[R] greek in main title

[Oldradio69@aol.com]

Hello,

I have written a function that demonstrates the CLT by
generating samples following the exponential distribution,
calculating the means, plotting the histogram, and drawing
the limiting normal curve as an overlay.  I have the title
of each histogram state the sample size and rate (1/theta)
for the exponential (the output is actually 4 histograms),
but I can't get the greek letter theta to appear in the
heading.  Is this possible?  I can get nontext for the xlab 
and ylab pretty easily.

Thanks, Jason

Below is my code.  Currently it just writes out "theta."

function (theta) 
{
  layout(matrix(c(1:4),2,2,byrow=TRUE))
  par(bg = "cornsilk")
  n <- c(1,10,25,50)
  for(i in 1:4)  {
     xbar <- rep(0, 1000)
     for (j in 1:1000)
        xbar[j] <- mean(rexp(n[i], rate = 1/theta))
     heading <- paste("Exp w/ theta =", theta, ", n = ", n[i])
     hist(xbar, prob = TRUE, breaks = "FD", main = title(heading, font.main = 6), 
          col = "lightgray", xlab = expression(bar(x)))
     xbar <- sort(xbar)
     points(xbar, dnorm(xbar, mean = theta, sd = theta/sqrt(n[i])), 
        type = "l", col = 2)
    }
}