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