test :- a, fail.
test :-
	( a -> writeln('a is true') ; writeln('a is false') ),
	( b -> writeln('b is true') ; writeln('b is false') ),
	( c -> writeln('c is true') ; writeln('c is false') ),
	( d -> writeln('d is true') ; writeln('d is false') ),
	( e -> writeln('e is true') ; writeln('e is false') ),
	( f -> writeln('f is true') ; writeln('f is false') ).

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


:- table a/0, b/0, c/0, d/0, e/0, f/0.

a :- b, d.

b :- c.
b.

c :- b, f, c.

d :- tnot(e).
d :- c.
d :- tnot(c).

e :- c.

f :- b.