| KappaFn | Formula | SymbolicString | Class | A class-forming operator that takes two  arguments:  a variable and a formula containing at least one unbound  occurrence of the variable.  The result of applying KappaFn to a  variable and a formula is the Class of things that satisfy the formula.   For example, we can denote the Class of prime numbers that are less  than 100 with the following expression:  (KappaFn ?NUMBER  (and (instance ?NUMBER PrimeNumber) (lessThan ?NUMBER 100))).  Note that  the use of this function is discouraged, since there is currently no  axiomatic support for it |   | BinaryFunction |