# How to place symbols on top of each other (not \overset, \underset)?

I tried to set two symbols on top of each other via:

\begin{align*}
\Rightarrow\atop\nLeftarrow
\end{align*}


How can I reduce the space between the symbols? \overset etc. is what I normally use, but that reduces the size of one of the symbols and I would like them to be of the same size.

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Use the \genfrac command from the amsmath package.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
$\genfrac{}{}{0pt}{0}{\Rightarrow}{\Leftarrow}$
\end{document}


Another possibility is to use an array environment. In this case an optional argument to the \\ macro allows you to manually adjust the vertical spacing.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
$\begin{array}{c} \displaystyle\Rightarrow \\[-5pt] \displaystyle\Leftarrow \end{array}$
\end{document}

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Thanks, Ian, the array solved it! –  Marius Hofert Jul 28 '12 at 14:02