Staff Changes

[Yuval Harel]

Hello,

	I've been trying to move a voice across staffs. I looked at the  
documentation at:
http://lilypond.org/doc/v2.2/Documentation/user/out-www/lilypond/Manual-staff-switches.html#Manual%20staff%20switches
but couldn't get that to work.
Even before getting to the staff change itself, I couldn't get the staffs  
defined before they are used, unless
they're in the same \score block.

What I did manage to get to work is this:

\score {
        \notes \transpose c c' {
                \context PianoStaff = PS <<
                        \context Staff = RH {}
                        \context Staff = LH {}
                        \context Staff = RH {
                                g \change Staff=LH f
                        }
                >>
        }
}


But then I can't put the music inside variables before the score, because  
it uses \change.
How do I make this work? Is there any example of this?

Thanks,
        Yuval