\version "2.14.0"
texidoc = " The space engine preserves by default the space for the
empty sections of lyrics, so that the lines remain consistently spaced.

When you want to use a separate @code{Voice} context for each
singer, even though the melodies usually don't overlap, you might want
to let interrupted lyrics collapse to a single line.

The layout overrides may still be useful for scores where there is
occasional small overlap between the voices, though.

In order to easily identify who sings, one of the lyrics may be
displayed in italics.
"
doctitle = "Combining lyrics"

\layout {
  \context {
    \Lyrics
    \override VerticalAxisGroup #'nonstaff-nonstaff-spacing
       #'minimum-distance = ##f
    \override VerticalAxisGroup #'nonstaff-unrelatedstaff-spacing
       #'minumum-distance = ##f
    \override LyricText #'minimum-Y-extent = #'(-0.6 . 2.0)
  }
}

<<
  \new Staff <<
    \new Voice = "mum" { f'4^"mum" g' r2 | s1 | \break a'2 g' | f'1 }
    \new Voice = "dad" { s1        | a'2^"dad" g' | e'1 }
  >>
  \new Lyrics \lyricsto "dad" \lyricmode {
    \override LyricText #'font-shape = #'italic
    may -- be... to -- mor -- row }
  \new Lyrics \lyricsto "mum" \lyricmode { let's say now }
>>