/usr/share/acl2-6.3/books/finite-set-theory/ is in acl2-books-source 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.lisp
/usr/share/acl2-6.3/books/finite-set-theory/osets/computed-hints.lisp
/usr/share/acl2-6.3/books/finite-set-theory/osets/delete.lisp
/usr/share/acl2-6.3/books/finite-set-theory/osets/difference.lisp
/usr/share/acl2-6.3/books/finite-set-theory/osets/instance.lisp
/usr/share/acl2-6.3/books/finite-set-theory/osets/intersect.lisp
/usr/share/acl2-6.3/books/finite-set-theory/osets/map-tests.lisp
/usr/share/acl2-6.3/books/finite-set-theory/osets/map.lisp
/usr/share/acl2-6.3/books/finite-set-theory/osets/membership.lisp
/usr/share/acl2-6.3/books/finite-set-theory/osets/outer.lisp
/usr/share/acl2-6.3/books/finite-set-theory/osets/portcullis.lisp
/usr/share/acl2-6.3/books/finite-set-theory/osets/primitives.lisp
/usr/share/acl2-6.3/books/finite-set-theory/osets/quantify.lisp
/usr/share/acl2-6.3/books/finite-set-theory/osets/sets.lisp
/usr/share/acl2-6.3/books/finite-set-theory/osets/sort.lisp
/usr/share/acl2-6.3/books/finite-set-theory/osets/under-set-equiv.lisp
/usr/share/acl2-6.3/books/finite-set-theory/osets/union.lisp
/usr/share/acl2-6.3/books/finite-set-theory/set-theory.acl2
/usr/share/acl2-6.3/books/finite-set-theory/set-theory.lisp
/usr/share/acl2-6.3/books/finite-set-theory/total-ordering.lisp