Widecheck with hat does not work

Question

I defined new check from the internet, and re defined hat with widehat using amsmath. But this compiles somewhat strange. My MWE is as follows:

\documentclass{article}
\usepackage{amsmath}
\renewcommand{\hat}{\widehat}
%%widecheck
\DeclareFontFamily{U}{mathx}{}
\DeclareFontShape{U}{mathx}{m}{n}{<-> mathx10}{}
\DeclareSymbolFont{mathx}{U}{mathx}{m}{n}
\DeclareMathAccent{\widehat}{0}{mathx}{"70}
\DeclareMathAccent{\widecheck}{0}{mathx}{"71}
\renewcommand{\check}{\widecheck}
\begin{document}
$\check{\hat{f}(-\xi)}(-x)$
\end{document}

And this compiles like:

How can I resolve this issue? Thank you.