The command "\Perp" is in which package?

Question

X \Perp Y \mid Z

produces

But I don't know this command is in which package.

Answer 1

txfonts or pxfonts.

\documentclass{article}
\usepackage{txfonts}
% \usepackage{pxfonts}
\begin{document}
$X \Perp Y \mid Z$
\end{document}

---

Or you can declare symbol only for \Perp.

\documentclass{article}
\usepackage{bm}
\DeclareSymbolFont{symbolsC}{U}{txsyc}{m}{n}
\SetSymbolFont{symbolsC}{bold}{U}{txsyc}{bx}{n}
% \DeclareSymbolFont{symbolsC}{U}{pxsyc}{m}{n}
% \SetSymbolFont{symbolsC}{bold}{U}{pxsyc}{bx}{n}
\DeclareMathSymbol{\Perp}{\mathrel}{symbolsC}{121}
\begin{document}
$X \Perp Y \mid Z$
$\bm{X \Perp Y \mid Z}$
\end{document}