%% 
%%  Der Mathematiksatz mit LaTeX, 1. Auflage 2009
%% 
%%  Example 1-0-1 on page 4.
%% 
%%  Copyright (C) 2009 Herbert Voss
%% 
%%  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{355.65944pt}
\setlength\parindent{0pt}
\setcounter{equation}{0}
\renewcommand\theequation{1.\arabic{equation}}
\StartShownPreambleCommands
\usepackage{amsmath,esint}
\newcommand*\diff{\mathop{}\!\mathrm{d}}
\StopShownPreambleCommands
\begin{document}
\def\Q#1#2{\frac{\partial #1}{\partial #2}}
\begin{align}
\underset{{\mathcal{G}\quad}}\iiint\!\left[u\nabla^{2}v-v\nabla^{2}u\right]\diff^{3}V
        =\underset{\mathcal{S}\quad}\oiint\left(u\Q{v}{n}-v\Q{u}{n}\right)\diff^{2}A
\end{align}
\end{document}