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IN THE PAST SEVERAL YEARS, several papers1,2 have been written that have developed a description language that can be used to describe classes of objects. A class is a grouping of a number of objects such as all integral numbers, all five card poker hands, or all sentences generated by the rules of a given context free grammar. This description language is useful because all objects in a given class can be described using only one class description; also, many different classes can be described using this one description language. We shall use the word concept to mean the class description. Note that a concept describes a class of objects.
E. C. Milliken (Fri,) studied this question.