%%
%% The LaTeX Companion, 3ed
%%
%% Example 11-5-6 on page II-183 in "Horizontal extensions in standard \LaTeX {}".
%%
%% 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
%StopShownPreambleCommands
\begin{document}
\[ \widehat {\psi_\delta(t) E_t h} \neq
\widetilde {\psi_\Delta(t) E_t h}
\]
\[ \overline {\psi_\delta(t) E_t h} \approx
\underline {\psi_\Delta(t) E_t h}
\]
\[ \overrightarrow {\psi_\delta(t) E_t h} \cong
\overleftarrow {\psi_\Delta(t) E_t h}
\]
Combinations are possible too:
\[ \overline {\overline {\psi_\delta(t) E_t h}}
\leq
\underline {\overrightarrow
{\psi_\Delta(t) E_t h}}
\]
Braces have extra possibilities as explained below.
\[ \overbrace {\psi_\delta(t) E_t h} \doteq
\underbrace {\psi_\Delta(t) E_t h}
\]
\end{document}
