code: @Override
      public Iterable<GraphEdge<V, E>> edges() {
          return F.map(vedges(), new Function<Map.Entry<V, GraphEdge<V, E>>, GraphEdge<V, E>>() {
              @Override
              public GraphEdge<V, E> apply(Map.Entry<V, GraphEdge<V, E>> entry) {
                  return entry.getValue();
              }
          });
      }
docs: Returns a list of the edges in the graph.
  @return edges of the graph.