(documentationKappaFnEnglishLanguage "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.")