# \notimplies command error with breqn package

I'm trying to use this answer's "not imply" symbol. However I get the error:

Argument of \mathpalette has an extra }


Here is a MWE:

\documentclass{article}

\usepackage{amsmath}
\usepackage{breqn}

\newcommand{\notimplies}{%
\mathrel{{\ooalign{\hidewidth$\not\phantom{=}$\hidewidth\cr$\implies$}}}}

\begin{document}
$x\notimplies y$
\end{document}


The problem seems to be with the breqn package.

You betcha! breqn redefines \not to have an argument and so it finds \phantom, which is wrong in this context.
Add a couple of braces; even without breqn the result will be the same.
\newcommand{\notimplies}{%
\ooalign{\hidewidth$\not{\phantom{=}}$\hidewidth\cr$\implies$}

I removed the additional one around the \ooalign that serve no purpose, because \mathrel{...} forms a group.