STEM COLLISION :: A GOOD (BUT TRICKY) SOLUTION

[MX]

Bonjour à tous, hi all !

Thank you very much, Tapio, Carrick and Erik for your help and your answers.

Thanks to you, here is a pretty good solution to my question. I adapted 
the Tapio's
solution with the Carrick's advice about dot position. See attached file 
compare.png.

Encore merci.

M.X.

% -*- mode: LilyPond ; coding: utf-8 -*-
\version "2.6.4.3"
%\include "italiano.ly" 



\header{
    title = \markup {\center-align { "Offertoire" "extrait du" "Premier livre 
d'Orgue"} }
    subtitle = ""
    piece = "" 
    instrument = ""
    composer = "Jean-François Dandrieu (1681-1738)"
    copyright = "Creative Commons Attribution-ShareAlike 2.5"
    mutopiainstrument = "Organ"
    style="Baroque"
    footer = "Mutopia-2006/??"
   
}

#(set-default-paper-size "a4")

global = {
  \key a \minor
  \time 4/4
}

soprano = \relative c'' {
  << { \once\override Voice.Dots #'extra-offset = #'(0.6 . 0.0) a'8. g16 
g8.\prallprall f16 f4. a,8}\\ 
     {s4 s s s}\\   %this is voice 2, perhaps the "alto" could also be entered 
here
     {\once \override TextScript #'extra-offset = #'(-1.7 . -3.8)  \once 
\override NoteColumn #'force-hshift = #0.4 f'4 ^\markup {\musicglyph 
#"scripts.mordent" }  s s s } 
   >> 
}

alto = \relative c'' {
  c8 d8 e4 <a, c>4. d,8
} 

tenor = \relative c' {
  s1 
} 

basso = \relative c {
  f8 bes8 c8 c,8 f8 g8 a8 fis8 
}

 \paper {
    raggedright = ##t
  }
\score {
  
  \context PianoStaff <<
    \context Staff = "dessus" <<
      \global
      \clef violin
      \context Voice = "soprano" {
        \voiceOne \soprano
      }
      \context Voice = "alto" {
        \voiceTwo \alto
      }
    >>
    \context Staff = "basse" <<
      \global
      \clef bass
      \context Voice = "tenor" {
        \voiceOne \tenor
      } 
      \context Voice = "basse" {
        \voiceTwo \basso
      }
    >>
  >>
  \layout {}
  
  \midi { }
 
}