/usr/share/acl2-6.5/books/cgen/ is in acl2-books-source 6.5-2.
This file is owned by root:root, with mode 0o755.
..
/usr/share/acl2-6.5/books/cgen/acl2s-parameter.lisp
/usr/share/acl2-6.5/books/cgen/base.lisp
/usr/share/acl2-6.5/books/cgen/basis.lisp
/usr/share/acl2-6.5/books/cgen/cert.acl2
/usr/share/acl2-6.5/books/cgen/defdata.lisp
/usr/share/acl2-6.5/books/cgen/elim.lisp
/usr/share/acl2-6.5/books/cgen/graph-tc.lisp
/usr/share/acl2-6.5/books/cgen/library-support.lisp
/usr/share/acl2-6.5/books/cgen/main.lisp
/usr/share/acl2-6.5/books/cgen/mv-proof.lisp
/usr/share/acl2-6.5/books/cgen/num-list-fns.lisp
/usr/share/acl2-6.5/books/cgen/num-list-thms.lisp
/usr/share/acl2-6.5/books/cgen/random-state-basis1.lisp
/usr/share/acl2-6.5/books/cgen/random-state.lisp
/usr/share/acl2-6.5/books/cgen/random.lisp
/usr/share/acl2-6.5/books/cgen/rem-and-floor.lisp
/usr/share/acl2-6.5/books/cgen/simple-graph-array.lisp
/usr/share/acl2-6.5/books/cgen/splitnat.lisp
/usr/share/acl2-6.5/books/cgen/switchnat.lisp
/usr/share/acl2-6.5/books/cgen/top.lisp
/usr/share/acl2-6.5/books/cgen/type.lisp
/usr/share/acl2-6.5/books/cgen/utilities.lisp
/usr/share/acl2-6.5/books/cgen/with-timeout.lisp