code: @Override
      public Node<OWLClass> getUnsatisfiableClasses()
              throws ReasonerInterruptedException, TimeOutException,
              InconsistentOntologyException {
          return nodeToOwlClassNode(getTaxonomy().getBottomNode());
      }
docs: A convenience method that obtains the classes in the signature of the
  root ontology that are unsatisfiable.
  
  @return A <code>Node</code> that is the bottom node in the class
  hierarchy. This node represents <code>owl:Nothing</code> and
  contains <code>owl:Nothing</code> itself plus classes that are
  equivalent to <code>owl:Nothing</code>.
  
  @throws ReasonerInterruptedException
  if the reasoning process was interrupted for any particular
  reason (for example if reasoning was cancelled by a client
  process)
  @throws TimeOutException
  if the reasoner timed out during a basic reasoning operation.
  See {@link #getTimeOut()}.
  @throws InconsistentOntologyException
  if the set of reasoner axioms is inconsistent