title: How to superscript a - (minus symbol) in a legend title with qpolot in ggplot2 in R
body: <p>I'm trying to superscript a '-' straight after a subscript 4 in an axis title in ggplot2 using bquote.  I'm so close!  The following gives me everything EXCEPT a small, superscript - straight after the subscript 4:</p>
  
  <pre><code>qplot(uptake, data = CO2) +  
  ylab(bquote('Membrane available NH '[4]*'-N (  '*mu*'g' ~ resin^-1* ~ 14~day^-1*')'))
  </code></pre>
  
  <p>I've tried playing around the ^, for example:</p>
  
  <pre><code>qplot(uptake, data = CO2) +  
  ylab(bquote('Membrane available NH '[4]*^-'-N (  '*mu*'g' ~ resin^-1* ~ 14~day^-1*')'))
  </code></pre>
  
  <p>But get error messages such as:</p>
  
  <pre><code>Error: unexpected '^' in "qplot(uptake, data = CO2) +  
  ylab(bquote('Membrane available NH '[4]*^"
  </code></pre>
  
  <p>Clearly I'm not expressing the ^ correctly.</p>
  
  <p>Any help would be greatly appreciated.</p>
  
  <p>Many thanks!</p>