Symbol manipulation

The power of a modern computer derives from its being more than an arithmetic calculator. It is, in fact, a general-purpose symbol-manipulating system. A symbol token is a pattern that can be compared by an information processing system with some other symbol token and judged equal with it or different from it. The basic test for equality of tokens incorporated in an information processing system determines the fundamental alphabet of symbols it is prepared to recognize and distinguish. A symbol, then, is a class of equal tokens with respect to this basic test.