# What is the error runaway argument in the following code?

Here is my code

\documentclass{article}
\usepackage{multicol}
\title{IELTS Course Companion}
\author{Ethen Hu}

\begin{document}
\setlength{\parindent}{0pt}
\maketitle
\section{numbers}
\subsection{question\footnote{OG 3.1}}
\begin{multicols}{2}
\renewcommand{\labelenumi}{\alph{enumi}}
\begin{enumerate}
\item 1st/3rd
\item \$10.50/\$10.15
\item 6th/5th
\item 17/70
\item 19/90
\columnbreak
\item 15/50
\item 52/62
\item \pounds110/\pounds810
\item 31st/33rd
\item 22nd/27th
\end{enumerate}
\end{multicols}

%\subsection{question 2 \footnote{OG 3.3}

\end{document}


This is successfully compiled on overleaf, but with a warning:argument of@sect has an extra}. runaway argument?

This is the error page incase it is of anyhelp. I guess it has something to do with trying to put a footnote on

Adding the optional argument to subsection, like this,

\subsection[question]{question\footnote{OG 3.1}}


lets you add the \footnote without fuss, and your example runs nicely.

• Thanks for your reply. Would you please expand on what was wrong with my code what does the [question] argument do. Thanks so much. – jxhyc Apr 28 '20 at 12:42
• I don't really know about what is happening behind the scenes, but you will find a range of more or less deep explanations in the usual literature, e.g. Nasa pages. If you can get hold of a copy of the The LaTeX Companion (2nd edn.), it's great for this kind of explanation, but you should be able to find a lot online. – Juan del Acebo Apr 28 '20 at 22:10
 \title{IELTS Course Companion}
\author{Ethen Hu}

\begin{document}

\maketitle

\section{numbers}
\subsection{question}
{\footnote{OG 3.1}}

\begin{tabular}{cc}
$1^{st}$ & $3^{rd}$\\
\$10.50 &\$ 10.15\\
$6^{th}$ & $5^{th}$\\
17 & 70\\
19& 90\\
&\\
15 & 50\\
52 & 62\\
Lb 110 &  Lb 810\\
$31^{st}$ & $33^{rd}$\\
$22^{nd}$ & $27^{th}$\\
\end{tabular}

\end{document}


I thought this is what you. Multicolumn are meant for tabular environment and item for enumuration. Please check whether this is what you wanted.