%query: int(i,i,o). /* from Steinbach, 1995 */ intlist([],[]). intlist([X|XS],[s(X)|YS]) :- intlist(XS,YS). int(0,0,[0]). int(0,s(Y),[0|XS]) :- int(s(0),s(Y),XS). int(s(X),0,[]). int(s(X),s(Y),XS) :- int(X,Y,ZS), intlist(ZS,XS).