ispis1:-izmedju(I,1,50),izmedju(J,3,20),K is I+J,K<20,
        write(I),write(','),write(J),nl,fail.
ispis1.

izmedju(X,X,Y):-X=<Y.
izmedju(X,Y,Z):-Y1 is Y+1,Y1=<Z,
                    izmedju(X,Y1,Z).