/usr/share/acl2-7.1/books/std/strings/ is in acl2-books-source 7.1-1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/acl2-7.1/books/std/strings/abbrevs.lisp
/usr/share/acl2-7.1/books/std/strings/arithmetic.lisp
/usr/share/acl2-7.1/books/std/strings/base64.lisp
/usr/share/acl2-7.1/books/std/strings/binary.lisp
/usr/share/acl2-7.1/books/std/strings/case-conversion.lisp
/usr/share/acl2-7.1/books/std/strings/cat.lisp
/usr/share/acl2-7.1/books/std/strings/cert.acl2
/usr/share/acl2-7.1/books/std/strings/char-case.lisp
/usr/share/acl2-7.1/books/std/strings/char-fix.lisp
/usr/share/acl2-7.1/books/std/strings/charset-fns.lisp
/usr/share/acl2-7.1/books/std/strings/charset.lisp
/usr/share/acl2-7.1/books/std/strings/coerce.lisp
/usr/share/acl2-7.1/books/std/strings/decimal.lisp
/usr/share/acl2-7.1/books/std/strings/defs-aux.lisp
/usr/share/acl2-7.1/books/std/strings/defs-program.lisp
/usr/share/acl2-7.1/books/std/strings/defs.lisp
/usr/share/acl2-7.1/books/std/strings/eqv.lisp
/usr/share/acl2-7.1/books/std/strings/explode-atom.lisp
/usr/share/acl2-7.1/books/std/strings/explode-nonnegative-integer.lisp
/usr/share/acl2-7.1/books/std/strings/fast-cat.lisp
/usr/share/acl2-7.1/books/std/strings/firstn-chars.lisp
/usr/share/acl2-7.1/books/std/strings/hex.lisp
/usr/share/acl2-7.1/books/std/strings/hexify.lisp
/usr/share/acl2-7.1/books/std/strings/html-encode.lisp
/usr/share/acl2-7.1/books/std/strings/ieqv.lisp
/usr/share/acl2-7.1/books/std/strings/iless.lisp
/usr/share/acl2-7.1/books/std/strings/iprefixp.lisp
/usr/share/acl2-7.1/books/std/strings/isort.lisp
/usr/share/acl2-7.1/books/std/strings/istrpos.lisp
/usr/share/acl2-7.1/books/std/strings/istrprefixp.lisp
/usr/share/acl2-7.1/books/std/strings/isubstrp.lisp
/usr/share/acl2-7.1/books/std/strings/make-character-list.lisp
/usr/share/acl2-7.1/books/std/strings/octal.lisp
/usr/share/acl2-7.1/books/std/strings/pad.lisp
/usr/share/acl2-7.1/books/std/strings/prefix-lines.lisp
/usr/share/acl2-7.1/books/std/strings/pretty-defs-aux.lisp
/usr/share/acl2-7.1/books/std/strings/pretty-defs.lisp
/usr/share/acl2-7.1/books/std/strings/pretty-program.lisp
/usr/share/acl2-7.1/books/std/strings/pretty-tests.acl2
/usr/share/acl2-7.1/books/std/strings/pretty-tests.lisp
/usr/share/acl2-7.1/books/std/strings/pretty.lisp
/usr/share/acl2-7.1/books/std/strings/stringify.lisp
/usr/share/acl2-7.1/books/std/strings/strline.lisp
/usr/share/acl2-7.1/books/std/strings/strnatless.lisp
/usr/share/acl2-7.1/books/std/strings/strpos.lisp
/usr/share/acl2-7.1/books/std/strings/strprefixp.lisp
/usr/share/acl2-7.1/books/std/strings/strrpos.lisp
/usr/share/acl2-7.1/books/std/strings/strsplit.lisp
/usr/share/acl2-7.1/books/std/strings/strsubst.lisp
/usr/share/acl2-7.1/books/std/strings/strtok.lisp
/usr/share/acl2-7.1/books/std/strings/subseq.lisp
/usr/share/acl2-7.1/books/std/strings/substrp.lisp
/usr/share/acl2-7.1/books/std/strings/suffixp.lisp
/usr/share/acl2-7.1/books/std/strings/symbols.lisp
/usr/share/acl2-7.1/books/std/strings/top.lisp