Then we subtract the initial number from the mirror number, or vice versa, depending on which is larger, and continue the process as long as possible(fig. l). In the second example(fig. 2), we begin with the number 896 and using its mirror number, proceed in the same way. We see in both examples that the sequence of differences stops after only a steps, that is, it comes to difference of a zero. The question then arises as to whether this happens merely by accident, because of our choice of numbers, or whether all such sequences of differences of three-digit with the latter is numbers will end zero. If true, how many steps are the least neces sary, and how many are the most necessary, until the process ends this way