Combining voices in a piano score

[Christopher R. Maden]

I am working on a four-part choral score with piano accompaniment.  A
simplified version is attached.[*]

The vocal score looks great.  Stems are in different directions for the
different voices, exactly as I want.

However, I would like the piano score, based on the exact same music
objects, to combine the voices into chords and single notes as
appropriate, and I can’t seem to figure out how to flatten the voices
together.  I’ve tried various invocations of \oneVoice, but they don’t
seem to do anything.

[Also interesting is what happens if you get rid of the \key declaration
in the piano staves; LilyPond seems to give up on creating chords
altogether and just madly overlaps notes.]

If I am just missing something in the doc, I’d love a pointer.

Thanks,
Chris

[*] It is a mangled-for-demonstration version of “The Old Oaken Bucket,”
in case you were wondering.
-- 
Chris Maden, text nerd  <URL: http://crism.maden.org/ >
“Be wary of great leaders.  Hope that there are many, many small
 leaders.” — Pete Seeger

four_part_test.ly
Description: Text Data