This is very simple. This problem proved to be mathematical induction. Firstly, it is understood that n is the subscript of series, which represents the order of series, and n is a certain value of n. When n approaches infinity, there must be n>n. Nk is the subsequence of subsequence subscript of the original sequence extracted from the original sequence, and K represents the new subscript in this subsequence, which can also be understood as | xk |；; This makes it clear that k (capital) is a certain value of k, and when k approaches infinity, there must be k >；; K (capital) is established, that is, when k >; K, the number of series nk extracted from the original series will be greater than a certain n k (capital), and when k (capital) =N, the number of series nK extracted from the original series will be greater than n.

NN represents the nth value of the subsequence extracted from the original sequence. In the case of K=N, n in the new subsequence must be greater than =N in the original sequence.

Simple example:

Original series: x 1, x2, x3...xn, xn+ 1, xn+2, xn+3 ... xn+n.

Subseries: x3, x5, xn, xn+ 1...xn+n (represented by elements of the original sequence)

Xn 1, xn2, xn3, xn4, xn5, Xn6........xnk ... (expressed by subscripts)

Then in the subsequence, xn 1=x3, xn2=x5, xn3=xn. ........

Assuming that the original sequence has n elements and the subsequence also has n elements, when k> when k (capital) =N, is it uncertain whether n k is greater than or equal to n? Of course, there are cases where nN is greater than n.