%%
%% 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}
&\approx \overleftarrow {\psi_\Delta(t) E_t h}
& &   \text{No style change}             \\[-3pt]
& & & \text{without \textsf{amsmath}}    \\
\underrightarrow  {\psi_\delta(t) E_t h}
&\simeq \underleftarrow  {\psi_\Delta(t) E_t h}
& & \text{Needs \textsf{amsmath}}         \\
\overleftrightarrow {\psi_\delta(t) E_t h}
&\sim \underleftrightarrow{\psi_\Delta(t) E_t h}
& & \text{Needs \textsf{amsmath}}
\end{align*}
\end{document}
