/usr/share/acl2-6.3/books/cgen/ is in acl2-books-certs 6.3-5.
This file is owned by root:root, with mode 0o755.
..
/usr/share/acl2-6.3/books/cgen/acl2s-parameter.cert
/usr/share/acl2-6.3/books/cgen/base.cert
/usr/share/acl2-6.3/books/cgen/basis.cert
/usr/share/acl2-6.3/books/cgen/defdata.cert
/usr/share/acl2-6.3/books/cgen/elim.cert
/usr/share/acl2-6.3/books/cgen/graph-tc.cert
/usr/share/acl2-6.3/books/cgen/library-support.cert
/usr/share/acl2-6.3/books/cgen/main.cert
/usr/share/acl2-6.3/books/cgen/mv-proof.cert
/usr/share/acl2-6.3/books/cgen/num-list-fns.cert
/usr/share/acl2-6.3/books/cgen/num-list-thms.cert
/usr/share/acl2-6.3/books/cgen/random-state-basis1.cert
/usr/share/acl2-6.3/books/cgen/random-state.cert
/usr/share/acl2-6.3/books/cgen/random.cert
/usr/share/acl2-6.3/books/cgen/rem-and-floor.cert
/usr/share/acl2-6.3/books/cgen/simple-graph-array.cert
/usr/share/acl2-6.3/books/cgen/splitnat.cert
/usr/share/acl2-6.3/books/cgen/switchnat.cert
/usr/share/acl2-6.3/books/cgen/top.cert
/usr/share/acl2-6.3/books/cgen/type.cert
/usr/share/acl2-6.3/books/cgen/utilities.cert
/usr/share/acl2-6.3/books/cgen/with-timeout.cert