Math equation in latex (varnothing)

Question

In a pseudocode, I would like to assign \varnothing to a variable.
My code goes like this:

\documentclass[runningheads]{llncs} 
\usepackage{graphicx} 
\usepackage{algpseudocode} 
\usepackage{algorithm}
\usepackage{amsmath}
\begin{document}
\begin{algorithm} 
\caption{Find...} 
\begin{algorithmic}[1] \State $RS$ $\leftarrow$ $\varnothing$ \end{algorithmic} 
\end{algorithm} 
\end{document}

Unfortunately this doesn't work. The error message I got is the following:

State $RS$ $\leftarrow \varnothing $ The control sequence at the end
of the top line of your error message was never \def'ed. If you have
misspelled it (e.g., `\hobx'), type `I' and the correct spelling
(e.g., `I\hbox'). Otherwise just continue, and I'll forget about
whatever was undefined. ! Undefined control sequence. 
\varnothing l.103 ...\quad \quad $R$ $\leftarrow$ $\varnothing $
\Comment{$R$ is the set ... The control sequence at the end of the top
line of your error message was never \def'ed. If you have misspelled
it (e.g., `\hobx'), type `I' and the correct spelling (e.g.,
`I\hbox'). Otherwise just continue, and I'll forget about whatever was
undefined.

Do you have any ides on how this can be resolved?

FYI, I've already installed amsmath from texlive-latex-base in debian 9.

Thanks,
Pavlos

Answer 1

\varnothing belongs to the set of symbols in the package amssymb. So include it in your preamble as \usepackage{amssymb} and you are good to go.

\documentclass{article} 
\usepackage{graphicx} 
\usepackage{algpseudocode} 
\usepackage{algorithm}
\usepackage{amsmath}
\usepackage{amssymb}
\begin{document}
    \begin{algorithm} 
        \caption{Find...} 
        \begin{algorithmic}[1] \State $RS$ $\leftarrow$ $\varnothing$ \end{algorithmic} 
    \end{algorithm} 
\end{document}

with which you will get: