%% 
%%  The LaTeX Graphics Companion, 2ed (first printing May 2007)
%% 
%%  Example 8-4-19 on page 571.
%% 
%%  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{348.0pt}
\AtEndDocument{\end{fmffile}}
  \AtBeginDocument{\begin{fmffile}{ftmp}}
\StartShownPreambleCommands
\usepackage{feynmp}
\StopShownPreambleCommands
\begin{document}
\begin{equation}
 \parbox{40mm}{%
  \begin{fmfgraph*}(100,90)
   \fmfleft{i}\fmfright{o}
   \fmf{photon}{i,v3}\fmf{photon}{v3,v1}
   \fmf{photon}{v4,v2}\fmf{photon}{v2,o}
   \fmf{fermion,left,tension=.3}{v1,v4,v1}
  \end{fmfgraph*}}
 =\frac{-i\eta^{\mu\alpha}}{q^2+i\epsilon}\left[\hspace*{-0.1cm}
 \parbox{30mm}{%
  \begin{fmfgraph*}(60,60)
   \fmfleft{i}\fmfright{o}
   \fmf{phantom}{i,v1}\fmf{phantom}{v2,o}
   \fmf{fermion,left,tension=.3}{v1,v2,v1}
   \fmfdotn{v}{2}
   \fmflabel{$\alpha$}{v1}\fmflabel{$\beta$}{v2}
  \end{fmfgraph*}}
 \hspace*{-1cm}\right]
 \frac{-i\eta^{\beta\nu}}{q^2+i\epsilon}\label{feyneq}
\end{equation}
\end{document}