Re: general questions

[Hans Forbrich]

(Following is a lengthy discussion on multiple voices - aimed at the newbie 
(such as myself) and based on my recent experience.  Apologies to the group's
experienced people for the length.)

Amelie has already answered the questions and her answer to #2 is right if the 
question is truly about chords, the following might help if it is about multiple
voices.  (Since you are new and talking about hymns, I think you want multiple 
voices)

The basic difference I like to use is:

- A chord is a 'multi pitched note' played on one instrument and shows up as 
multiple notes stacked vertically with a single ornament or articulation.  Thus
Amelie's statement about a single slur holds true.

- Multiple voices are usually different instruments (Soprano vs. Alto, 1st and 
2nd Trumpet, and so on) that may be shown on the same staff for convenience.  
Each
voice has it's own unique ornament or articulation, but if on the same staff 
the duplicated ornaments may hidden.  (Notice that an instrument capable of 
chords
usually is also capable of multiple voices.  A piano is a good example, so you 
can get both chords and multiple voices.)

So, there are a lot of possibilities for multiple voices.  Refer to the 
templates which are accessible on the web from the Lilypond home page (at
http://www.lilypond.org)

To look at your question on the slurs, consider the following (totally 
contrived) example:

Soprano:  a4 c ( ) b b ~ b a
Alto: a4 c ( ) a g e ~ e a

Using the 'chord' technique, which will cause the slur problem you notice, this 
could be written as

1.6: a4 c ( ) <b a > <b g > <b ~ e > a
1.7: a4 c ( ) <<b a >> <<b g >> ~ <<b e >> a

One alternate is to write the parts separately and combine them on a single 
staff as follows:

Soprano = \notes { a4 c ( ) b b ~ b a }
Alto = \notes {  a4 c ( ) a g e ~ e a }
\context Staff = SAvoice { < \Soprano \Alto > }

To force the Soprano stems up, Alto stems down (and appropriate slur, tie, etc. 
positioning) you could use

\context Staff = SAvoice { < \voiceOne \Soprano \voiceTwo \Alto > }

A second alternative is to use a 'main' and a 'harmony' voice allowing chords 
in the 'main' except when it causes problems:

Main = \notes { a4 c () b <<b g >> <<b e >> ~ <<b e >> a }
Harmony = \notes { s4 c () a s s s s }
\context Staff = SAvoice { < \Main \voiceTwo \Harmony > }

Notice that the \Main does not force to voice one or voice two, but the 
\Harmony does.  I find this a generally pleasing effect but you may need to 
turn off
specific harmony notes using {\property Voice.NoteHead \set #'transparent = ##t 
 ...note(s) here... \property Voice.NoteHead \revert #'transparent}.

A third alternative is to use 'parallel threads' inline as follows (see the 
mailing list discussion this week titled "stems in multiple voices per staff"):

SA = \notes { a4 < { c () a } \\ { c () b } > <<b g >> <<b e >> ~ <<b e >> a }

Again, you might need to play with the trasnsparency property of NoteHead, Stem 
or Beam to make this work for you, and if you do, remember to turn it back on 
again
using the \revert capability.  (Also note that \voiceOne and \voiceTwo are 
'reverted' to normal using \oneVoice ... use \voice? and \oneVoice as a bracket 
around
the notes in question.)

Hope this helps
/Hans