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