code: public Set<ClassExpression> getGeneratorSubConcepts() {
  		if (gens.size() == 1)
  			return gens.iterator().next().getSubConcepts();
  		
  		Set<ClassExpression> all = new HashSet<ClassExpression>();		
  		for (TreeWitnessGenerator twg : gens) 
  			all.addAll(twg.getSubConcepts());
  		return all;
  	}
docs: getGeneratorSubConcepts
  
  @return the set of all sub-concepts for all of the tree witness generators