\paper {
  #(set-paper-size "a6landscape")
  line-width = 120
  ragged-right = ##f
}

<<
  \new Staff <<
    \new Voice = vvvb {
      \relative {
        c' d4. e8 f4
        f g4.. a16 b4
      }
    }
    \new Lyrics \lyricmode {
%%      \set associatedVoice = vvvb
      abcd abcd4. abcd8 abcd4 abcd abcd4.. abcd16 abcd4
    }
  >>

  \new Staff <<
    \new Voice = vvvc {
      \relative {
        c' d e f
        f g a b
      }
    }
    \new Lyrics \lyricmode {
%%      \set associatedVoice = vvvc
      abcd abcd abcd abcd abcd abcd abcd abcd
    }
  >>
>>