\layout {
    \context {
        \PianoStaff
            \consists #Span_stem_engraver
    }
}

PartPOneVoiceOneBIS =  \relative c' {
  \clef "treble" \key c \major \time 4/4

  % \override Stem.cross-staff = ##t
  %  \override Stem.length = #19 % this is in half-spaces,
  % so it makes stems 9.5 staffspaces long
  %  \override Stem.Y-offset = #-6 % stems are normally lengthened
  % upwards, so here we must lower the stem by the amount
  % equal to the lengthening - in this case (19 - 7) / 2
  % (7 is default stem length)

  %  \override NoteColumn.ignore-collision = ##t

  R1 | % 2
  r4
  %\once \override Stem.direction = #LEFT
  \stemDown \autoBeamOff
  \crossStaff {
      c8
      <c e g>8
  }
  r2
  \bar "|."
}

PartPOneVoiceTwoBIS =  \relative a {
  \clef "bass" \key c \major \time 4/4 | % 1

  a8 [
  \change Staff="1"
  e'8
  \change Staff="2"
  a,8
  \change Staff="1"
  e'8 ] c'8 [ e,8
  \change Staff="2"
  a,8 b'8 ] <c,, e g c>8 [
  \change Staff="1"
  <c' e g>8
  \change Staff="2"
  <c, e g>8
  % \change Staff="2"
  g'8 ]
  % \change Staff="2"
  r2 \bar "|."
}


% The score definition
\score {
  <<
    \new PianoStaff
    <<
      \context Staff = "1" <<
        \context Voice = "PartPOneVoiceOne" {  \PartPOneVoiceOneBIS }
      >>

      \context Staff = "2" <<
        \context Voice = "PartPOneVoiceTwo" {  \PartPOneVoiceTwoBIS }
      >>
    >>
  >>

  \layout {}
  % To create MIDI output, uncomment the following line:
  %  \midi {\tempo 4 = 100 }
}

%%%%%%%%%%%%%