LaTeX maths export problems

[Nick Higham <highamnj@gmail.com>]

I use Org for producing LaTeX (e.g., all of https://github.com/higham/what-is
is produced from Org source).

I'm finding that Org has trouble parsing some LaTeX maths expressions and
I then have to make seemingly arbitrary tweaks to get it to parse correctly.

I thought this might be to do with something in my .emacs, but the same
problem happens with a bare bones Emacs. A simple example is this file:

#################################################################
# ex1a_bad.org
\[
     \widehat{y} = f(x+\widehat{x}) + \Delta y,
     \quad |\widehat{y}| \le \epsilon |y|, \;
           |\widehat{x}| \le \epsilon |x|
\]
#################################################################

With emacs -q and

  This is GNU Emacs 26.3 (build 1, x86_64-w64-mingw32) of 2019-08-29
  org-version is a variable defined in 'org.el'. Its value is "9.1.9"

I get as the exported LaTeX:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Created 2020-08-13 Thu 01:36
% Intended LaTeX compiler: pdflatex
\documentclass[11pt]{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{graphicx}
\usepackage{grffile}
\usepackage{longtable}
\usepackage{wrapfig}
\usepackage{rotating}
\usepackage[normalem]{ulem}
\usepackage{amsmath}
\usepackage{textcomp}
\usepackage{amssymb}
\usepackage{capt-of}
\usepackage{hyperref}
\date{\today}
\title{}
\hypersetup{
 pdfauthor={},
 pdftitle={},
 pdfkeywords={},
 pdfsubject={},
 pdfcreator={Emacs 26.3 (Org mode 9.1.9)},
 pdflang={English}}
\begin{document}

\tableofcontents

$\backslash$[
     \widehat{y} = f(x+\widehat{x}) + \(\Delta\) y,
     \quad |\widehat{y}| \(\le\) \(\epsilon\) |y|, $\backslash$;
\begin{center}
\begin{tabular}{lll}
\widehat{x} & \(\le\) \(\epsilon\) & x\\
\end{tabular}
\end{center}
$\backslash$]
\end{document}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

The backslashes are being interpreted literally and the pipes are being
interpreted as a table.  Yet this version processes correctly:

#################################################################
# ex1a_good.org
\[
    \widehat{y} = f(x+\widehat{x}) + \Delta y,
    \quad |\widehat{y}| \le \epsilon |y|, \; |\widehat{x}| \le \epsilon |x|
\]
#################################################################

I have other simple examples like this one.

The same thing happens with my usual Emacs configuration, which uses Org 9.3.7.

---Nick Higham