Stacked left and right arrows

Of all the arrows available, I can't seem to find something that looks like this:

Is there a reason for this? The \leftrightharpoons is the closest alternative. But I would rather have the arrows look like in the image above.

• See, e.g. \rightleftarrows in table 146 of the Comprehensive LaTeX symbols. – Schweinebacke May 8 '17 at 12:31
• @Schweinebacke None of the symbols listed is like that, as far as I can see. – egreg May 8 '17 at 12:36
• @Schweinebacke That document was awesome. Mathabx package got the symbol (page 71). – E. l4d3 May 8 '17 at 13:01
• There are six different versions of \leftrightarrows/\rightleftarrows listed in the comprehensive list, but none of them are identical to your image (the arrows are positioned a bit different, with the start of one arrow directly above/below the tip of the other). – Torbjørn T. May 8 '17 at 13:14

Here's a code for it:

\documentclass{article}
\usepackage{amsmath}

\makeatletter
\newcommand{\lrarrow}{\mathrel{\mathpalette\lrarrow@\relax}}
\newcommand{\lrarrow@}[2]{%
\vcenter{\hbox{\ooalign{%
$\m@th#1\mkern6mu\rightarrow$\cr
\noalign{\vskip1pt}
$\m@th#1\leftarrow\mkern6mu$\cr
}}}%
}
\makeatother

\begin{document}

$A\lrarrow B_{\lrarrow}$

\end{document}

\documentclass{article}
\usepackage{stackengine,scalerel}
\newcommand{\lrarrow}{\mathrel{\ensurestackMath{\ThisStyle{%
\stackanchor[\dimexpr-2.5pt-4\LMpt]{\SavedStyle\,\,\rightarrow}%
{\SavedStyle\leftarrow\,\,}}}}}
\begin{document}\Huge
$A\lrarrow B_{\lrarrow}$

$\scriptstyle A\lrarrow B_{\lrarrow}$
\end{document}

Alternately,

\documentclass{article}
\usepackage{stackengine,scalerel}
\stackanchor[3\LMpt]{\SavedStyle\,\,\rightarrow}{\SavedStyle\leftarrow\,\,}}}}}
\begin{document}\Huge
$A\lrarrow B_{\lrarrow}$

$\scriptstyle A\lrarrow B_{\lrarrow}$
\end{document}