%%
%% Der LaTeX-Begleiter, zweite Auflage (September 2005)
%%
%% Beispiel 8-8-2 von Seite 523.
%%
%% Copyright (C) 2005 Frank Mittelbach, Michel Goossens,
%%    Johannes Braams, David Carlisle, and Chris Rowley
%%
%% Uebersetzung: Copyright (C) 2005 Claudia Krysztofiak,
%%    Rebecca Stiels und Frank Mittelbach
%%
%% 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{lb2exa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{89.4372pt}

\StartShownPreambleCommands
\usepackage{amsfonts}
\DeclareMathAlphabet\mathbb{U}{fplmbb}{m}{n}
\StopShownPreambleCommands
\begin{document}
$ \lbrace n,m \in \mathbb{N} \mid  \mathfrak{N}_{n,m} \rbrace $
\end{document}