setting systems per page in lilypond-book

[Adam Good]

Hi,
How do I specify how many systems per page when I'm using Lilypond- 
book? I've read the manual (Integrating LaTeX and music) and have  
tried examples but I can't get it working, I'm not sure what I'm  
doing wrong.

in the very simple example below there are 6 systems total. what sort  
of \def\betweenLilyPondSystem can I use to say that there must be 3  
systems, then a page break?

thank you SOO much!

Adam

%%%%%%%%%%%%%%%%%%
\documentclass[a4paper]{book}

\begin{document}

\begin[fragment]{lilypond}
\relative c' {c1 d e f \break g a b c, \break d e f g \break a b c, d  
\break e f g a \break b c d}
\end{lilypond}

\end{document}