Polyphonic alternating beams with cross-voice slurs

[Matthias Kilian]

Hi,

finally beeing back to LilyPond after nearly a year, I'm restarting
at a really weird engraving problem. Erik Sandberg warned be, and
he was right. This is what I want:

http://dead-parrot.de/chaconne.gif

or, if you prefer PDF:

http://dead-parrot.de/chaconne.pdf

The alternating beams aren't the problem, I just use the tip in

http://lilypond.org/doc/v2.4/input/test/out-www/collated-files.html

However, I don't know how to get the (technically) cross-voice slurs
managed.

Any idea is welcome.

Ciao,
        Kili