/* File:      pre_image.P
** Author(s): Baoqiu Cui
**
** $Id: pre_image.P,v 1.1 1999-11-04 23:04:29 cbaoqiu Exp $
*/

:- import put_attributes/2, get_attributes/3 from machine.
:- import attv_unify/2 from machine.

test :-
	put_attributes(X, v(a)),
	put_attributes(Y, v(b)),
	p(X,Y),
	write('X-Y = '), writeln(X-Y),
	fail.

test :- writeln('-------------------------').
	
verify_attributes(Var, Value) :-
	attv_unify(Var, Value).

p(X,Y) :-
	X = 5,
	(q(Y); r(Y)).

q(6).
r(7).
