\version "2.18.2"

\parallelMusic #'(voiceA voiceB) {
  ges'4 ges4	|
  r8 gis r8 gis	|
}

\new PianoStaff \relative c' <<
  \accidentalStyle piano
  \new Staff { \voiceA }
  \new Staff { \voiceB }
>>