%------------------------------------------------------------------------
% Program for which non-trivial ANSWER COMPLETION is needed.
%------------------------------------------------------------------------

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

p :- p.
p :- q.

q :- p.
q :- tnot(s).

s :- tnot(r).
s :- p.

r :- tnot(s), r.

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

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