:- object(natural,
extends(integer)).
:- info([
version is 1.0,
author is 'Paulo Moura',
date is 2000/7/24,
comment is 'Natural numbers data type predicates.']).
between(Lower, Upper, Integer) :-
integer(Lower),
Lower > 0,
^^between(Lower, Upper, Integer).
valid(Natural) :-
integer(Natural),
Natural > 0.
:- end_object.
