%% 
%%  Example 02-11-2 
%%  Copyright (C) 2016 Herbert Voss
%% 
%% ==== 
% Show page(s) 1
%% 
%% 
\documentclass[]{screxa}
\pagestyle{empty}
\setlength\textwidth{158.31393pt}
\setlength\parindent{0pt}
\usepackage[T1]{fontenc}
\usepackage{kpfonts}
%StartShownPreambleCommands
\usepackage{amsmath}
%StopShownPreambleCommands
\begin{document}
\[
  X = \sum_{1\le i\le j\le n}X_{ij}
\]
\end{document}
