\version "2.17.95"

global = {
  \key bes \major
  \numericTimeSignature
  \time 3/4
}

up = {
  \global
  % Music follows here.
  <<
    \new Voice \relative c'' { \voiceOne
      ees,8[ c'( <\tweak #'font-size #-4 ees, g> f <\tweak #'font-size #-4 c ees> d)]
      ees2. 
    }
    
    \new Voice \relative c'' { \voiceTwo
      c,8[ \change Staff = "down" \stemUp aes] 
        \shape #'((0.9 . 1.9) (0 . 5) (-1.0 . 0) (-1 . 0)) Slur
        g2(
      \change Staff = "up" g2.)
    }
  >>
  }

down = {
  \global
  % Music follows here.
    \new Voice \relative c { \voiceFour
      g4. \stemDown c8[( g ees)] \stemNeutral
      c[ g'( c d ees f)]
    }
}

pianoPart = \new PianoStaff  <<
  \new Staff = "up"  \up
  \new Staff = "down"  { \clef bass \down }
>>

\score {
  \pianoPart
}