%%
%% The LaTeX Companion, 3ed
%%
%% Example 11-2-36 on page II-151 in "Fine-tuning tag placement".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See https://www.latex-project.org/lppl.txt for details.
%%

\documentclass{tlc3examargin}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{278.40106pt}

  % Shorten the vertical size of the example ...
  \AtBeginDocument{%
    \setlength\abovedisplayskip{.2\abovedisplayskip}%
    \setlength\belowdisplayskip{.7\belowdisplayskip}%
  }

%StartShownPreambleCommands
\usepackage{amsmath}
%StopShownPreambleCommands

\begin{document}
\begin{equation}  \begin{split}
  \lvert I_2 \rvert  &=    \left\lvert \int_{0}^T \psi(t)
      \left\{  u(a, t) - \int_{\gamma(t)}^a \frac{d\theta}{k}
        (\theta, t) \int_{a}^\theta c (\xi) u_t (\xi, t) \,d\xi
      \right\} dt \right\rvert                                     \\
                     &\le  C_6  \Biggl\lvert
      \left\lvert f \int_\Omega \left\lvert
          \widetilde{S}^{-1,0}_{a,-} W_2(\Omega, \Gamma_l)
        \right\rvert \ \right\rvert
      \left\lvert \lvert u \rvert
        \overset{\circ}{\to} W_2^{\widetilde{A}} (\Omega; \Gamma_r,T)
      \right\rvert              \Biggr\rvert
\end{split} \end{equation}
A line of text after the equation \ldots
\end{document}
