notation for the external set of all positive unlimited real numbers [duplicate]

Question

I couldn't find the notation for the external set of all positive unlimited real numbers. It's like the symbol of infinity with a slash over it I've tried \ninfty in fashion of \nequal but it didn't work you can find this notation in this book Nonstandard Analysis in Practice

Answer 1

Like this?

\documentclass{article}
\usepackage{stackengine} 

\begin{document}

$\stackMath\stackinset{c}{0pt}{c}{0pt}{/}{\infty}$

\end{document}