Limit is an important concept in mathematics. In mathematics, if a variable is infinitely close to a certain value, then this fixed value is called the limit of this variable.

Let |Xn| be an infinite sequence. If there is a constant a for any given positive number ε (no matter how small it is), there is always a positive integer n, so that when n >: all Xn, when n has the inequality | xn-a |.

1. Uniqueness: If the limit of the sequence exists, the limit value is unique, and the limit of its subsequence is equal to the limit of the original sequence; 2. Boundedness: If a sequence {xn} converges (has a limit), then this sequence {xn} must be bounded. However, if a series is bounded, it may not converge. For example, {xn}: 1,-1,-1, ... (-1) n+ 1, ... 3. Preservative number: If a series {xn} converges. 0 (or a