# label double arrows in both directions

How can I do something like this

$L_1 \xrightarrow[\alpha]{\xleftarrow{\gamma}}L_2$


where both arrows are of the same length?

• Is $L_1 \xleftrightharpoons[\gamma]{\alpha} L_2$ acceptable? (might need the mathtools package instead of amsmath) – Henri Menke Aug 3 '16 at 11:38
• @HenriMenke Good call, but unfortunately not in this particular case. I'm trying to get that into Freeplane which - unfortuantely - does not come with mathtools (or at least I have not yet found an option that would allow me to use xleftrightharpoons). – User1291 Aug 3 '16 at 12:05

The excellent Mathmode document explains how to make extensible arrows of all kinds (§38; pp.78-79). Here is an xleftrightarrow:

\documentclass{article}
\usepackage{mathtools, amssymb}

\makeatletter
\newcommand\xlongleftrightarrow[2][]{%
\ext@arrow 0059{\longleftrightarrowfill@}{#1}{#2}%
}
\def\longleftrightarrowfill@{%
\arrowfill@ ← \relbar → }
\makeatother

\begin{document}

\begin{equation*}