/usr/share/acl2-8.0dfsg/books/projects/sb-machine/ is in acl2-books-source 8.0dfsg-1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/acl2-8.0dfsg/books/projects/sb-machine/cert.acl2
/usr/share/acl2-8.0dfsg/books/projects/sb-machine/portcullis.acl2
/usr/share/acl2-8.0dfsg/books/projects/sb-machine/portcullis.lisp
/usr/share/acl2-8.0dfsg/books/projects/sb-machine/proofs/
/usr/share/acl2-8.0dfsg/books/projects/sb-machine/proofs/completed/
/usr/share/acl2-8.0dfsg/books/projects/sb-machine/proofs/completed/fence.lisp
/usr/share/acl2-8.0dfsg/books/projects/sb-machine/proofs/completed/portcullis.acl2
/usr/share/acl2-8.0dfsg/books/projects/sb-machine/proofs/completed/portcullis.lisp
/usr/share/acl2-8.0dfsg/books/projects/sb-machine/proofs/completed/stupid.lisp
/usr/share/acl2-8.0dfsg/books/projects/sb-machine/proofs/completed/stupid2.lisp
/usr/share/acl2-8.0dfsg/books/projects/sb-machine/proofs/completed/stupid3.lisp
/usr/share/acl2-8.0dfsg/books/projects/sb-machine/proofs/completed/writes-with-fence-dumb.lisp
/usr/share/acl2-8.0dfsg/books/projects/sb-machine/proofs/completed/writes-with-fence-ghost.lisp
/usr/share/acl2-8.0dfsg/books/projects/sb-machine/proofs/completed/writes-with-fence.lisp
/usr/share/acl2-8.0dfsg/books/projects/sb-machine/sb.lisp
/usr/share/acl2-8.0dfsg/books/projects/sb-machine/tools.lisp