%%
%% The LaTeX Companion, 2ed (second printing August 2004)
%%
%% Example 8-8-5 on page 511.
%%
%% Copyright (C) 2004 Frank Mittelbach, Michel Goossens,
%%    Johannes Braams, David Carlisle, and Chris Rowley
%%
%% 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{ttctexa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{348.0pt}

\StartShownPreambleCommands
\usepackage{amsmath,amssymb,txfonts,bm}
\newcommand\bfB{\mathbf{B}}
\newcommand\bfx{\mathbf{x}}
\bmdefine\bpi{\pi}  \bmdefine\binfty{\infty}
\StopShownPreambleCommands
\begin{document}
\section{The bold equivalence
  $\sum_{j < B} \prod_\lambda : \bm{\sum_{x_j} \prod_\lambda}$}
\begin{gather}
  B_\infty + \pi B_1 \sim  \bfB_{\binfty} \bm{+}\bpi \bfB_{\bm{1}}
    \bm {\sim B_\infty + \pi B_1}                               \\
  B_\binfty + \bpi B_{\bm{1}} \bm{\in} \bm{\biggl\lbrace}
    (\bfB, \bfx) : \frac {\partial \bfB}{\partial \bfx}
    \bm{\lnapprox} \bm{1} \bm{\biggr\rbrace}
\end{gather}
\end{document}