* networks. Example:
   *
   * <pre>{@code
   * static final ImmutableNetwork<City, Train> TRAIN_NETWORK =
   *     NetworkBuilder.undirected()
   *         .allowsParallelEdges(true)
   *         .<City, Train>immutable()
   *         .addEdge(PARIS, BRUSSELS, Thalys.trainNumber("1111"))
   *         .addEdge(PARIS, BRUSSELS, RegionalTrain.trainNumber("2222"))

   * networks. Example:
   *
   * <pre>{@code
   * static final ImmutableNetwork<City, Train> TRAIN_NETWORK =
   *     NetworkBuilder.undirected()
   *         .allowsParallelEdges(true)
   *         .<City, Train>immutable()
   *         .addEdge(PARIS, BRUSSELS, Thalys.trainNumber("1111"))
   *         .addEdge(PARIS, BRUSSELS, RegionalTrain.trainNumber("2222"))

   * graphs. Example:
   *
   * <pre>{@code
   * static final ImmutableValueGraph<City, Distance> CITY_ROAD_DISTANCE_GRAPH =
   *     ValueGraphBuilder.undirected()
   *         .<City, Distance>immutable()
   *         .putEdgeValue(PARIS, BERLIN, kilometers(1060))
   *         .putEdgeValue(PARIS, BRUSSELS, kilometers(317))

            doColumn("businessCategory");
        }

        public void columnCarLicense() {
            doColumn("carLicense");
        }

        public void columnCity() {
            doColumn("city");
        }

        public void columnDepartmentNumber() {
            doColumn("departmentNumber");
        }

        public void columnDescription() {
            doColumn("description");

   * graphs. Example:
   *
   * <pre>{@code
   * static final ImmutableValueGraph<City, Distance> CITY_ROAD_DISTANCE_GRAPH =
   *     ValueGraphBuilder.undirected()
   *         .<City, Distance>immutable()
   *         .putEdgeValue(PARIS, BERLIN, kilometers(1060))
   *         .putEdgeValue(PARIS, BRUSSELS, kilometers(317))