/usr/share/acl2-6.3/books/centaur/bitops/ is in acl2-books-source 6.3-5.
This file is owned by root:root, with mode 0o755.
..
/usr/share/acl2-6.3/books/centaur/bitops/ash-bounds.lisp
/usr/share/acl2-6.3/books/centaur/bitops/bits-between.lisp
/usr/share/acl2-6.3/books/centaur/bitops/bitsets-opt.lisp
/usr/share/acl2-6.3/books/centaur/bitops/bitsets.lisp
/usr/share/acl2-6.3/books/centaur/bitops/cert.acl2
/usr/share/acl2-6.3/books/centaur/bitops/congruences.lisp
/usr/share/acl2-6.3/books/centaur/bitops/defaults.lisp
/usr/share/acl2-6.3/books/centaur/bitops/equal-by-logbitp.lisp
/usr/share/acl2-6.3/books/centaur/bitops/extra-defs.lisp
/usr/share/acl2-6.3/books/centaur/bitops/ihs-extensions.lisp
/usr/share/acl2-6.3/books/centaur/bitops/ihsext-basics.lisp
/usr/share/acl2-6.3/books/centaur/bitops/install-bit.lisp
/usr/share/acl2-6.3/books/centaur/bitops/integer-length.lisp
/usr/share/acl2-6.3/books/centaur/bitops/part-select.lisp
/usr/share/acl2-6.3/books/centaur/bitops/rotate.acl2
/usr/share/acl2-6.3/books/centaur/bitops/rotate.lisp
/usr/share/acl2-6.3/books/centaur/bitops/saturate.lisp
/usr/share/acl2-6.3/books/centaur/bitops/sbitsets.lisp
/usr/share/acl2-6.3/books/centaur/bitops/sign-extend.lisp
/usr/share/acl2-6.3/books/centaur/bitops/signed-byte-p.lisp
/usr/share/acl2-6.3/books/centaur/bitops/top.lisp