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A short warning at the beginning: I basicly know nothing about LaTeX, so please excuse my question. Google didn't help me.

I want to have a product sign analogously to $A \amalg B$. I tried $A \Pi B$, but as $\Pi$ isn't a binary operator, this does not look that good.

Can you help me? Thanks in advance!

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1  
You can try drawing the symbol at detexify; if it can find a match, it will tell you the command for the symbol and which package it's loaded with. –  ChrisS Jul 31 '13 at 9:00
    
Thanks. It just finds $\Pi$ as I expected. –  John Jul 31 '13 at 9:03

2 Answers 2

Use \mathbin to fix the spacing issue.

\documentclass{article}
\newcommand*\productop{\mathbin{\Pi}}

\begin{document}
\[ a \amalg b \qquad a \productop b\]
\end{document}

enter image description here

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Thank you! That was exactly what I was looking for. –  John Jul 31 '13 at 9:11

Another solution is to rotate 180° the symbol \amalg (requires graphicx) to get exactly the same symbol upside down:

\documentclass{article}
\usepackage{graphicx}

\newcommand{\invamalg}{\mathbin{\rotatebox[origin=c]{180}{$\amalg$}}}

\begin{document}
\[ A \amalg B \qquad A \invamalg B\]
\end{document}

enter image description here

To get a size changing symbol you can load the amsmath package and modify the \newcommand line as follows (thanks to egreg for the suggestion):

\newcommand{\invamalg}{\mathbin{\text{\rotatebox[origin=c]{180}{$\amalg$}}}}

In this way you can use the new defined command even in subscripts and superscripts. The following MWE

\documentclass{article}
\usepackage{amsmath}
\usepackage{graphicx}

\newcommand{\invamalg}{\mathbin{\text{\rotatebox[origin=c]{180}{$\amalg$}}}}

\begin{document}

\[
 A \invamalg B_{A \invamalg B_{A \invamalg B}}
\]

\[
 A \amalg B_{A \amalg B_{A \amalg B}}
\]

\end{document}

gives the result:

enter image description here

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Even better for my purposes. Thanks a lot. –  John Jul 31 '13 at 9:21
    
\amalg is slightly different from a reversed \Pi. You can get a size changing symbol by loading amsmath and putting \rotatebox[...]{180}{...} inside \text. –  egreg Jul 31 '13 at 9:29
    
With \mathchoice{\text{...}} you're typesetting the symbol sixteen times instead of the four with the \text method and the result is exactly the same (\text already does \mathchoice by itself). There's no need to load \mathtools in order to have \mathchoice, which is a primitive of TeX. –  egreg Jul 31 '13 at 11:57
    
@egreg I've deleted that solution. Thanks for pointing it out. –  karlkoeller Jul 31 '13 at 13:54

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