notes/school/di-ma/uebung/07/07_2_3.dot

graph {
    node [ shape="circle" ]
    {
        rank=same;
        1; 2;
        1 -- 2;
    }
    {
        rank=same;
        3; 4;
        3 -- 4;
    }
    1 -- 3;
    2 -- 4;
    1 -- 4;
}