[Ethereal-users] display filter for pop3?

[Agryppa <agrypa1@xxxxxxxxxxxxxx>]

Hi,
I only want to see those pop3 transmissions that have some payload in it and 
see the USER field, too. So I did this in display filter:

pop contains USER and pop contains RETR

It doesn't work, though. The two statements work separately bu not togather.
How to make it work?

thanks for any hints
-- 
Agryppa