absolute pitches in relative mode

[Kenneth Teh]

I writing a piano arrangement with polyphony and I
find myself correcting the absolute pitches a lot.  I
can't figure out how the octave of the next note is
determined.  If it's a single note, there's no
problem, but if the precedent is a chord how does Lily
figure out the pitch of the following note.  My chord
voicings are usually open so they span a seventh or a
tenth.

Relatedly, how do I use \octave?  I tried with \octave
bf1 and it barfed saying 'unexpected DIGIT'.  But,
this is what I really wanted.  Bflat between c and c'
as a whole note.

Thanks! 

Ken