code: public Iterator<Map.Entry<G,Integer>> iterator() {
          List<Iterator<Map.Entry<G,Integer>>> iters = 
              new ArrayList<Iterator<Map.Entry<G,Integer>>>(orderAndSizeToGraphs.size());
          for (Map<G,Integer> m : orderAndSizeToGraphs.values())
              iters.add(m.entrySet().iterator());
          return new CombinedIterator<Map.Entry<G,Integer>>(iters);
      }
docs: {@inheritDoc}