%% 
%%  The LaTeX Graphics Companion, 2ed (first printing May 2007)
%% 
%%  Example 8-4-5 on page 557.
%% 
%%  Copyright (C) 2007 Michel Goossens, Frank Mittelbach, Denis Roegel, Sebastian Rahtz, Herbert Vo\ss 
%% 
%%  It may be distributed and/or modified under the conditions
%%  of the LaTeX Project Public License, either version 1.3
%%  of this license or (at your option) any later version.
%% 
%%  See http://www.latex-project.org/lppl.txt for details.
%% 

\documentclass{ttctexa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{207.83385pt}

\StartShownPreambleCommands
\usepackage{feyn,slashed}
\StopShownPreambleCommands
\begin{document}
$  \feyn{\vertexlabel^a
     !{fA}p \vertexlabel^b}
   = \displaystyle
     \frac{i\delta^{ab}}{\slashed{p}-m_0} $
\end{document}