[R] Simple qqplot question

[Ralf B]

I am a beginner in R, so please don't step on me if this is too
simple. I have two data sets datax and datay for which I created a
qqplot

qqplot(datax,datay)

but now I want a line that indicates the perfect match so that I can
see how much the plot diverts from the ideal. This ideal however is
not normal, so I think qqnorm and qqline cannot be applied.

Perhaps you can help?

Ralf