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Is it possible to stack three relations or symbols ontop of one another? Specifically I would like to stack three symbols, R, \rightleftarrows and L in order to define a pair of adjoint functors $R:C\to D$ and $C\gets D:L$.

Also, is there a \rightleftarrow with long arrows? EDIT I actually meant to ask wether there is a version of \rightleftarrows with long arrows.

I'm not a regular user, so I don't know how to format my question adequately, could someone convert what's inside the dollar so that it appears as latex please?

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1  
For the second question, you have \longleftrightarrow. Can you please elaborate on how should the symbols be stacked? Do you have an image of the desired result? –  Gonzalo Medina Jan 13 '13 at 0:59
    
@GonzaloMedina Thanks for the command. I would like to have the R$ sit ontop of the leftrightarrow and the L to be below the longrightarrow. Similarly to when one writes \stackrel{def}{=} where the def sits atop the equality, I want the R to be where the def is in my example, and the L should be at the same place but below the equality sign. –  Olivier Bégassat Jan 13 '13 at 1:04
    
mathtools provides \xleftrightarrow[under]{over}. May be that's what you are looking for. –  Manuel Jan 13 '13 at 1:09

2 Answers 2

up vote 10 down vote accepted
\documentclass{article}
\usepackage{mathtools,amssymb}

\begin{document}
\[
x \mathrel{\substack{R\\\rightleftarrows\\ L}} y
\]

\[
x \mathrel{\substack{R\\\longleftrightarrow\\L}} y
\]
\end{document}

enter image description here

Edit:

Some hack wrote in a hurry to make long version of \rightleftarrows:

\documentclass{article}
\usepackage{mathtools,amssymb}
\newcommand{\myrightleftarrows}{\mathrel{\substack{\longrightarrow \\[-.6ex] \longleftarrow}}}

\begin{document}

\[
x \mathrel{\substack{R\\\myrightleftarrows\\L}}  y
\]
%
\[
x \mathrel{\substack{R\\\rightleftarrows\\ L}} y
\]
\end{document}

enter image description here

Hope this will get you started :-)

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Thank you very much, this did it for me! –  Olivier Bégassat Jan 13 '13 at 1:16
    
Do you know if I can get a long version of the \rightleftarrows somehow? –  Olivier Bégassat Jan 13 '13 at 1:20
    
Are you writing the code yourself? I'm currently using the code for a blogpost edited with wordpress, will I be able to use it in this environment? I'll definitely use it further down the line on a proper Latex compiler, just so you know your efforts will not be wasted :) –  Olivier Bégassat Jan 13 '13 at 1:27
    
That is fantastic :D thank you very much Harish Kumar! –  Olivier Bégassat Jan 13 '13 at 1:35

The mathtools package offers you \xleftrightarrow[<above>]{<below>}; for the second question, standard LaTeX has \longleftrightarrow:

\documentclass{article}
\usepackage{mathtools}

\begin{document}

$\longleftrightarrow\qquad\xleftrightarrow[L\,]{R\,}$

\end{document}

enter image description here

share|improve this answer
    
Thank you very much for your answer, I tried using your formula but it didn't work for some reason, maybe it's because I'm using wordpress to write latex. –  Olivier Bégassat Jan 13 '13 at 1:17

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