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This professor is using this symbol to denote the input space.

enter image description here

an X with bars at the top and bottom, is there a latex font correspond to the symbol?

I've tried Detexify,

enter image description here

didn't get any luck.

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  • You could try detexify.kirelabs.org/classify.html to draw your symbol. I did it, but was not able to get any hints. Good luck!
    – Jan
    Dec 14, 2019 at 8:37
  • 1
    That’s not a special symbol, but just an X. I’ve seen several people writing it like that on the blackboard, probably for distinguishing it from \times.
    – egreg
    Dec 14, 2019 at 8:59
  • @egreg So, is there a latex symbol to render that in computer?
    – JJJohn
    Dec 14, 2019 at 9:04
  • @JJJohn Not sure what you mean: you render it with X.
    – egreg
    Dec 14, 2019 at 9:33
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    By the way, if you notice, in the last line the X has no bars and it represents exactly the same quantity.
    – egreg
    Mar 13, 2020 at 23:16

2 Answers 2

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Using the package romanbar (\usepackage{romanbar}), it is possible to obtain an X with bars at the top and bottom. I hope that the symbol is good for you.

\documentclass[12pt,a4paper]{article}
\usepackage{romanbar}
\usepackage{mathtools}
\DeclarePairedDelimiter\abs{\lvert}{\rvert}
\newcommand\Romanx{\mathord{\Romanbar{10}}}
\begin{document}
\Romanbar{10}, \verb|It is used in text-mode|

\[\abs{\Romanx}=2^{1000}, \verb|It is used in math-mode|\]
\end{document}

enter image description here

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There is no such symbol on the blackboard. It's simply an uppercase “X” that some people adorn on the blackboard with bars perhaps in order to distinguish it from ⨉.

If you look closely, the same symbol for the cardinality of X is used at the exponent of 2, and the X has no ornament.

Nothing special: it's just an X.

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