Notation: how to denote m-th element of a subsequence $x_{n_k}$ Sorry for probably stupid question, but I was not able to find an answer online. I want to denote m-th element of a subsequence $x_{n_k}$ while still showing that it is subsequence $x_{n_k}$. Is there any notation for this - some sort of $(x_{n_k})_m$ or $\{x_{n_k}\}_m$ or something like that?

If $n_1,n_2,n_3,\dotsc$ is a strictly increasing sequence of positive integers, then $x_{n_1},x_{n_2},x_{n_3},\dotsc=(x_{n_k})$ is a subsequence of $x_1,x_2,x_3,\dotsc=(x_n)$. The $m$th term of $(x_{n_k})$ is denoted $x_{n_m}$.
