
We hope that the above simply works. If you experience problems, the following hints may help.
TROUBLESHOOTING:
TMP1.lisp. That was easily remedied by starting up a
fresh GCL session and invoking (compile-file "TMP1.lisp") before
proceeding to the next step.
http://www.faculty.idc.ac.il/yishai/reasoning/win-install.htm,
some of which we have tried to incorporate here. A useful point made there is
that when you want to quit ACL2, use :good-bye (or
(good-bye) which works even in raw Lisp). Or you can use
(user::bye) in raw Lisp. The point is: Avoid control-c
control-d, even thought that often works fine in emacs under
Unix/Linux.
PATH variable gcl-dir\gcc\bin, where
gcl-dir is the directory where GCL is installed. To get to the place to
set environment variables, you might be able to go to the control panel, under
system, under advanced. Alternately, you might be able to get there by opening
My Computer and right-clicking to get to Properties,
then selecting the Advanced tab. At one time, when GCL/Windows
was release as Maxima, Pete Manolios suggested adding the system variable
LD_LIBRARY_PATH with the value "maxima-dir\gcc\i386-mingw32msvc\include"; this
may or may not be necessary for your GCL installation (and the path would of
course likely be different).
Building ACL2 on Windows from Scratch
_____________________________________________________________
Note: The disk space requirements are large. Not including
emacs, I had about 275 MB taken up by msys/mingw32/gcl/acl2
during the build process. You can probably use much less
space by removing files after you use them, but I didn't
bother to do that.
Here are the steps I took:
Downloaded emacs 21.3 full distribution and installed
Downloaded msys 1.10.10, installed to c:\acl2
Downloaded mingw 3.1.0-1, installed to c:\acl2\mingw
Downloaded gcl 2.5.3, extracted to c:\acl2\mingw
Downloaded acl2 2.8, extracted to c:\acl2\sources
Compiling gcl:
in msys:
cd /acl2/ming2/gcl-2.5.3
./configure
make
make install
Compiling acl2:
copy "etags.exe" to /mingw/bin. you can find this program
in your emacs folder, under "bin".
in msys:
cd /sources
make
Certifying ACL2 books:
This took 111 minutes on my Athlon 2500+
in msys:
cd /sources
mv nsaved_acl2.gcl.exe saved_acl2.exe
vim books/Makefile-generic, remove "nice" from this line:
ACL2=time nice ../../saved_acl2
make certify-books ACL2=/sources/saved_acl2.exe
We assume you have obtained ACL2 and placed it in directory dir, as
described above for Unix/Linux or other platforms.
(If you downloaded a pre-built ACL2 image, then you may skip this section.)
Connect to subdirectory acl2-sources of dir,
start up your Common Lisp, and compile by executing the following forms.
This sequence of steps need only be performed once.
(load "init.lisp") (in-package "ACL2") (compile-acl2)Now each time you want to use ACL2, you need only execute the following forms after starting up Common Lisp in subdirectory
acl2-sources of
dir.
(load "init.lisp") (in-package "ACL2") (load-acl2) (initialize-acl2)Note. The resulting process includes the ACL2 documentation, and hence will probably be considerably larger (perhaps twice the size) than the result of running an executable image created as described above.
Now proceed to read more about Using ACL2.
acl2-sources may be found in the file all-files.txt
in that directory.
Readme.html; This file
acl2-sources/
LICENSE ; GNU General Public License
GNUmakefile ; For Unix/Linux make.
TAGS ; Handy for looking at source files with emacs
*.lisp ; ACL2 source files
all-files.txt ; List of all files in this directory and subdirectories
books/ ; Examples, potentially useful in others' proofs. See books/Readme.html.
doc/ ; ACL2 documentation in various formats
emacs/ ; Miscellaneous emacs and file utilities, especially emacs-acl2.el
init.lisp; Useful for building the system
interface/
emacs/ ; Support for ACL2 "proof trees". See interface/emacs/README.doc.
infix/ ; ACL2 infix printer by Mike Smith. See interface/infix/README.
saved/ ; Empty directory for backing up copies during make; not important
acl2.tar.gz; gzip'd tar file containing all of acl2-sources/ (see below)
images/ ; Some gzip'd tar'd executables; see images/Readme.html
split/ ; The result of splitting up acl2.tar.gz; see split/Readme.html
The entire acl2.tar.gz is a little more than 6 megabytes, which expands out to nearly
30 megabytes. Additional space is required to build an image, perhaps 30 to 120
megabytes depending on the Lisp, and to certify books.
acl2.tar.gz file in order to build
acl2. That file includes more than just the ACL2 sources proper. It
suffices, for building ACL2, via the instructions above, to fetch only
the acl2-sources/*.lisp files, which take up `only' about
5 megabytes, together with the file
acl2-sources/GNUmakefile.
acl2-sources.
The sources and perhaps an executable image are located on that subdirectory.
However, if you have not saved an image but instead use the directions above
for Running Without Building an Executable Image, skip
to When ACL2 Starts Up below.
The executable image is called acl2-sources/saved_acl2. You can
invoke ACL2 by running that image, e.g.,
mycomputer% dir/acl2-sources/saved_acl2
If on a Unix/Linux system, then to make it easy to invoke ACL2 by typing a
short command, e.g.,
mycomputer% acl2
you may want to install an executable file on your path, e.g.,
/usr/local/bin/acl2, containing the following two lines:
#!/bin/csh -f
dir/acl2-sources/saved_acl2
Note: A carriage return in the file after the last line above is important!
Some hosts then automatically enter the ACL2 ``command loop,'' an ACL2 read-eval-print loop with the prompt:
ACL2 !>Other hosts will leave you in Common Lisp's read-eval-print loop. If yours is one of the latter, evaluate the Common Lisp expression
(ACL2::LP) or simply (LP) if the current
package is "ACL2".
Once in the ACL2 command loop, you can type an ACL2 term, typically followed by ``return'' or ``enter,'' and ACL2 will evaluate the term, print its value, and prompt you for another one. Below are three simple interactions:
ACL2 !>t T ACL2 !>'abc ABC ACL2 !>(+ 2 2) 4
To get out of the ACL2 command loop, type the :q command.
This returns you to the host Common Lisp. We sometimes call this
``raw Lisp.'' You may re-enter the command loop with
(LP) as above.
Note that when you are in raw Lisp you can overwrite or destroy ACL2 by executing inappropriate Common Lisp expressions. All bets are off once you've exited our loop. That said, many users do it. For example, you might exit our loop, activate some debugging or trace features in raw Lisp, and then reenter our loop. While developing proofs or tracking down problems, this is reasonable behavior.
Now you are ready to test your image.
An easy way to test the theorem prover is to type the following term to the ACL2 command loop:
:mini-proveallThis will cause a moderately long sequence of commands to be processed, each of which is first printed out as though you had typed it. Each will print some text, generally a proof of some conjecture. None should fail.
A more elaborate test is to certify the ``books''
that come with the distribution, which is a good idea anyhow; this is our next
topic. On a Unix/Linux system, you can also certify just a small but useful
subset of the books in a few minutes by executing, in directory
dir/acl2-sources:
make certify-books-short
acl2-sources/books. See acl2-sources/books/Readme.html
for information. The general topic of books is discussed thoroughly in the
ACL2 documentation; see the BOOKS node in the documentation tree.
Books should be ``certified'' before they are used. We do not distribute certificates with our books, mainly because certification produces compiled code specific to the host. You should certify the books locally as a test of your ACL2 image.
It is easy to re-certify all the distributed books in Unix/Linux. We recommend you do this. If you have entered ACL2, exit to the operating system, e.g., by control-d in many systems.
While connected to dir/acl2-sources, execute
make certify-booksThis will generate minimal output to the screen and will probably take an hour or two. Failure is indicated by the presence of
**CERTIFICATION FAILED** in the log.
To remove the files thus created, invoke:
make clean-books
The certify-books target does not cause workshop books to be
certified. If you want to certify those books as well, you will first need to
download
the gzipped tar file to the books/ directory, and then gunzip
and extract it. You can certify all the books, including books for the
workshops (including those from the 1999 workshop as described in the
(hardbound) book Computer-Aided
Reasoning: ACL2 Case Studies), using the command:
make regression
By default, certification uses the image
dir/acl2-sources/saved_acl2. You may specify any ACL2
image, as long as it is either a command on your Unix/Linux path or an absolute file
name, for example as follows.
make certify-books ACL2=my-acl2 make regression ACL2=/u/smith/projects/acl2/saved_acl2
We apologize to non-Unix/Linux users: we do not provide non-Unix/Linux
instructions for recertifying the distributed books. The
certification methods provided by the authors of the books vary
greatly and we codified them in the Unix/Linux makefile (GNUmakefile) used above. Most
subdirectories of acl2-sources/books contain either a
README file or a certify.lsp file. Users
who wish to certify one of these books and who cannot figure out (from
these scant clues) what to type to ACL2 should not hesitate to contact
the authors.
Next proceed to the section on Documentation.
ACL2's documentation is a hypertext document that, if printed in book form, is about 1100 pages or more than 2 megabytes of text. Its hypertext character makes it far more pleasing to read with an interactive browser. The documentation is available in four formats: HTML, Texinfo, Postscript and ACL2 documentation strings. All of this material is copyrighted by the University of Texas at Austin and is derived under the GNU General Public License from material copyrighted by Computational Logic, Inc.
Two Web-based guided tours of ACL2 are available from the home page
noted below. If you are already familiar with Nqthm, you might find
it useful to look at the documentation node
NQTHM-TO-ACL2. Another useful documentation topic for
beginning ACL2 users is the node TUTORIAL.
HTML
The ACL2 Home Page is
http://www.cs.utexas.edu/users/moore/acl2/index.html
The home page provides a selected bibliography, a search button (near the top of the page), guided tours of the system, and the complete hypertext documentation tree.
Once you have installed ACL2, the HTML form of the documentation is
available locally as
dir/acl2-sources/doc/HTML/acl2-doc.html.
We urge you to browse your local copy of the documentation rather than
our Web copy, simply to reduce Web traffic and the demand on our
server. (Macintosh users using MacOS 9 and earlier may, however, find
filenames being truncated and hence will want to avoid the local
documentation.)
Emacs Info
This is a very convenient format for accessing the ACL2 documentation from within Emacs. In Emacs, invoke
meta-x infoand then, if you are unfamiliar with Info, type
control-h mto see a list of commands available. In particular, type
g (dir/acl2-sources/doc/EMACS/acl2-doc-emacs.info)TOP* ACL2 i.j: (dir/acl2-sources/doc/EMACS/acl2-doc-emacs).Documentation for ACL2 version i.j.
acl2-sources/doc/texinfo.tex which
is copyrighted by the Free Software Foundation, Inc. (See that file
for copyright and license information.)
Users new to emacs may find it helpful to load into emacs the file
dir/acl2-sources/emacs/emacs-acl2.el. Utilities
offered by this file are documented near the top of the file.
Postscript
The Postscript version of the documentation is not included in our normal distribution because it is so much less useful than the hyper-text versions. But a gzipped Postscript (1.2 MB) version is available. It prints as a book of about 1000 pages and contains a Table of Contents and an index to all documented topics.
ACL2 Documentation Strings
The ACL2 system has facilities for browsing the documentation. When you are in
the ACL2 command loop, you may query the documentation on a given topic by
typing the command
:doc topic
where topic is the Lisp symbol naming the topic you want to
learn about. To learn more about the on-line documentation, type
:help and then return.
Note, however, that you may find it more convenient to view the documentation
in a web browser (starting at doc/HTML/acl2-doc.html) or in Emacs
info (starting at doc/EMACS/acl2-doc-emacs.info).
This completes the installation of ACL2 Version 3.1. You may wish to
return to the Table of Contents.
make utility, be sure that
you are using GNU make.
REAL for information about this
extension and how to build it, and a warning about its experimental nature.
if you care to use ACL2(r), first
download the non-standard analysis books (gzipped tar file) to the
Next build an executable image and certify books. First, connect to your
dir
By default, if no
This will create executable books/ subdirectory of your copy of the ACL2 distribution, say,
dir/acl2-sources/books/. Then run:
in the executable filename).
tar xvfz nonstd.tar.gz
/acl2-sources/ directory and execute
cd
acl2-sources
make large-acl2r LISP=xxx
where xxx is the command to run your local Common Lisp.
LISP=xxx is specified,
LISP=gcl is used. On our hosts, gcl is the name of
GNU Common Lisp, which can be obtained as explained above.
saved_acl2r in the
dir/acl2-sources directory (notice the trailing
~code>r
Finally, to certify books under directory
dir/acl2-sources/books/nonstd/ with ACL2(r), stand in the
dir/acl2-sources/ directory and execute the
following command.
make regression-nonstd ACL2=dir/acl2-sources/saved_acl2r
acl2-help@lists.cc.utexas.eduacl2@lists.cc.utexas.edu
http://www.cs.utexas.edu/users/moore/acl2/admin/forms/email.html.
You should receive a confirmation of the request a short time later,
along with instructions for use (e.g., how to retrieve
archive messages). If you need further assistance, please
send a message to
acl2-request@lists.cc.utexas.edu.
You can retrieve archive files or search the archives using a web interface
from
http://www.cs.utexas.edu/users/moore/acl2/admin/forms/archive.html.
You can search the ACL2 documentation, workshops, and publications online from
http://www.cs.utexas.edu/users/moore/acl2/admin/forms/search.html.
Finally, please report bugs in ACL2 to
acl2-bugs@lists.cc.utexas.edu.
This version of ACL2 is a descendent of ACL2 Version 1.9, Copyright (C) 1997 Computational Logic, Inc.
This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
Matt Kaufmann (Kaufmann@cs.utexas.edu)
J Strother Moore (Moore@cs.utexas.edu)
Department of Computer Sciences
University of Texas at Austin
Austin, TX 78712-1188 U.S.A.