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From: Dr Engelbert Buxbaum <engelbert_buxbaum@hotmail.com>
Newsgroups: comp.text.tex
Subject: Re: Double harpoons?
Date: Sun, 8 Sep 2024 17:13:34 +0200
Organization: private
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In article <vbehvm$p6bk$1@dont-email.me>, dieterhansbritz@gmail.com 
says...
> 
> I want to write a reversible chemial reaction using
> what I call double harpoons, but they don't seem to
> exist in LaTeX. Or do they? Using \longdoublearrows
> doesn't quite make it.

You can use the chemarrow package, it provides (amongst others) the 
\rightleftharpoons and \autorightleftharpoons{}{} commands. In the 
latter command, the length of the harpoons is adjusted to the text above 
and below them.

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