[Tex/LaTex] Is it possible to typeset this double-X symbol

symbols

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I'm looking for this double-X symbol. Is this available in some package? If not, would it somehow be possible to recreate this symbol by creating a new symbol which consists of two Xs printed on top of each other?

Best Answer

You should define a macro for that symbol, say \XX that inserts a negative space between the two X's. This space should depend on where it's used inside math mode (using \mathchoice):

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\documentclass{article}

\usepackage{amsmath}

\newcommand{\XX}{% Space between XX varies depending on where it's used
  \mathchoice% https://tex.stackexchange.com/q/148740/5764
    {X\mskip-12.5mu X}% \displaystyle
    {X\mskip-12.5mu X}% \textstyle
    {X\mskip-12mu X}% \scriptstyle
    {X\mskip-11.5mu X}% \scriptscriptstyle
}

\begin{document}

\[
  \text{Var} \bigl( \hat{\beta} \,\vert\, \XX \bigr) \quad \XX^{\XX^{\XX}}
\]

\end{document}
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