begin:
    graph x;
    print(x);
    graph y={1:[1,2], 2:[3,1,4], 3:[4], 4:[]};
    print(y);
    graph z=y;
    print(z);
    print_matrix_d(y);
    print_matrix_u(y);
    graph w1 = {1:[4], 4:[10], 10:[1,4]};
    print(w1);
    graph w2 = w1 + y;
    print(w2);
    w2 = w1 + {2:[1], 1:[1,2]};
    print(w2);
    graph w3 = w1*y;
    print(w3);
    graph w4 = ~w3;
    print(w4);
    delete w1 4;
    print(w1);
    w2[1];
end