[R] adding text to the top corner of a lattice plot

[Rajarshi Guha]

Hi, I have a series of lattice plots which I am arranging in a 2x2
grid via print:

print(p.preds, split=c(1,1, 2,2), more=TRUE)
print(p.comp, split=c(2,1,2,2), more=TRUE)
print(p.bw, split=c(1,2,2,2), more=FALSE)

What I'd like to have is a letter (A, B, ...) in the top corner of
each plot. While panel.text lets me add text anywhere within a plot, I
can't seem to workout how I could put some text in the top left
corner, say, of the whole plotting region.

Any pointers would be appreciated

-- 
Rajarshi Guha
NIH Chemical Genomics Center