The marriage certificates of the children always mention the death or not of their parents. In the most recent civil status records, the date and place of death are even mentioned. Similarly, the death certificates of the children make it possible to know whether their parents were deceased or not, but without more precision. Study calculus, the first step is to understand that the "limit" the necessity of introducing: because, the concept of algebra is people are familiar with, but, algebra is unable to process the concept of "unlimited". So in order to use algebraic processing to represent infinite quantities, the concept of "limit" is constructed. In the definition of "limit", we can see that this concept bypasses the problem of dividing a number by 0, and introduces a process with any small amount. Is to say, the divisor is not zero, so meaningful, at the same time, this process can take any small small, as long as meet the Δ range, less than the arbitrary small, we can say he limit to the number, you can think it is opportunistic, however, his practical proof, such a definition is more perfect, the possibility of giving the correct inference. The concept is successful