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