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In section 3.15 of the Short Math Guide for LaTeX, it says

When predefining such a named operator is problematic (e.g., when using one in the title or abstract of an article), there is an alternative form that can be used directly,

Why is using a named operator in the title or abstract problematic?

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1 Answer 1

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Note that the guide originates as a guide for writing for American Math Society publications. The abstract and title of such submissions are routinely extracted eg to use in Math Reviews or other catalogues of metadata. Having any document-defined commands can be problematic for such use as you need to somehow carry them along with the fragments used for the abstract so that the abstract can be used in the document and also separately in an abstracts publication or have the title or abstract converted to HTML.

There is however an issue with using these commands in section titles, but it it is not resolved by using \operatorname. Hyperref can not (currently) automatically generate pure text versions to use in PDF bookmarks so you get warnings and nonsense in the bookmark pane unless you supply the text version using \texorpdfstring

\documentclass{article}
\usepackage{amsmath}
\usepackage{hyperref}
\DeclareMathOperator\zzz{abc}

\begin{document}

\tableofcontents
\section{$\zzz\pi$}
aaa

\section{$\zzz\phi$}
aaa

\end{document}

Produces the warnings

Package hyperref Warning: Token not allowed in a PDF string (Unicode):
(hyperref)                removing `\symoperators' on input line 12.

enter image description here

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  • Thank you for not only answering my original question, but providing an insight regarding the issue around the hyperref functionality.
    – Jay Lee
    Dec 6, 2021 at 11:14

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