}

    static void addEdge(Graph graph, String v1, String v2) throws CycleDetectedException {
        Vertex vx1 = graph.addVertex(v1);
        Vertex vx2 = graph.addVertex(v2);
        graph.addEdge(vx1, vx2);
    }

    static boolean hasEdge(Graph graph, String v1, String v2) {
        Vertex vx1 = graph.getVertex(v1);
        Vertex vx2 = graph.getVertex(v2);