[R] prime in expression in plot

[Thomas Steiner]

> how do I add the "prime" (first derivative) to a R-plot?

sorry for the noise, I found it myself:
http://finzi.psych.upenn.edu/R/Rhelp02a/archive/20984.html
I use now (works fine)
plot(1,1,xlab=expression(frac("F'"(0),"R'"(0))),xaxt="n")
Thomas