/usr/share/acl2-6.3/books/parallel/ is in acl2-books-source 6.3-5.
This file is owned by root:root, with mode 0o755.
..
/usr/share/acl2-6.3/books/parallel/cert.acl2
/usr/share/acl2-6.3/books/parallel/fibonacci.lisp
/usr/share/acl2-6.3/books/parallel/hint-tests.lisp
/usr/share/acl2-6.3/books/parallel/matrix-multiplication-parallel.lisp
/usr/share/acl2-6.3/books/parallel/matrix-multiplication-serial.lisp
/usr/share/acl2-6.3/books/parallel/matrix-multiplication-setup.lisp
/usr/share/acl2-6.3/books/parallel/proofs/
/usr/share/acl2-6.3/books/parallel/proofs/ideal-speedup.lisp
/usr/share/acl2-6.3/books/parallel/spec-mv-let.lisp
/usr/share/acl2-6.3/books/parallel/stress-tests.lisp
/usr/share/acl2-6.3/books/parallel/syntax-tests.lisp
/usr/share/acl2-6.3/books/parallel/with-waterfall-parallelism.lisp
/usr/share/acl2-6.3/books/parallel/without-waterfall-parallelism.lisp