/usr/share/acl2-6.3/books/std/osets/ is in acl2-books-certs 6.3-5.
This file is owned by root:root, with mode 0o755.
..
/usr/share/acl2-6.3/books/std/osets/cardinality.cert
/usr/share/acl2-6.3/books/std/osets/computed-hints.cert
/usr/share/acl2-6.3/books/std/osets/delete.cert
/usr/share/acl2-6.3/books/std/osets/difference.cert
/usr/share/acl2-6.3/books/std/osets/instance.cert
/usr/share/acl2-6.3/books/std/osets/intersect.cert
/usr/share/acl2-6.3/books/std/osets/map-tests.cert
/usr/share/acl2-6.3/books/std/osets/map.cert
/usr/share/acl2-6.3/books/std/osets/membership.cert
/usr/share/acl2-6.3/books/std/osets/outer.cert
/usr/share/acl2-6.3/books/std/osets/portcullis.cert
/usr/share/acl2-6.3/books/std/osets/primitives.cert
/usr/share/acl2-6.3/books/std/osets/quantify.cert
/usr/share/acl2-6.3/books/std/osets/sort.cert
/usr/share/acl2-6.3/books/std/osets/top.cert
/usr/share/acl2-6.3/books/std/osets/under-set-equiv.cert
/usr/share/acl2-6.3/books/std/osets/union.cert