Following the question in Can we have x with tilde on top?
Basically, i want to have vector lenght like this
\documentclass{article}
\usepackage{amsmath}
\usepackage{amssymb}
\begin{document}
$\| \tilde{x} \| $
\end{document}
The output is:
But how to have another tilde at the bottom of X?




$\| \undertilde{\widetilde{x}} \|$,$\| \undertilde\widetilde{x} \|$. Even$\undertilde{x}$also not working. – aan Jan 13 '20 at 22:17