ACL2 Version 2.7 Notes on Changes in Rules and Constants
Major Section:  NOTE-2-7

The defcong macro has been slightly changed. The difference is that the variable generated with suffix -EQUIV will now be in the same package as the name of the variable from which it is generated, rather than always belonging to the ACL2 package. Thanks to Hanbing Liu for suggesting this change. (Note that a couple of books have been modified to accommodate this change, e.g., books/finite-set-theory/set-theory.)

In Version_2.6, a change was made for rules of class :rewrite whose conclusion is a term of the form (EQV lhs rhs), where EQV is =, eq, or eql: the rule was stored as though EQV were equal. (See note-2-6-rules.) This change has been extended to rules of class :definition.