Modify the logic programming interpreter to handle or and not. Disjunctive expressions should succeed if at least one of the disjuncts succeeds; in processing a disjunctive expression, the interpreter should return the union of all the solutions returned by the disjuncts. Negation is a bit more difficult, since a negated goal can succeed only if the goal itself fails. Thus, it is not possible to return any variable bindings for a negated goal. This is a result of the closed world assumption and negation as failure described in Section 13.3.