# How to include contraction symbols in LaTeX

1. Feb 6, 2009

### nrqed

I apologize, I know this is not a QM question per se but I think I am more likely to find someone who could answer this here.

I'd like to know (or rather, be reminded of) how to draw contraction symbols in LaTeX (or TeX). I mean the symbol we use to show how two fields are "paired up" when we do perturbation theory in QFT. You know what I mean: a line that goes a bit down (or up) from a field, runs across horizontally to the second field and then goes up again (or down again).
I used to have a way to do that but when my work computer was upgraded I lost those files.

Patrick

2. Feb 6, 2009

3. Feb 6, 2009

### nrqed

4. Oct 21, 2011

I also have the same doubt, but when I tried the way it is given in the CTAN package, and tried to compile the latex document I got the error
! Undefined control sequence.
l.27 \contraction
[2ex]{}{\phi_1}{\phi_2\phi_3}{\phi_4}
?
! Undefined control sequence.
l.28 \contraction
{\phi_1}{\phi_2}{}{\phi_3}
?

I also used their instruction generated the simplewick.sty file by latex simplewick.ins and placed it in the same directory as my original .tex fle but still the error persisted.
Is there anything else also I need to do like putting in some macros?

5. Jun 24, 2012

### Stefan_K

\contraction works fine for me with simplewick.sty, placing the style file in the same same directory should work. Perhaps you forgot \usepackage. This example is compilable:

Code (Text):
\documentclass{article}
\usepackage{simplewick}
\begin{document}
$\contraction[2ex]{}{\phi_1}{\phi_2\phi_3}{\phi_4}$
\end{document}
Stefan