\version "2.15.13"

%Fonction Scheme transformant une barre de mesure  ".|" en crochet \StaffGroup
startBracket = {
  \once \override StaffGroup.BarLine #'stencil = %essai avec Staff.Barline ou Score.Barline
	#(lambda (grob)				 ; -->autre résultat mais pas satisfaisant non plus
	  (ly:stencil-add
	    (ly:stencil-combine-at-edge
	      (ly:bar-line::print grob)
	      Y UP
	      (grob-interpret-markup grob (markup
	        #:musicglyph "brackettips.up"))
	      -0.1)
	    (ly:stencil-combine-at-edge
	      (ly:bar-line::print grob)
	      Y DOWN
	      (grob-interpret-markup grob (markup
	        #:musicglyph "brackettips.down"))
	      -0.1)
            ))	  
	\bar ".|"
}
sop  = { \set Score.timing = ##f 
         \repeat unfold 3 { a'4 a' a' b' b' b' } \break \bar "|"
         a'4 a' a' b' b' b'
         \startBracket
         c'' c'' c'' c''  \bar "|."
}
alt = { \repeat unfold 3 { f'4 f' f' f' f' f' }
        s2. s2.
        f'4 f' f' f'
}
ten = { \repeat unfold 3 { d'4 d' d' d' d' d' }
        \stopStaff 
        \override Staff . Clef #'transparent = ##t  
        \override Staff.TimeSignature #'stencil = ##f
        s2. s2.
        \startStaff
        \override Staff . Clef #'transparent = ##f
        \once  \override Score.BreakAlignment #'break-align-orders =
                #(make-vector 3 '(staff-bar clef )) 
        \set Staff.forceClef = ##t
        c'4 c' c' c'
}
bas = { \repeat unfold 3 { d4 d d d d d }
        s2. s2.
        d4 d d d
}
\context StaffGroup <<
  \override StaffGroup.SystemStartBracket #'collapse-height = #1 % Ces 2 lignes permettent des crochets meme pour une seule portée
  \override Score.SystemStartBar #'collapse-height = #1

\context Staff ="upper"
<<
\clef treble
\time 3/4
\context Voice = "one" { \voiceOne << \sop   >> } 
\context Voice = "two" { \voiceTwo << \alt  >> } >>

\context Staff ="lower"
<<
\clef bass
\context Voice = "one" { \voiceThree << \ten >> } 
\context Voice = "two" { \voiceFour << \bas >>  }  >> 
>>