Problem with factorials in nomenclature environment

Question

I am using the following code

\documentclass{article}
\usepackage{nomencl}
\makenomenclature
\renewcommand{\nomname}{List of Abbreviations}
\begin{document}
\addcontentsline{toc}{section}{List of Abbreviations}
\nomenclature{(\mathbb N_r)}{Set of all positive integers greater than or equal to $r!$}
\printnomenclature
\end{document}

But for some reason I cannot make the factorial above work. The "!" is pushing the sentence to the next line. Any suggestion to remedy this issue is appreciated. Thank you!

Answer 1

Heyo!

First of all your MWE doesn't compile, because \mathbb requires the amssymb package.

Now to your actual question, the problem is: nomencl package doesn't allow exclamation marks in keys

Workaround #1:

As suggested in the linked question, you can fix this by escaping the exclamation mark:

\nomenclature{\(\mathbb{N}\)}{Set of all positive integers greater than or equal to \(r%!\)}

However, this breaks the syntax highlighting in Overleaf and throws errors there (even though it compiles just fine).

Workaround #2

Add the following to the preamble:

\newcommand{\bang}{\mathrm{!}}

and then

\nomenclature{\(\mathbb{N}\)}{Set of all positive integers greater than or equal to \(r\bang\)}

This does not break the syntax highlighting in Overleaf. See What's the difference between \mathrm and \operatorname? for an explanation of \mathrm.

Answer 2

The package nomencl relies on makeindex for sorting and massaging the nomenclature entries.

For makeindex the character ! is special so it should be quoted in material passed to it. What's “quoting” in makeindex?

The makeindex style file, in this case nomencl.ist, may contain a line such as

quote "%"

If no quote line is present in the style file, the default for makeindex is " and you could type in your entry as

\nomenclature{\(\mathbb{N}_{r}\)}{Set of all positive integers greater than or equal to $r"!$}

This happened to annoy German users, because babel makes " into a shorthand character, so starting from nomencl version 2.5 the nomencl.ist file contains

quote '%'

(double or single quotes can be used there for isolating the string). Thus you can input your entry as

\nomenclature{\(\mathbb{N}_{r}\)}{Set of all positive integers greater than or equal to $r%!$}

but, of course, this breaks the syntax coloring/checking of editors (in particular the one in Overleaf that tries to check syntax on the fly). The LaTeX run would be good even if the point is marked “wrong”.

What we could do is to replace the special characters in the arguments before passing them to \nomenclature. You can judge if this is worth the pain. In the code [\!\@] stands for the list of special characters we want to quote with a %.

% arara: pdflatex
% arara: nomencl
% arara: pdflatex
\documentclass{article}
\usepackage[intoc]{nomencl}
\usepackage{amssymb}
\makenomenclature
\renewcommand{\nomname}{List of Abbreviations}
\ExplSyntaxOn
\NewCommandCopy{\originalnomenclature}{\nomenclature}
\RenewDocumentCommand{\nomenclature}{O{}mm}
 {
  \shaya_nomencl:nnn { #1 } { #2 } { #3 }
 }
\tl_new:N \l_shaya_nomencl_one_tl
\tl_new:N \l_shaya_nomencl_two_tl
\cs_new_protected:Nn \shaya_nomencl:nnn
 {
  \tl_set:Nn \l_shaya_nomencl_one_tl { #2 }
  \tl_set:Nn \l_shaya_nomencl_two_tl { #3 }
  \regex_replace_all:nnN { [!@] } { \cO%\0 } \l_shaya_nomencl_one_tl
  \regex_replace_all:nnN { [!@] } { \cO%\0 } \l_shaya_nomencl_two_tl
  __shaya_nomencl:nVV { #1 } \l_shaya_nomencl_one_tl \l_shaya_nomencl_two_tl
 }
\cs_new_protected:Nn __shaya_nomencl:nnn
 {
  \originalnomenclature[#1]{#2}{#3}
 }
\cs_generate_variant:Nn __shaya_nomencl:nnn { nVV }
\ExplSyntaxOff
\begin{document}
\tableofcontents
\section{Introduction}
Some text
\nomenclature{(\mathbb{N}_{r})}{Set of all positive integers greater than or equal to $r!$}
\printnomenclature
\end{document}

Please, note that \mathbb N is not the best way to input the symbol and it should be \mathbb{N}. Also, if you want to insert the nomenclature in the table of contents, use the intoc option, rather than doing it manually.