/usr/share/acl2-6.3/books/str/ is in acl2-books-certs 6.3-5.
This file is owned by root:root, with mode 0o755.
..
/usr/share/acl2-6.3/books/str/abbrevs.cert
/usr/share/acl2-6.3/books/str/arithmetic.cert
/usr/share/acl2-6.3/books/str/base64.cert
/usr/share/acl2-6.3/books/str/case-conversion.cert
/usr/share/acl2-6.3/books/str/cat.cert
/usr/share/acl2-6.3/books/str/char-case.cert
/usr/share/acl2-6.3/books/str/char-fix.cert
/usr/share/acl2-6.3/books/str/coerce.cert
/usr/share/acl2-6.3/books/str/defs.cert
/usr/share/acl2-6.3/books/str/digitp.cert
/usr/share/acl2-6.3/books/str/eqv.cert
/usr/share/acl2-6.3/books/str/explode-atom.cert
/usr/share/acl2-6.3/books/str/explode-nonnegative-integer.cert
/usr/share/acl2-6.3/books/str/fast-cat.cert
/usr/share/acl2-6.3/books/str/firstn-chars.cert
/usr/share/acl2-6.3/books/str/hexify.cert
/usr/share/acl2-6.3/books/str/html-encode.cert
/usr/share/acl2-6.3/books/str/ieqv.cert
/usr/share/acl2-6.3/books/str/iless.cert
/usr/share/acl2-6.3/books/str/iprefixp.cert
/usr/share/acl2-6.3/books/str/isort.cert
/usr/share/acl2-6.3/books/str/istrpos.cert
/usr/share/acl2-6.3/books/str/istrprefixp.cert
/usr/share/acl2-6.3/books/str/isubstrp.cert
/usr/share/acl2-6.3/books/str/make-character-list.cert
/usr/share/acl2-6.3/books/str/natstr.cert
/usr/share/acl2-6.3/books/str/pad.cert
/usr/share/acl2-6.3/books/str/portcullis.cert
/usr/share/acl2-6.3/books/str/prefix-lines.cert
/usr/share/acl2-6.3/books/str/stringify.cert
/usr/share/acl2-6.3/books/str/strline.cert
/usr/share/acl2-6.3/books/str/strnatless.cert
/usr/share/acl2-6.3/books/str/strpos.cert
/usr/share/acl2-6.3/books/str/strprefixp.cert
/usr/share/acl2-6.3/books/str/strrpos.cert
/usr/share/acl2-6.3/books/str/strsplit.cert
/usr/share/acl2-6.3/books/str/strsubst.cert
/usr/share/acl2-6.3/books/str/strtok.cert
/usr/share/acl2-6.3/books/str/strval.cert
/usr/share/acl2-6.3/books/str/subseq.cert
/usr/share/acl2-6.3/books/str/substrp.cert
/usr/share/acl2-6.3/books/str/suffixp.cert
/usr/share/acl2-6.3/books/str/symbols.cert
/usr/share/acl2-6.3/books/str/top.cert