%% 
%%  A DANTE-Edition example
%% 
%%  Example 06-00-24 on page 191.
%% 
%%  Copyright (C) 2010 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{201.70511pt}
\setlength\parindent{0pt}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}

\usepackage{array,slashbox,ragged2e}

\begin{document}
\renewcommand\arraystretch{1.6}
\begin{tabular}{|*{4}{>{%
  \Centering$}m{12mm}<{$}|}}\hline
\multicolumn{1}{|c|}{%
  \backslashbox{$v_n$}{$u_n$}}
  & \ell&+\infty&-\infty\\\hline
\ell'  &\ell+\ell'&+\infty&-\infty\\\hline
+\infty&+\infty&+\infty&$F.I.$\\\hline
-\infty&-\infty&$F.I.$&-\infty\\\hline
\end{tabular}
\end{document}