Why this R ggplot subscript is not working? : <p>Code where trying to apply <code>g + labs(y=expression(N_{s}))</code> with the following error which does not make sense</p>

<pre><code>g &lt;- ggplot(datm, aes(variable, value, fill=gender)) + geom_bar(stat="identity", position = position_dodge()) + facet_grid(male.Nij ~ group) + xlab("Association type") + ggtitle("View")
#http://stackoverflow.com/a/17335258/54964
g + labs( y=expression(N_{s}) )
</code></pre>

<p>I get</p>

<pre><code>Error: unexpected '{' in "g + labs( y=expression(N_{"
Execution halted
</code></pre>

<p>R: 3.3.2 backports<br>
OS: Debian 8.5    </p>
