ACL2 Version 6.3

ACL2 is both a programming language in which you can model computer systems and a tool to help you prove properties of those models.

ACL2 is part of the Boyer-Moore family of provers, for which its authors have received the 2005 ACM Software System Award.


Start Here: Applications, Tours, and Tutorials/Demos ACL2 Workshops, UT Seminar, and Course Materials
Publications about ACL2 and Its Applications The User's Manual and Hyper-Card
Community Books: Lemma Libraries and Utilities Mailing Lists
Recent changes to this page Obtaining, Installing, and License
Differences from Version 6.2 Other Releases
How to contribute libraries and documentation

Matt Kaufmann and J Strother Moore
University of Texas at Austin
September 30, 2013

Libraries of books (files containing definitions and theorems) extend the code that we have written. These community books are contributed and maintained by the members of the ACL2 community; see the acl2-books project page.

The libraries and the ACL2 source code are under revision control, using svn. Experimental copies of ACL2 and the libraries are thus available between ACL2 releases. The authors of ACL2 consider svn distributions to be experimental; while they will likely be fully functional in most cases, they could however be incomplete, fragile, and unable to pass our own regression. If you decide to use svn versions of either the libraries or ACL2, then you should use both, as they tend to be kept in sync. See the project websites, acl2-books and acl2-devel, for the ACL2 libraries and development sources, respectively.

A combined manual, known as the acl2+books combined (xdoc) manual, incorporates not only The User's Manual for ACL2 (with some topics rearranged) but also documentation for many books. Thanks to Jared Davis for building the xdoc processor for creating this view of the documentation. We frequently make available recent svn copies of the manual.

The ACL2 distribution includes the following extensions, which were contributed by the individuals shown.

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.

We gratefully acknowledge substantial support from the following. (These are included in a much more complete acknowledgments page.)

The User's Manual

ACL2's user manual is a vast hypertext document. You can wander through it here, in its HTML format.

Here are the two common entries to the documentation graph:
Major Topics (Table of Contents)
Index of all documented topics
The tiny warning signs, , indicate that the links lead out of introductory level material and into reference manual material. Once in the reference manual, virtually all links are into the manual and none of them is marked with the warning sign! It is easy for the newcomer to get lost.

Here is how we recommend you use this documentation.

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 ``Index'' to look up concepts mentioned in error messages or vaguely remembered from their past experiences with ACL2.

Note: The documentation is available for reading in a Web browser (recommended), in Emacs Info, using the ACL2 :DOC command, or as a printed book (over 2200 pages). These are available as follows.

Community Books: Lemma Libraries and Utilities, and How to Contribute

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 reasoning or analysis tools built by users. The installation instructions explain how to download and install the community books.

We strongly encourage users to submit additional books by following the instructions at the acl2-books project page hosted at

We also distribute a few interface tools, such as support for infix printing. For these, see the Utilities section of Books and Papers about ACL2 and Its Applications. Some of the papers mentioned in that collection contain utilities, scripts, or ACL2 books for the problem domains in question.

How to contribute libraries and documentation

As mentioned above, we strongly encourage users to submit additional books by following the instructions at the acl2-books project page hosted at

Also, if you have written up (or are interested in writing) text that may be helpful to other ACL2 users, we invite you to contribute it to the community. Such user documentation may be in any format that is readable by web browsers (for example html, pdf, and plain text). User-contributed documentation can link back to the ACL2 documentation proper, by using links such as:
(In general, substitute the upper-case of the documentation topic for "MAKE-EVENT" in the example above.)

To contribute user documentation, send email to the ACL2 developers, Matt Kaufmann and J Strother Moore.

Searching documentation and books

The links below may help you to search the ACL2 documentation and the ACL2 community books, respectively. Our approach is low-tech, but intended to be reliable and easy to use on any platform. You might want to add a bookmark for each of these.