# How to write text above and below \iff so that it works with breqn?

breqn makes the following code not work in one of my latex files, and I am not sure how to code it differently so that it works with breqn loaded as I need this package for other things. Here is the problem

\documentclass[11pt]{scrbook}%ext
\usepackage{amsmath}
\usepackage{breqn}
\begin{document}
$A \overset{Forward}{\underset{inverse}{\iff}} B$
\end{document}


This gives the error

Undefined control sequence. A \overset{Forward}{\underset{inverse}{\iff}}


Removing breqn, it compiles ok lualatex foo.tex

This is what I tried

  A  \iff^{Forward}_{inverse} B
A  \overset{Forward}{\iff}_{inverse} B


And I give up. I am not good at Latex.

Is there a different way to code this that give similar result, but also when breqn is loaded?

TL 2016

Instead of \iff, you can use an extensible arrow from mathtools (which loads amsmath, and should therefore be compatible with your example):
\documentclass{article}
$A \overset{Forward}{\underset{inverse}{\iff}} B \qquad A \xLeftrightarrow[\text{inverse}]{\text{forward}} B$