%------------------------------------------------------------------------
% Program that used to give wrong results.
%
% Model T = {q,r}, F = {p}, U = {}.
%------------------------------------------------------------------------

:- dynamic rule/2.

:- table interp_g/1, interp/1.

interp([]).
interp([G|Gs]) :- interp_g(G),interp(Gs).
interp_g(tnot(G)) :- tnot(interp_g(G)).
interp_g(G) :- rule(G,B),interp(B).

%-------------------------------------------------------------------------------

test :- new_program, query(Goal), interp_g(Goal), fail.
test :- ( interp_g(p) -> ( tnot(interp_g(p)) -> writeln('i(p) is undefined')
			 ; writeln('i(p) is true') )
	; writeln('i(p) is false (OK)') ),
        ( interp_g(q) -> ( tnot(interp_g(q)) -> writeln('i(q) is undefined')
			 ; writeln('i(q) is true (OK)') )
	; writeln('i(q) is false') ),
	( interp_g(r) -> ( tnot(interp_g(r)) -> writeln('i(r) is undefined')
			 ; writeln('i(r) is true (OK)') )
	; writeln('i(r) is false') ), fail.
test :- writeln('Program interp2 finished execution...').

%-------------------------------------------------------------------------------

new_program :- cleanup, assert(query(r)),
	assert(rule(p, [tnot(q),p])),
	assert(rule(r, [tnot(p),q])),
	assert(rule(q, [tnot(p)])).

cleanup :- retractall(query(_)), retractall(rule(_,_)), abolish_all_tables.