/usr/share/acl2-6.3/books/system/ is in acl2-books-certs 6.3-5.
This file is owned by root:root, with mode 0o755.
..
/usr/share/acl2-6.3/books/system/compare-out-files.cert
/usr/share/acl2-6.3/books/system/convert-normalized-term-to-pairs.cert
/usr/share/acl2-6.3/books/system/deps-pcert.cert
/usr/share/acl2-6.3/books/system/extend-pathname.cert
/usr/share/acl2-6.3/books/system/f-put-global.cert
/usr/share/acl2-6.3/books/system/gather-dcls.cert
/usr/share/acl2-6.3/books/system/hl-addr-combine.cert
/usr/share/acl2-6.3/books/system/legal-variablep.cert
/usr/share/acl2-6.3/books/system/meta-extract.cert
/usr/share/acl2-6.3/books/system/origin.cert
/usr/share/acl2-6.3/books/system/pcert/
/usr/share/acl2-6.3/books/system/pcert/acl2x-pcert-test-1.cert/
/usr/share/acl2-6.3/books/system/pcert/acl2x-pcert-test-1.cert/acl2x-pcert-test-1.pcert0
/usr/share/acl2-6.3/books/system/pcert/acl2x-pcert-test-2-include.cert/
/usr/share/acl2-6.3/books/system/pcert/acl2x-pcert-test-2-include.cert/acl2x-pcert-test-2-include.pcert0
/usr/share/acl2-6.3/books/system/pcert/acl2x-pcert-test-2.cert/
/usr/share/acl2-6.3/books/system/pcert/acl2x-pcert-test-2.cert/acl2x-pcert-test-2.pcert0
/usr/share/acl2-6.3/books/system/pcert/elide-test.cert/
/usr/share/acl2-6.3/books/system/pcert/elide-test.cert/elide-test.pcert0
/usr/share/acl2-6.3/books/system/pcert/mid.cert/
/usr/share/acl2-6.3/books/system/pcert/mid.cert/mid.pcert0
/usr/share/acl2-6.3/books/system/pcert/pkg-test.cert/
/usr/share/acl2-6.3/books/system/pcert/pkg-test.cert/pkg-test.pcert0
/usr/share/acl2-6.3/books/system/pcert/sub.cert/
/usr/share/acl2-6.3/books/system/pcert/sub.cert/sub.pcert0
/usr/share/acl2-6.3/books/system/pcert/top.cert/
/usr/share/acl2-6.3/books/system/pcert/top.cert/top.pcert0
/usr/share/acl2-6.3/books/system/pseudo-good-worldp.cert
/usr/share/acl2-6.3/books/system/pseudo-termp-lemmas.cert
/usr/share/acl2-6.3/books/system/random.cert
/usr/share/acl2-6.3/books/system/subcor-var.cert
/usr/share/acl2-6.3/books/system/sublis-var.cert
/usr/share/acl2-6.3/books/system/subst-expr.cert
/usr/share/acl2-6.3/books/system/subst-var.cert
/usr/share/acl2-6.3/books/system/too-many-ifs.cert
/usr/share/acl2-6.3/books/system/top.cert
/usr/share/acl2-6.3/books/system/update-state.cert
/usr/share/acl2-6.3/books/system/verified-termination-and-guards.cert
/usr/share/acl2-6.3/books/system/worldp-check.cert