directedGraph.addNode(node4);
directedGraph.addNode(node5);
directedGraph.addNode(node6);
directedGraph.addNode(node7);
directedGraph.addNode(node8);
directedGraph.addNode(node9);
Edge edge12 = graphModel.factory().newEdge(node1, node2);
Edge edge23 = graphModel.factory().newEdge(node2, node3);
Edge edge45 = graphModel.factory().newEdge(node4, node5);
Edge edge56 = graphModel.factory().newEdge(node5, node6);
Edge edge64 = graphModel.factory().newEdge(node6, node4);