% to read this file with standard Prolog, uncomment the next two lines:
:- op(1150,fx,function).
function(_).

:- function tak/4.
tak(X,Y,Z,A) :-
	X =< Y
        -> A=Z
	 ; ((X1 is X - 1),
            tak(X1,Y,Z,A1),
            (Y1 is Y - 1),
            tak(Y1,Z,X,A2),
            (Z1 is Z - 1),
            tak(Z1,X,Y,A3),
            tak(A1,A2,A3,A)).

goal0(R) :- tak(24,16,8,R).
goal1(R) :- tak(27,16,8,R).
goal2(R) :- tak(33,17,8,R).

main(R) :- goal1(R).