[R] How to make legend with line+ character

[Mario Valle]

Dear all,
I have a multiline plot with each line labeled with a different letter.
But I'm not able to make the legend display the same kind of pattern 
'-a-', instead the letter is overwritten by the line. A simpler legend 
with only the letter is not very visible and the pt.bg does nothing with 
letters. Any idea?

plot(1:10,10:1,lty=1,type='b', lwd=2,pch='a')
legend("left", legend=c("ds1","ds2"), bty='n', col=1:2, 
lty=2,lwd=4,pch=letters)

Thanks for your help!
				mario
-- 
Ing. Mario Valle
Data Analysis and Visualization Group            | 
http://www.cscs.ch/~mvalle
Swiss National Supercomputing Centre (CSCS)      | Tel:  +41 (91) 610.82.60
v. Cantonale Galleria 2, 6928 Manno, Switzerland | Fax:  +41 (91) 610.82.82