%% The LaTeX Graphics Companion, 2ed (first printing May 2007)

%%
%% 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}