# Double arrow and variable on top [duplicate]

How to create a double arrow line with a variable on its top. Something like this.

## marked as duplicate by flav, user36296, Stefan Pinnow, Troy, TeXnicianSep 6 '18 at 14:55

Try package mathtools

\documentclass{article}
\usepackage{mathtools}
\begin{document}

$\xleftrightarrow[\text{world}]{\text{hello}}$

\end{document}

• instead \xleftrightarrow... according to op question should be \xLeftrightarrow ... – Zarko Sep 6 '18 at 14:15
• @Zarko Really? Doesn't double just mean (here) that there should be arrow heads on both sides? – marmot Sep 6 '18 at 14:16
• @marmot, hm, you are probably right ... question is not very clear to me :-( – Zarko Sep 6 '18 at 14:18
• @Zarko, I agree the question is maybe unclear but I tried the closest match to the picture :) – BambOo Sep 6 '18 at 14:32

With \overset:

\documentclass[border=2mm]{standalone}

\usepackage[]{amsmath}

\begin{document}
$\overset{n_S^i}{\leftrightarrow}$
\end{document}