/usr/share/acl2-7.1/books/data-structures/set-defthms.o is in acl2-books 7.1-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/acl2-7.1/books/data-structures/../../../../lib/acl2-7.1/books/data-structures/set-defthms.o