![双箭头和顶部的变量](https://linux22.com/image/382222/%E5%8F%8C%E7%AE%AD%E5%A4%B4%E5%92%8C%E9%A1%B6%E9%83%A8%E7%9A%84%E5%8F%98%E9%87%8F.png)
答案1
试用包mathtools
\documentclass{article}
\usepackage{mathtools}
\begin{document}
$\xleftrightarrow[\text{world}]{\text{hello}}$
\end{document}
试用包mathtools
\documentclass{article}
\usepackage{mathtools}
\begin{document}
$\xleftrightarrow[\text{world}]{\text{hello}}$
\end{document}