<html><head><meta name="color-scheme" content="light dark"></head><body><pre style="word-wrap: break-word; white-space: pre-wrap;">%%
%% The LaTeX Companion, 3ed
%%
%% Example 11-5-8 on page II-184 in "Further horizontal extensions".
%%
%% 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{183.0pt}

  \usepackage{lmodern}

%StartShownPreambleCommands
\usepackage{amsmath}
%StopShownPreambleCommands

\begin{document}
\begin{align*}
\overrightarrow {\psi_\delta(t) E_t h}
&amp;\approx \overleftarrow {\psi_\Delta(t) E_t h}
&amp; &amp;   \text{No style change}             \\[-3pt]
&amp; &amp; &amp; \text{without \textsf{amsmath}}    \\
\underrightarrow  {\psi_\delta(t) E_t h}
&amp;\simeq \underleftarrow  {\psi_\Delta(t) E_t h}
&amp; &amp; \text{Needs \textsf{amsmath}}         \\
\overleftrightarrow {\psi_\delta(t) E_t h}
&amp;\sim \underleftrightarrow{\psi_\Delta(t) E_t h}
&amp; &amp; \text{Needs \textsf{amsmath}}
\end{align*}
\end{document}
</pre></body></html>