\version "2.4.2"

global = {
 \time 4/4
 \key c \major
}

dessus = \relative c' {
 r4 g'4 fis4 g4
 % 35 :
 d4 g4. f8 [ e8 d8 ]
}

basse = \relative c {
 \stemDown
 fis4 g4 d4 g4 ~
 % 35 :
 g8 [ f8 e8 d8 ] c2
}

choraltheme = \relative c {
 d'1
 % 35 :
 % the following instruction does nothing ; why ?
 g,1
}
\score {
   {
     \context PianoStaff <<
   \context Staff = "dessus" <<
     \global
     \clef violin
     \dessus
   >>
   \context Staff = "basse" <<
     \global
     \clef bass
     \context Voice = "basse" { \voiceTwo \basse }
     \context Voice = "choral" { \voiceOne \choraltheme }
   >>
     >>

     \bar "|."
   }
   \layout {}
   \midi{ \tempo 4 = 100  }

}