Ties over 2 voices

[Phil Holmes]

I have a piece of music as shown in the attached image.  I've set this in 
LilyPond using 2 voices, the first having the 2 quavers before the bar, then 
a tie to the quaver after the bar, together with the barred semi-quavers. 
This set of 3 notes is forced stem down with \stemDown.  In the second voice 
I've put the lower crochet, and duplicated the quaver/semi-quaver barred 
notes, stem down.  It looks OK, but not surprisingly results in errors for 
clashing note columns.  I know I can turn the error off, but was wondering 
if there's a better way of doing this that doesn't rely on simply writing 
one set of notes on top of another identical set.

LilyPond snippets:

Top voice:

\voiceOne  f''8 [  c''8 ~  ]   |
\stemDown < a' c''>8 [ < a' c''>16< a' c''>16 ]  \stemNeutral  \oneVoice

Lower voice:

\voiceTwo  a'4 ~   |
< a' c''>8 [ < a' c''>16< a' c''>16 ]  \oneVoice

Thanks in advance.

--
Phil Holmes

Ties.png
Description: PNG image