%% 
%%  A DANTE-Edition example
%% 
%%  Example 16-03-3 on page 237.
%% 
%%  Copyright (C) 2011 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.
%% 
%% 
%% ==== 
% Show page(s) 1
%% 
\documentclass[]{article}
\pagestyle{empty}
\setlength\textwidth{375.57637pt}
\setlength\parindent{0pt}

\usepackage{pstricks,pst-node}
\def\DefNodes#1#2{\rnode[tl]{#1-tl}{\rnode[tr]{#1-tr}{%
    \rnode[bl]{#1-bl}{\rnode[br]{#1-br}{#2}}}}}

\begin{document}
\LARGE\[ \frac{\DefNodes{A}{A_1}+\DefNodes{B}{B_1}+C_1}
         {\DefNodes{D}{D_1}+\DefNodes{E}{E_1}+\DefNodes{F}{F_1}} \]
\psccurve[linecolor=red,linestyle=dashed,fillstyle=hlines,hatchcolor=yellow]%
   (D-bl)(A-tl)(A-tr)([angle=-90,nodesep=0.1]B-bl)
   ([angle=-90,nodesep=0.1]B-br)(F-tr)(F-br)(F-bl)
   ([angle=90,nodesep=0.1]E-tr)([angle=90,nodesep=0.1]E-tl)(D-br)(D-bl)
\end{document}