\score
{
  \new PianoStaff
  <<
    \new Staff = "up" {
      <<
        \set Timing.beamExceptions = #'()
        \set Timing.beatStructure = #'(4)
        \new Voice {
          \voiceOne
          \autoChange
          \relative c' {
            g8 a b c d e f g
            g,8 a b c d e f g
          }
        }

        \new Voice {
          \voiceTwo
          \autoChange
          \relative c' {
            g8 a b c d e f g
            g,,8 a b c d e f g
          }
        }
      >>
    }

    \new Staff = "down" {
      \clef bass
    }
  >>
}