NOTE-2-6-SYSTEM.html -- ACL2 Version 6.3

### NOTE-2-6-SYSTEM

ACL2 Version 2.6 Notes on System-level Changes

    Major Section:  NOTE-2-6

We modified the tracking of `skip-proofs` events and the use of `state` global `ld-skip-proofsp` in order to avoid some soundness issues. For example, `skip-proofs` events buried in locally-included books are now tracked. The ``Essay on Skip-proofs'' in source file `axioms.lisp` gives several examples of dicey behavior that is no longer supported.

We fixed a problem with some of the makefiles, so that recursive invocations of `make' now use the version of `make' specified on the command line.

Files were fixed to help non-Unix/Linux users with book certification. Thanks to John Cowles for finding some problems and suggesting fixes to `books/certify-numbers.lisp`, `books/arithmetic/certify.lsp`, and `books/cowles/certify.lsp`. We thank Scott Burson for noticing and fixing some other such problems. Moreover, a bdd test was being ignored entirely in Version 2.5; this problem has been fixed as well.

A minor change in system function save-acl2-in-allegro will allow this function to continue to work in Allegro CL versions starting (someday) with 10.0. Thanks to Art Flatau for suggesting such a fix.

The `books/case-studies/` directory has been removed. These books are in support of the first (1998) ACL2 workshop, and are accessible via the ACL2 home page on the Web, http://www.cs.utexas.edu/users/moore/acl2/. Also, the `books/cli-misc` directory has been renamed `books/misc`, and the `books/nqthm` directory has been removed.

The notion of ACL2 version has been slightly modified to catch unsoundness due to implementation dependencies. See version. Another change to eliminate such unsoundness is that built-in symbols now have a `symbol-package-name` of `"COMMON-LISP"`; formerly, this string was `"LISP"` for ACL2 images built on GCL. See symbol-package-name. At a low level, the (undocumented) constant `*main-lisp-package-name*` is now `"COMMON-LISP"`; before, it was `"LISP"` for GCL.