title: How to include subscript in text for plot point labels
body: <p>Hi I'm new to R so I apologise if this is a very basic question.
  I'm trying to add text to a plot at point 11 on the x axis and point 900 on the y axis that will read <code>t0= -4.0280</code> with the 0 as subscript. Where <code>t0 &lt;- -4.0280</code>
   To do this I've tried:</p>
  
  <pre><code>text(11,900,paste("t[0]=",t0),cex=0.8) 
  # which gives 
  't[0]= -4.0280'
  
  text(11,900,expression(paste("t[0]=",t0)),cex=0.8) 
  # which gives 
  't[0]=t0'
  
  # the closest I've gotten is:    
  text(11,900,expression(paste(t[0]==t0)),cex=0.8)
  </code></pre>
  
  <p>which will use subscript but return <code>t0</code> instead of my value of -4.0280.</p>
  
  <p>Could anyone show me where Ive gone wrong?</p>
  
  <p>Cheers.</p>