ACL2 Version 8.4
ACL2 is a logic and programming language in which you can model
computer systems, together with a tool to help you prove properties
of those models. "ACL2" denotes
"A Computational Logic for Applicative
ACL2 is part of the Boyer-Moore family of provers, for which its authors have
received the 2005 ACM
Software System Award.
Matt Kaufmann and J Strother Moore
University of Texas at Austin
August 5, 2021
Welcome to the ACL2 home page! We highlight a few aspects of ACL2:
- Libraries (Books).
Libraries of books (files containing
definitions and theorems) extend the code that we have written. In particular,
the distribution tarball includes the community books, which are
contributed and maintained by the members of the ACL2 community.
There is an
extensive user's manual for the ACL2 system, and an even more comprehensive
manual that documents not only the ACL2 system but also many community books.
See below to learn more.
- License and Copyright.
ACL2 is freely available under the terms
of the LICENSE file distributed with ACL2. License, copyright, and
authorship information is available from the ACL2 documentation.
The ACL2 distribution includes the following
extensions, which were developed by the individuals shown. NOTE:Not
included in this list is what was formerly known as "ACL2(h)", because it is
now the default build of ACL2: that is, ACL2 builds are now hons-enabled. Thanks to Bob Boyer, Warren A. Hunt, Jr., Jared
Davis, and Sol Swords for their contributions; see the acknowledgments.
Another extension of ACL2 is the Eclipse-based ACL2 Sedan (ACL2s). Unlike
the systems above, ACL2s is distributed and maintained by Pete Manolios and his
research group. ACL2s comes with a standard executable ACL2 image for Windows,
but it also comes with pre-certified community books and an extension of ACL2
with additional features, including extra automation for termination proofs as
well as counterexample generation.
Support for the real numbers by way of non-standard analysis
Support for parallel evaluation
David L. Rager
We gratefully acknowledge substantial support from the following. (These are
included in a much more complete acknowledgments page.)
- National Science Foundation
- This material is based upon work supported by the National Science
Foundation under Grant Nos. CCF-1526760, CNS-1525472, CCF-1153558,
EIA-0303609, CNS-0429591, ISS-0417413, CCF-0945316, and CNS-0910913.
- Any opinions, findings and conclusions or recomendations expressed in
this material are those of the authors and do not necessarily reflect the
views of the National Science Foundation.
- Advanced Micro Devices, Inc.
- ForrestHunt, Inc.
- Rockwell Collins, Inc.
- Sun Microsystems, Inc.
The ACL2 User's Manual is a vast hypertext document. If you are a
newcomer to ACL2, we do not recommend that you wander off into the
full documentation. Instead start with the ACL2-TUTORIAL
documentation topic. Experienced users tend mostly to use the manual as a
reference manual, to look up concepts mentioned in error messages or vaguely
remembered from their past experiences with ACL2.
The ACL2+Books Manual includes not only the ACL2 User's Manual, but also
documents many of the community books (libraries). This
manual, which is written by many authors, is thus more extensive than the ACL2
system, and is thus potentially more useful. With the exception of the first
bulleted link below, links to the manual on this page will all take you to the
The following links take you to these two manuals. The manuals can however be
read not only in a Web browser, but in the ACL2-Doc Emacs
browser or by using the ACL2
at the terminal; see the documentation topic,
Once you have installed ACL2, you can browse the ACL2 User's Manual locally by
viewing a copy of this home page under your ACL2 sources directory at
doc/home-page.html and following the last link shown above; but
first you will need to run the following command in your ACL2 sources
make DOC ACL2=<path_to_your_ACL2>
Better yet, you can build the ACL2+Books Manual locally, as follows, though
this will likely take longer (perhaps a half hour or more, depending on which
books you have already certified).
# The following uses ccl by default; sbcl is also acceptable.
make manual ACL2=<path_to_your_ACL2>
The resulting ACL2+Books Manual may be accessed by pointing your browser to the
books/doc/manual/index.html under your ACL2 sources directory.
A companion to ACL2 is the library of community books, which have been
developed by many users over the years. These books contain definitions and
theorems that you might find useful in your models and proofs. In addition,
some books contain ACL2 tools built by users to help with reasoning,
programming, interfaces, debugging, and testing; see
the documentation. Some relevant papers may be found by following links in
the pages on
Books and Papers about ACL2 and Its Applications and the ACL2 Workshops
Series. The installation
instructions explain how to download and install the community books.
We strongly encourage users to submit additional books and to improve existing
books. If you have interest in contributing, there is a documentation topic to get you started. You can also visit
ACL2 System and
Books project page on github (just move past the big list of files
to find descriptive text). Project members are welcome to edit community
books. In particular, the community book
books/system/doc/acl2-doc.lisp contains the ACL2 system
documentation, and project members are welcome to improve it.
(Prior to ACL2 Version 7.0 (January, 2015) books were distributed through a different
The web views of The ACL2 User's Manual and ACL2+Books
Manual allow you to search the short strings of the documentation (which
are typically summaries of a line or so). To search the full content for a
string or regular expression, you may use the Emacs-based ACL2-Doc browser.