riff notation

[Jan Kohnert]

I'd like to write a piece and there I have a "guitar riff" f.e.:

< a4 e' a' c'' e'' a'' > \times 2/3 { < a16 e' a' c'' e'' a'' > ~ < a e' a' 
c'' e'' a'' > r r r r r r < gis gis' c'' e'' gis'' > r r r < gis gis' c'' e'' 
gis'' > ~ < gis gis' c'' e'' gis'' > < gis gis' c'' e'' gis'' > r r r } 
and so on...

This riff is repeated very often and so the lily-file is very hard to read.
So this is my question:
Is it possible to define the riff one time, maybe:
define riff = { a b c }
and then just use it in the notes:
\score \notes {
  riff riff riff
}
It would make the file much more easy to read, but I don't know if and how to 
use.

Thank you for your help.

Regards Jan Kohnert