Polyphony?

[Jonathan Rosanowski]

I'm using lilypond for cygwin 1.6.0.
I'm trying to write some guitar music. Sometimes the bass notes may ring on 
while notes above play. I'm guessing that I need to write this using polyphony. 
Is that correct? If so, then how do you enter a quarter note bass with two 
eight notes above it. 
I tried this < c8 e a \\ {a,4}> < c8 e a > but it pushes the second chord out 
to the next quarter note position.
Here's the whole line
r4 < f8 ees' c' > < e d' b' > r4 < c8 e a \\ {a,4}> < c8 e a > ~ 

Thanks,
Jonathan.