NOTE-2-4.html -- ACL2 Version 6.3

## NOTE-2-4

ACL2 Version 2.4 (August, 1999) Notes

    Major Section:  RELEASE-NOTES

Important changes:

We corrected a soundness bug in Version 2.3 related to the handling of `immediate-force-modep`. The bad behavior was noticed by Robert Krug. Thanks!

We corrected a bug that permitted `verify-guards` to accept a function even though a subfunction had not yet had its guards verified. Thanks to John Cowles for noticing this.

User defined single-threaded objects are now supported. See stobj.

Less important notes:

We corrected a bug that prevented the intended expansion of some recursive function calls.

We changed the handling of the primitive function `ILLEGAL`, which is logically defined to be `nil` but which is programmed to signal an error, so that when it is evaluated as part of a proof, it does not signal an error. The old handling of the function prevented some guard proofs involving `THE` or `LET`s with internal declarations.

We corrected a bug that permitted some `LOCAL` `DEFAXIOM` events to slip into certified books.

We corrected a bug that prevented the correct undoing of certain `DEFPKG` forms.

Changes were made to support CMU Lisp. Pete Manolios helped with these changes.

Changes were made to make the make files more compatible with Allegro Common Lisp. Jun Sawada, who has been a great help with keeping ACL2 up and running at UT on various platforms, was especially helpful. Thanks Jun.