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Would you guys help me design an integral symbol with the \infty symbol inscribed through it and aligned correctly with the slant of the integral symbol? I tried using

\DeclareMathOperator*{\loopint}{\begingroup \displaystyle \unitlength 1pt
 \int\mkern-8.9mu\begin{picture}(0,3)\put(-4.7,3){$\circ$}\end{picture}
 \hspace{-5.3pt}\raisebox{-1pt}{\displaystyle$\circ$}\mkern2mu\endgroup}

as you can see, rather than the infinity symbol, it just uses two circles which don't look professional in my opinion and also my latex editor give me an error that I have a missing $ in it which I cannot determine where.

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Thanks for providing what you had attemtped, but please keep in mind that instead of code snippets, it is always best to compose a compilable MWE including the \documentclass and the appropriate packages so that those trying to help don't have to recreate it. –  Peter Grill Nov 25 '11 at 16:59
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2 Answers

up vote 8 down vote accepted

You can use \Xint defined below to build your own integral signs. Using \Xint{\infty} will place \infty on the integral sign. If you want a rotated symbol you can use \rotatebox from the graphicx package which is what the \Rinfty does. So using \Xint{\Rinfty} generates the second symbol:

enter image description here

\documentclass{standalone}
\usepackage{amsmath}
\usepackage{graphicx}

\def\Xint#1{\mathchoice%
{\XXint\displaystyle\textstyle{#1}}% 
{\XXint\textstyle\scriptstyle{#1}}% 
{\XXint\scriptstyle\scriptscriptstyle{#1}}% 
{\XXint\scriptscriptstyle\scriptscriptstyle{#1}}% 
\!\int}%
\def\XXint#1#2#3{{\setbox0=\hbox{$#1{#2#3}{\int}$}%
\vcenter{\hbox{$#2#3$}}\kern-.5\wd0}}%

\newcommand{\Rinfty}{\rotatebox{77}{$\infty$}\hspace{0.6em}}%

\begin{document}
\[ \Xint{\infty} f(x) \qquad \Xint{\Rinfty} f(x)\]
\end{document}

As pointed out by AlanMunn, the original code is due to Donald Aresneau (posted in comp.text.tex in 1991) and appears in the UK TeX FAQ and also in Scott Pakin's Comprehensive LaTeX Symbols Guide (which credits the FAQ), and in Herbert Voss's comprehensive review of mathematics in (La)TeX.

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Ok, I understand the first post and will include a complet document the next time. However, that's not how I wish the infinity symbol to be aligned rather I'd like it aligned vertical with the same slant as the integral sign. Maybe I can study the code above however and get it rotated correctly. –  Jack Nov 25 '11 at 17:52
    
@Jack: So you want the \infty rotated? –  Peter Grill Nov 25 '11 at 17:59
    
Also, note if I just use an "8" in the code above, the font has a smaller top circle than the bottom circle which doesn't look professional when it's through the integral sign and also using the code above, it's not aligned perfectly with the slant of the integral sign. –  Jack Nov 25 '11 at 18:02
    
Yes, I'd like it rotated say, from the symbol here, around 85 degrees so that it's aligned perfectly with the integral sign. –  Jack Nov 25 '11 at 18:04
    
@Jake: Have provided an updated solution which also provides a version that places the rotated symbol. –  Peter Grill Nov 25 '11 at 18:21
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if you need it only in one size:

\documentclass{article}
\usepackage{mathtools}
\begin{document}
\[ \mathrlap{\mkern3mu\infty}\int f(x)\]
\end{document}

enter image description here

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