Suppose that for every natural number k {\displaystyle {}k} , a null sequence y k {\displaystyle {}y_{k}} is given, we denote the n {\displaystyle {}n} -th member of the k {\displaystyle {}k} -th sequence by y k n {\displaystyle {}y_{kn}} . Is the sequence z n {\displaystyle {}z_{n}} , whose n {\displaystyle {}n} -th member is defined by