An real range is a class of real numbers specified by lower and upper bounds. Instances of an real-range are real numbers.
(<=> (Real-Range ?Class)
(And (Class ?Class)
(Subclass-Of ?Class Real-Number)
(Value-Cardinality ?Class R-Lower-Bound 1)
(Value-Cardinality ?Class R-Upper-Bound 1)
(Forall (?I)
(=> (Instance-Of ?I ?Class)
(And (=< (R-Lower-Bound ?Class) ?I)
(=< ?I (R-Upper-Bound ?Class)))))))