pythagorean_triples(X, Y, Z) :-
       list_of_k_integers(3, X:Y:Z:nil),
       plus(2, Something, X), /* X >= 2 */
       plus(X, SomethingElse, Y), /* Y >= X */
       times(X,X,Xsquared),
       times(Y,Y,Ysquared),
       times(Z,Z,Zsquared),
       plus(Xsquared,Ysquared,Zsquared).

sum_of_four_squares(S, W, X, Y, Z) :-
       list_of_k_integers(4, W:X:Y:Z:nil),
       times(W,W,Wsquared),
       times(X,X,Xsquared),
       times(Y,Y,Ysquared),
       times(Z,Z,Zsquared),
       plus(Wsquared, Xsquared, FirstSubTotal),
       plus(Ysquared,Zsquared, SecondSubTotal),
       plus(FirstSubTotal, SecondSubTotal, S).