(
    (rel 
        (tuple 
            (
                (No_a int) 
                (No_b int)))) 
    (
        (1 1) 
        (1 2) 
        (2 1) 
        (2 2) 
        (1 3) 
        (2 3) 
        (3 1) 
        (3 2) 
        (3 3) 
        (1 4) 
        (2 4) 
        (3 4)))