\version "2.18.2"
\new Staff {
  \relative c'' {
    <<
      {
        b4 a <b c> b
        <b c>4 a \once \voiceTwo c b
        c2
      } \\ {
        a4 b a <g a>
        <g a>4 c \voiceFour e \voiceThree g,
        \voiceTwo c4
      }
    >>
  }
}