Lyrics alignment problem

[Riccardo Orfei]

dear lilypond users,

I am experiencing some trouble in writing lyrics in a song with repeats
and alternatives.
Here is a sample of what I get: the text of this simple song is being
displayed on three lines.
What am I supposed to do to have my text on a single line?

Thank you for your kind attention,
Ric


\version "2.4.0"
\include "italiano.ly"
% tilde = ~
global = { \time 4/4 \key mib \major }
%
aaaa = \relative { do re mi fa }
bbbb = \relative { sol' la si do }
cccc = \relative { do' si la sol }
%
lyaaaa = \lyricmode { do re mi fa }
lybbbb = \lyricmode { sol la si do }
lycccc = \lyricmode { do si la sol }
%
\score {
<<
\new Staff {
\repeat volta 2 { \context Voice = "voice" { \aaaa } }
\alternative { \context Voice = "altI" { \bbbb }
\context Voice = "altII" { \cccc }
}
}
\lyricsto "voice" \new Lyrics \lyaaaa
\lyricsto "altI" \new Lyrics \lybbbb
\lyricsto "altII" \new Lyrics \lycccc
>>
\layout { }
\midi { \tempo 4=90 }
}