I want to type k$\in$I as a subscript of \{$f_k$\} but am having trouble with

$\{$$f_k$$\}_{k$$\in$$ I}$

How should this be done?

  • Welcome to TeX.SX! Your main error is to enter and exit from math mode: $k\in I$ is the correct input; for the subscript, $\{f_k\}_{k\in I}$
    – egreg
    Commented Nov 25, 2015 at 7:46

1 Answer 1


Your error is going in and out of math mode: formulas should be typed as a single entity.

$\{f_k\}_{k\in I}$

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .