Re:why chords with notes of different duration is not, supported?

[Mats Bengtsson]

I resend my patch that will do the right thing when just writing
> > <<  g,4 d'4 b'4 g'2>>

A couple of comments:

If I were to typeset this chord, my first choice would be to tweak the 
duration-log of some of the note-heads within a normal chord, see for 
example 
http://lists.gnu.org/archive/html/lilypond-user/2010-10/msg00188.html. 
Agreed, this is an ugly syntax that requires a good understanding of the 
LilyPond internals, even though the technique explicitly is mentioned in 
the section on Tweak, in the Notation Reference. This could be an answer 
to Grahams question on how to implement the feature internally in LilyPond.

We shouldn't blame Bach! If you look at his autograph, you will see that 
he uses separate stems for the different notes. This has been very 
thoroughly imitated in the edition prepared by late Werner Icking, see 
for example the first bars of 
http://icking-music-archive.org/scores/bach/sonatas_and_partitas/bwv1001.pdf 
(typeset using MusiXTeX), in case you don't have access to a good copy 
of the autograph and think that 
http://upload.wikimedia.org/wikipedia/commons/a/a5/BWV1001.jpg is too 
small. However, there are many other composers that use the notation you 
are discussing (in addition to lots of editions of Bach).

    /Mats