%%
%% The LaTeX Companion, 3ed
%%
%% Example 11-6-3 on page II-194 in "Operator and function names".
%%
%% 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{171.0pt}

%StartShownPreambleCommands
\usepackage{amsmath}
\DeclareMathOperator \meas    {meas}
\DeclareMathOperator*\esssup  {ess \, sup}
\DeclareMathOperator*\supminus{sup - minus*}
\newcommand\abs [1]{\lvert#1\rvert}
\newcommand\norm[1]{\lVert#1\rVert}
%StopShownPreambleCommands

\begin{document}
\begin{multline*}
 \norm{f}_\infty = \esssup_{x \in R^n} \abs{f(x)} \\
 \meas_1 \{ u \in R_+^1 \colon f^*(u)>\alpha \} = \\
 \esssup_{x \in R^i} \; \meas_i
   \{ u \in R^n \colon \abs{f(u)} \geq \alpha \}  \\
 (\forall \alpha \in \supminus_{f^*} R_{*+})
\end{multline*}
\end{document}