%%
%% The LaTeX Companion, 2ed (second printing August 2004)
%%
%% Example 8-4-7 on page 493.
%%
%% 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{183.0pt}

\StartShownPreambleCommands
\usepackage{amsmath}
\StopShownPreambleCommands
\begin{document}
\begin{align*}
  u & \equiv v + 1 \mod{n^2}  \\
  u & \equiv v + 1 \bmod{n^2} \\
  u &   =    v + 1 \pmod{n^2} \\
  u &   =    v + 1 \pod{n^2}
\end{align*}
The in-text layout: $ u = v + 1 \pmod{n^2} $
\begin{gather*}
   (m \bmod n) = k^2 \, ; \quad
  x \equiv y \pmod b \, ;     \\
  x \equiv y \mod c \, ;  \quad
  x \equiv y \pod d\, .
\end{gather*}
\end{document}