%%
%% The LaTeX Companion, 3ed
%%
%% Example 11-8-5 on page II-214 in "Letters, numerals, and other Ordinary symbols".
%%
%% 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{135.0pt}

  % Shorten the vertical size of the example ...
  \AtBeginDocument{%
    \setlength\abovedisplayskip{.5\abovedisplayskip}%
    \setlength\belowdisplayskip{.5\belowdisplayskip}%
  }

%StartShownPreambleCommands
\usepackage[fleqn]{amsmath}   \usepackage{amssymb}
\DeclareMathSymbol\bneg   {\mathbin}{symbols}{"3A}
\DeclareMathSymbol\rsquare{\mathrel}{AMSa}{"03}
\thickmuskip=10mu plus 5mu
%StopShownPreambleCommands

\begin{document}
\noindent Symbols of wrong class (ord):
\[ a \neg b           \qquad  x \square           y + z \]
Manual correction:
\[ a \mathbin{\neg} b \qquad  x \mathrel{\square} y + z \]
Symbols of correct class:
\[ a \bneg          b \qquad  x \rsquare          y + z \]
\end{document}