Human possess two nonverbal systems of representing numbers : the first represents numbers in an approximate fashion, and the second one conveys information about small numbers. Conception of exact large numbers has therefore been thought to arise from the manipulation of exact numerical symbols. We focuss on two fundamental properties of exact numbers as prerequesites to the concept of EXACT NUMBERS : The fact that all numbers can be generated by a successor function and the fact that equality between numbers can defined in an exact fashion.