books/ subdirectory,
the community
books (libraries).  The ACL2 system is developed at the
University of Texas at Austin
and can also be
obtained or explored separately.
acl2-sources or acl2-8.1.  Then use
either of the following two methods to obtain the ACL2 source code and
community books.
  acl2-8.1.tar.gz from GitHub and
      then execute:tar xfz acl2-8.1.tar.gzacl2-8.1.
    Connect to acl2-8.1.git clone https://github.com/acl2/acl2 acl2-sourcesacl2-sources.
      Connect to acl2-sources/.
    make LISP=<path_to_your_lisp_executable>
saved_acl2.make certify-booksor something fancier such as the following:
(time nice make -j 8 ACL2=/u/smith/bin/acl2 certify-books) >& make-certify-books.logThis may take less than 2 hours or much longer (perhaps 8 hours, perhaps even more), depending on your machine and host Common Lisp. The resulting log file,
make-certify-books.log, should
contain no occurrences of the string ``CERTIFICATION FAILED''; a
normal exit (status 0) should guarantee this.  If you want additional
explanation and further options, see the documentation
for BOOKS-CERTIFICATION.
saved_acl2 (from step 3)
and access to certified community books (from step 4).  Enjoy!