code: public WeightedGraph subgraph(Set<Integer> vertices) {
          // Get a subgraph from the parent graph (which is just a Graph) and then
          // wrap it with an adaptor to fulfill the WeightedGraph API
          Graph<WeightedEdge> g = super.subgraph(vertices);
          return new SubgraphAdaptor(g);
      }
docs: {@inheritDoc}