In latex, the integral symbol '\int' displays as '\Delta' in the compiled pdf, why? - latex

Question

This happens in some (but not all) documents, where '$\int$' in an equation displays as '$\Delta$' in the compiled pdf. For those documents, I tried both Winedt and Overleaf and the same things just happen.
The problem can be replicated by using the following codes in the main.tex file:
\documentclass[a4paper,10pt]{autart}
\pagestyle{plain}
\date{\today}
\usepackage{esint}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\setlength {\marginparwidth }{2cm}
\begin{document}
\begin{frontmatter}
\title{Generalized $t$-Distribution Noise Model\thanksref{footnoteinfo}}
\thanks[footnoteinfo]{Acknowledgement...}
\author[AuthorCategory1]{Author 1}\ead{author1#somewhere}
\author[AuthorCategory2]{Author 2}\ead{author2#somewhere}
\address[AuthorCategory1]{Address 1}
\address[AuthorCategory2]{Address 2}
\begin{abstract}
---
\end{abstract}
\end{frontmatter}
\section{This is a section}
\begin{eqnarray}
\int \nonumber
\end{eqnarray}
\end{document}
The autart.cls can be found online, for example at https://hal.archives-ouvertes.fr/file/index/docid/514508/filename/autart.cls
You will get a result like this:
And from my own exploration, the problem can be solved surprisingly if changing the title from
\title{Generalized $t$-Distribution Noise Model\thanksref{footnoteinfo}}
to
\title{Title\thanksref{footnoteinfo}}
And you will get the correct integral symbol as follows:
It seems that you can also solve the problem by removing the "esint" package, or change the document class from autart to article. I guess there is some conflicts defined in these class/packages, maybe, and result in this funny phenomenon.
Is there a way to solve the problem without changing the title, while using autart document class and esint package?
Thanks.

Answer 1

Ironically, the problem is in the \no#harm macro your class defines, which redefines \protect. You can work around the problem by removing this defintion like this:
\documentclass{autart}
\pagestyle{plain}
\date{\today}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{xpatch}
\makeatletter
\xpatchcmd{\no#harm}{\def\protect{\noexpand\protect\noexpand}}{}{\typeout{patch ok}}{\typeout{patch fail}}
\makeatother
\usepackage{esint}
\setlength {\marginparwidth }{2cm}
\begin{document}
\begin{frontmatter}
\title{Generalized $t$-Distribution Noise Model\thanksref{footnoteinfo}}
\thanks[footnoteinfo]{Acknowledgement...}
\author[AuthorCategory1]{Author 1}\ead{author1#somewhere}
\author[AuthorCategory2]{Author 2}\ead{author2#somewhere}
\address[AuthorCategory1]{Address 1}
\address[AuthorCategory2]{Address 2}
\begin{abstract}
---
\end{abstract}
\end{frontmatter}
\section{This is a section}
\begin{eqnarray}
\int \nonumber
\end{eqnarray}
\end{document}