%% 
%%  Example 03-03-4 
%%  Copyright (C) 2016 Herbert Voss
%% 
%% ==== 
% Show page(s) 1
%% 
%% 
\documentclass[]{screxa}
\pagestyle{empty}
\setlength\textwidth{134.31393pt}

%StartShownPreambleCommands

%StopShownPreambleCommands
\begin{document}
$a\atopwithdelims() b$     \\[8pt]
${n \atopwithdelims() k}
  = {n!\above1pt k!(n-k)!}$\\[8pt]
$\displaystyle{a\atopwithdelims\{. b}$
\end{document}
