How to write ‎\leftrightarrow with a line below

Question

I would really appreciate if someone could tell me how I can ‎‎\leftrightarrow with a line below like this?

I tried ‎‎\leftrightarroweq but it didn't work.

Answer 1

You can build your own symbol:

\documentclass{article}
\usepackage{amsmath}

\makeatletter
\newcommand{\leftrightarroweq}{\mathrel{\mathpalette\leftrightarroweq@\relax}}
\newcommand{\leftrightarroweq@}[2]{%
  \vtop{
    \sbox\z@{$\m@th#1\leftrightarrow$}%
    \ialign{%
      \hfil##\hfil\cr
      \copy\z@\cr
      \noalign{\nointerlineskip\kern0.7\ht\z@}
      \makebox[\wd\z@][s]{$\m@th#1\relbar\hss\relbar$}\cr
      \noalign{\kern-0.7\ht\z@}
    }%
  }%
}
\makeatother

\begin{document}

$a \leftrightarroweq b \leftrightarrow c$

$\scriptstyle a \leftrightarroweq b \leftrightarrow c$

$\scriptscriptstyle a \leftrightarroweq b \leftrightarrow c$

\end{document}

Compare with what you get with

\documentclass{article}
\usepackage{amsmath}
\usepackage{stmaryrd}

\begin{document}

$a \leftrightarroweq b \leftrightarrow c$

$\scriptstyle a \leftrightarroweq b \leftrightarrow c$

$\scriptscriptstyle a \leftrightarroweq b \leftrightarrow c$

\end{document}

I don't think you want this.

Answer 2

The command \leftrightarroweq requires the package stmaryrd (or boisik). If you don't want to load all the glyphs, you can use the onlyoption:

\documentclass{article}

\usepackage[only,leftrightarroweq]{stmaryrd}

\begin{document}

$A\leftrightarroweq B$

\end{document}