# ACL2 Version 8.7

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 Common Lisp".

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

• | Start Here (including applications, talks, 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 8.6 | • | Other Releases

Matt Kaufmann and J Strother Moore
University of Texas at Austin
May 15, 2026

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.
- Documentation.
  There is an extensive user's manual that documents the ACL2 system and 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.
- Extensions.
  The ACL2 distribution includes the following extensions, which were developed by the individuals shown.
  - ACL2(r)
    Support for the real numbers by way of non-standard analysis
    Ruben Gamboa
  - ACL2(p)
    Support for parallel evaluation
    David L. Rager
  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 sources listed in the ACL2 acknowledgments page.

## The User's Manual

The ACL2+Books 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 START-HERE 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.

That manual not only includes documentation for the ACL2 system, 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 ACL2+Books Manual.

The following links take you to versions of the manual, which can be read not only in a Web browser, but also in the ACL2-Doc Emacs browser or by using the ACL2 `:DOC` command at the terminal. See the documentation topic, `DOCUMENTATION`.

- ACL2+Books Manual (Version 8.7)
- ACL2+Books Manual (for GitHub distributions)

You can build the ACL2+Books Manual locally, as follows, though this will likely take several minutes or even considerably longer, depending on which books you have already certified).

        cd acl2-sources/books
        # 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 file `books/doc/manual/index.html` under your ACL2 sources directory.

## 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 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 the `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 mechanism.)

## Searching documentation

The web views of the 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.