\version "2.19.82"
\language "english"

remove-if-sibling = #(define-scheme-function (offsets) (list?)
           (lambda (grob)
             (let* (
                     ;; The parent of a VerticalAxisGroup is a VerticalAlignment
                     (parent (ly:grob-parent grob 1))
                     ;; Get the children VerticalAxisGroups of the parent
                     (siblings (ly:grob-object parent 'elements))
                     (siblings-list
                      (if (ly:grob-array? siblings)
                          (ly:grob-array->list siblings)
                          '()))
                     ;; Find the siblings above or below me by offsets
                     (my-vindex (ly:grob-get-vertical-axis-group-index grob))
                     (enemy-indices (map (lambda (offset) (+ offset my-vindex)) offsets))
                     (enemy-vaxis? (lambda (v) (member (ly:grob-get-vertical-axis-group-index v)
                                                 enemy-indices)))
                     (enemy-vaxes
                      (filter enemy-vaxis? siblings-list))
                     )
               ;; Suicide if an enemy sibling is alive
               (map
                (lambda (enemy-vaxis)
                  (ly:pointer-group-interface::add-grob grob 'make-dead-when enemy-vaxis))
                enemy-vaxes)
               )
             )
           )

global = {
  s1
  \break
  s1*3
  \break
  s1
  \bar "||"
}

flute = {
  \clef treble
  \set Voice.midiInstrument = "flute"
  R1*3 |
  % Notice that without the hairpin, the Ob. 2 staff doesn't disappear
  c''1\< |
  c''1 <>\! |
}

oboeI = {
  \clef treble
  \set Voice.midiInstrument = "oboe"
  \context Staff = "Ob1" { \unset Staff.keepAliveInterfaces }
  R1 |
  c''1 |
  R1 |
  \context Staff = "Ob1" { \set Staff.keepAliveInterfaces = #'() }
  R1*2 |
}

oboeII = {
  \clef treble
  \set Voice.midiInstrument = "oboe"
  R1*2 |
  c'1 |
  R1*2 |
}

\score {
  <<
    \new Staff = "Fl1" \with {
      instrumentName = "Flute"
      shortInstrumentName = "Fl."
    } << \global \flute >>
    \new StaffGroup \with {
      instrumentName = "Oboe"
      shortInstrumentName = "Ob."
      systemStartDelimiter = #'SystemStartSquare
      \override SystemStartSquare.collapse-height = #5
    } <<
      \new Staff = "Ob1+2" \with {
        instrumentName = \markup\right-column {"1" "2"}
        shortInstrumentName = \markup\right-column {"1" "2"}
        \override VerticalAxisGroup.before-line-breaking = \remove-if-sibling #'(1)
      } { <> << \global \partcombine \oboeI \oboeII >> }
      \new Staff = "Ob1" \with {
        instrumentName = "1"
        shortInstrumentName = "1"
        \override VerticalAxisGroup.remove-empty = ##t
        \override VerticalAxisGroup.remove-first = ##t
      } << \global \oboeI >>
      \new Staff = "Ob2" \with {
        instrumentName = "2"
        shortInstrumentName = "2"
        \override VerticalAxisGroup.before-line-breaking = \remove-if-sibling #'(-2)
      } << \global \oboeII >>
    >>
  >>
  \layout {
    \context {
      \Score
      \override InstrumentName.self-alignment-X = #1
      \override InstrumentName.padding = #3
    }
    \context {
      \Staff
      \override InstrumentName.padding = 0.3
    }
  }
}