title: use lapply and plot to draw multiple plots
body: <p>try to run the following code, but always got error message:</p>
  
  <blockquote>
    <p>Error in text.default(x, y, txt, cex = cex, font = font) : invalid
    mathematical annotation</p>
  </blockquote>
  
  <pre><code>par(mfrow=c(2,3))
  x &lt;- c(1:4,6:9)
  myPlot&lt;-function(x){
      plot(pros.dat, pros.dat$svi ~ pros.dat[,x])
  }
  lapply(c(1:4,6:9), FUN=myPlot)
  </code></pre>
  
  <p>Could anybody tell me what's wrong? Thanks</p>