/usr/share/acl2-6.3/books/defexec/dag-unification/ is in acl2-books-certs 6.3-5.
This file is owned by root:root, with mode 0o755.
..
/usr/share/acl2-6.3/books/defexec/dag-unification/basic.cert
/usr/share/acl2-6.3/books/defexec/dag-unification/dag-unification-l.cert
/usr/share/acl2-6.3/books/defexec/dag-unification/dag-unification-rules.cert
/usr/share/acl2-6.3/books/defexec/dag-unification/dag-unification-st.cert
/usr/share/acl2-6.3/books/defexec/dag-unification/dags.cert
/usr/share/acl2-6.3/books/defexec/dag-unification/list-unification-rules.cert
/usr/share/acl2-6.3/books/defexec/dag-unification/matching.cert
/usr/share/acl2-6.3/books/defexec/dag-unification/subsumption-subst.cert
/usr/share/acl2-6.3/books/defexec/dag-unification/subsumption.cert
/usr/share/acl2-6.3/books/defexec/dag-unification/terms-as-dag.cert
/usr/share/acl2-6.3/books/defexec/dag-unification/terms-dag-stobj.cert
/usr/share/acl2-6.3/books/defexec/dag-unification/terms.cert