}

  /** Returns a string representation of this network. */
  @Override
  public String toString() {
    return "isDirected: "
        + isDirected()
        + ", allowsParallelEdges: "
        + allowsParallelEdges()
        + ", allowsSelfLoops: "
        + allowsSelfLoops()
        + ", nodes: "
        + nodes()
        + ", edges: "
        + edgeIncidentNodesMap(this);
  }

  /**

    // In a directed graph, parallel edges cannot introduce a cycle in an acyclic graph.
    // However, in an undirected graph, any parallel edge induces a cycle in the graph.
    if (!network.isDirected()
        && network.allowsParallelEdges()
        && network.edges().size() > network.asGraph().edges().size()) {
      return true;
    }
    return hasCycle(network.asGraph());
  }

  /**