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

:- table p/0, q/0, r/0.

p :- tnot(q), tnot(r), p.
q :- tnot(q), tnot(r), p.
r :- tnot(q), p, tnot(r).
p :- tnot(q), tnot(r).

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

test :- q, fail.
test :- ( p ->	( tnot(p) -> writeln('p is undefined (OK)')
		; writeln('p is true') )
	; writeln('p is false') ),
        ( q ->  ( tnot(q) -> writeln('q is undefined (OK)')
		; writeln('q is true') )
	; writeln('q is false') ),
	( r ->  ( tnot(r) -> writeln('r is undefined (OK)')
		; writeln('r is true') )
	; writeln('r is false') ).