code: @Override
  	public Collection<BioPAXElement> generate(Match match, int... ind)
  	{
  		Collection<BioPAXElement> gen = new HashSet<BioPAXElement> (
  			con[0].generate(match, ind));
  
  		for (int i = 1; i < con.length; i++)
  		{
  			if (gen.isEmpty()) break;
  
  			Collection<BioPAXElement> subset = con[i].generate(match, ind);
  			Set<BioPAXElement> copy = new HashSet<BioPAXElement>(subset);
  
  			copy.removeAll(gen);
  			gen.removeAll(subset);
  			gen.addAll(copy);
  		}
  		return gen;
  	}
docs: Gets xor of the generated elements by the member constraints.
  @param match match to process
  @param ind mapped indices
  @return satisfying elements