/usr/share/acl2-8.0dfsg/books/misc/redef-pkg.acl2 is in acl2-books-source 8.0dfsg-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | ; cert-flags: ? t :ttags (:redef-pkg)
(certify-book "redef-pkg" ? t :ttags (:redef-pkg))
|