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)))))))