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I have a command that has been floating around in my standard preamble for a while:

\newcommand{\xeq}[1]{\stackrel{\;#1}{\cleaders\hbox{=\!}\hfill}\:}

It is meant to mimic the AMS-LaTeX extendible arrow symbols \xleftarrow and \xrightarrow.

It's not perfect for two reasons:

  1. It does not take the optional lower argument like the AMS \xrightarrow[down]{up}
  2. The overlap of the constituent equals signs is slightly visible.

Does anyone have a better command or know of a package with such a command?

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2 Answers 2

up vote 17 down vote accepted

I think you can more or less copy the definitions from amsmath.sty:

\documentclass{minimal}

\usepackage{amsmath}

\makeatletter
\newcommand*{\Relbarfill@}{\arrowfill@\Relbar\Relbar\Relbar}
\newcommand*{\xeq}[2][]{\ext@arrow 0055\Relbarfill@{#1}{#2}}
\makeatother

\begin{document}

$a \xeq[uuuuu]{vvv} b$

\end{document}
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Thanks, that works well. –  Simon Nov 2 '10 at 10:25

The extarrows package provides \xlongequal[below]{above}.

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