boolean clash(OWLIndividual node)
	{
		HashSet<OWLClassExpression> labels = nodeLabels.get(node);
		if(labels.contains(factory.getOWLNothing()))
			return true;
		for(OWLClassExpression exp:labels)
			if(labels.contains(exp.getComplementNNF()))
				return true;
		return false;
	}