[R] prime in expression in plot

[Thomas Steiner]

I want to write something like (LaTeX style)
b_{norm}=\frac{F\prime(0)}{R\prime(0)}

how do I add the "prime" (first derivative) to a R-plot? The help of
"plotmath" just talks about "partialdiff". Can you complete this
command?

text( 30,0.05,labels=expression(b[plain("norm")]==frac(F(0),R(0))) )

Thanks,
Thomas