%%
%% The LaTeX Companion, 3ed
%%
%% Example 11-8-9 on page II-218 in "Relation 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{tlc3exa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{87.0pt}

%StartShownPreambleCommands
\usepackage{centernot}
%StopShownPreambleCommands

\begin{document}
$ \not\parallel       \ \not\frown       \ \not\longmapsto $  \par
$ \centernot\parallel \ \centernot\frown \ \centernot\longmapsto   $
\end{document}