[R] lattice/xyplot: plotting 4 variables in two panels - can this be done?

[Søren Højsgaard]

Hi,
I would like to create a plot of y1,y2,y3,y4 against x for several subjects such that y1 and y2 are plotted against x in one panel and y3 and y4 against x in another panel. Thus if there are 3 subjects I should end up with 6 panels. Is there a simple way of doing so (i.e. without calling xyplot() several times, and then padding the results together)?? 
Regards
Søren