/usr/share/acl2-7.1/books/defexec/dag-unification/ is in acl2-books 7.1-1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/acl2-7.1/books/defexec/dag-unification/basic.o
/usr/share/acl2-7.1/books/defexec/dag-unification/dag-unification-l.o
/usr/share/acl2-7.1/books/defexec/dag-unification/dag-unification-rules.o
/usr/share/acl2-7.1/books/defexec/dag-unification/dag-unification-st.o
/usr/share/acl2-7.1/books/defexec/dag-unification/dags.o
/usr/share/acl2-7.1/books/defexec/dag-unification/list-unification-rules.o
/usr/share/acl2-7.1/books/defexec/dag-unification/matching.o
/usr/share/acl2-7.1/books/defexec/dag-unification/subsumption-subst.o
/usr/share/acl2-7.1/books/defexec/dag-unification/subsumption.o
/usr/share/acl2-7.1/books/defexec/dag-unification/terms-as-dag.o
/usr/share/acl2-7.1/books/defexec/dag-unification/terms-dag-stobj.o
/usr/share/acl2-7.1/books/defexec/dag-unification/terms.o