Stacked left and right arrows

Question

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.

Answer 1

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}

Answer 2

\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}
\newcommand{\lrarrow}{\mathrel{\ensurestackMath{\ThisStyle{\renewcommand\stacktype{L}%
  \stackanchor[3\LMpt]{\SavedStyle\,\,\rightarrow}{\SavedStyle\leftarrow\,\,}}}}}
\begin{document}\Huge
$A\lrarrow B_{\lrarrow}$


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