# Error using \lrtimes

I am trying to use a symbol mapped by the tag \lrtimes in Math mode, but I am getting error. Here is what I am doing.

\begin{align*}
Sys_1 \stackrel{\text{\tiny def}}{=} (Appl \parallel Appl) \lrtimes  WS
\end{align*}


The \stackrel{\text{\tiny def}}{=} is a latex code for 'is defined as' operator which works fine in my other formulas.

The log message(from texmaker) reads as below:

! Undefined control sequence. ...}{=} (Appl \parallel Appl) \lrtimes WS l.69 \end{align*} The control sequence at the end of the top line of your error message was never \def'ed.

What is wrong in this case?

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While code snippets are useful in explanations, it is always best to compose a fully compilable MWE that illustrates the problem including the \documentclass and the appropriate packages so that those trying to help don't have to recreate it. –  Peter Grill Nov 30 '12 at 5:23
Ya sure, i agree –  Shafi Nov 30 '12 at 5:39
the name \bowtie also represents the same symbol, and it's already present in latex. –  barbara beeton Nov 30 '12 at 13:52

To use \lrtimes you need \usepackage{pxfonts} in the preamble:

## Code:

\documentclass{article}
\usepackage{amsmath}
\usepackage{pxfonts}
\begin{document}
\begin{align*}
Sys_1 \stackrel{\text{\tiny def}}{=} (Appl \parallel Appl) \lrtimes  WS
\end{align*}
\end{document}

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Thanks for the answer. The reason for the error is that pxfonts.sty file is missing. –  Shafi Nov 30 '12 at 5:34
One should note that this globally changes the document font. –  egreg Nov 30 '12 at 7:51