A program solving geometric analogies

Source: The Art of Prolog

Program source code: analogy.pl

/*
   analogy(Pair1,Pair2,Answers) :-
	An analogy holds between the pairs of figures Pair1 and Pair2.
	The second element of Pair2 is one of the possible Answers.
*/
:- op(100,xfx,[is_to]).
 
analogy(A is_to B,C is_to X,Answers) :-
    match(A,B,Match),
    match(C,X,Match),
    member(X,Answers).
 
match(inside(Figure1,Figure2),inside(Figure2,Figure1),invert).
match(above(Figure1,Figure2),above(Figure2,Figure1),invert).
 
   /*  Testing and data		*/
 
:- op(40,xfx,[is_to]).
 
test_analogy(Name,X) :-
    figures(Name,A,B,C),
    answers(Name,Answers),
    analogy(A is_to B,C is_to X,Answers).
 
figures(test1,inside(square,triangle),inside(triangle,square),
					inside(circle,square)).
answers(test1,[inside(circle,triangle),inside(square,circle),
					inside(triangle,square)]).
 
%	Program 14.13: A program solving geometric analogies
% ?- test_analogy(test1,X).