/**
  * Explains why class {@code cl} is unsatisfiable
  *
  * @param cl The class to check for unsatisfiability
  * @return The explanation {@link org.openrdf.model.Graph Graph}
  * @throws PelletClientException If there is an error or {@code cl} is not unsatisfiable
  */
 public Graph unsat(Resource cl) throws PelletClientException {
   String query =
       selectQuery(
           cl.stringValue(),
           RDFS.SUBCLASSOF.stringValue(),
           "http://www.w3.org/2002/07/owl#Nothing");
   return query(query);
 }
 /**
  * Asynchronously explains why class {@code cl} is unsatisfiable
  *
  * @param cl The class to check for unsatisfiability
  * @param callback The {@link Callback} to execute after the explanation is done
  */
 public void unsat(Resource cl, Callback<Graph> callback) {
   String query =
       selectQuery(
           cl.stringValue(),
           RDFS.SUBCLASSOF.stringValue(),
           "http://www.w3.org/2002/07/owl#Nothing");
   query(query, callback);
 }
 /**
  * Explains why {@code subclass} is rdfs:subclassOf {@code superclass}
  *
  * @param subclass The sub class
  * @param superclass The super class
  * @return The explanation {@link org.openrdf.model.Graph Graph}
  * @throws PelletClientException if there is an error while querying
  */
 public Graph subclass(Resource subclass, Resource superclass) throws PelletClientException {
   String query =
       selectQuery(
           subclass.stringValue(), RDFS.SUBCLASSOF.stringValue(), superclass.stringValue());
   return query(query);
 }
 /**
  * Asynchronously explains why {@code subclass} is rdfs:subclassOf {@code superclass}
  *
  * @param subclass The sub class
  * @param superclass The super class
  * @param callback The {@link Callback} to execute after the explanation is done
  */
 public void subclass(Resource subclass, Resource superclass, Callback<Graph> callback) {
   String query =
       selectQuery(
           subclass.stringValue(), RDFS.SUBCLASSOF.stringValue(), superclass.stringValue());
   query(query, callback);
 }