/usr/share/acl2-6.5/books/str/strnatless.lisp is in acl2-books-source 6.5-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | (in-package "ACL2")
; cert_param: (reloc_stub)
(include-book "std/strings/strnatless" :dir :system)
|