Dear Peter,
I fear, this one was easy to miss, given the screenshot you sent us. ;)
It looks like you can put the part we had till now into a lowerVoice variable, with the newly introduced upper voice into another and then partCombine does a pretty good job. I don't know if this is a dirty hack to feed partCombine already polyphonic music, but the result looks decent to me - at least for now.
The doubled stem at the last note might hint that it is a note used in both voices - therefore I would assume it splits again on the next beat?
upperPart = \relative {
\voiceOne
s1. |
s4. s8
\partCombineApart
c( e b4. ~ 4 b,8) |
}
lowerPart = {
{ <<
\relative {
b,4.~( 8 c e <b~ e,>4. 4 b,8 |
\stemDown <e) e,>2. ~ \stemDown <e e,>4. c4\rest b8 |
}
\\
\relative
{
e,2.~ \hide Stem 4.~ 4 \revert Voice.Stem.transparent s8 |
f'4.\rest f8\rest
}
>>
}
}
\score {
\new Staff {
\time 12/8
\clef "bass"
<<
\partCombine \upperPart \lowerPart
>>
}
}
All the best
Christian