leadsheet with intro an lyrics

[Sebastian Menge]

Hi all

I'm writing a leadsheet with chords and lyrics. How can I let the
lyrics start after 4 bars of "intro"? At the moment my score looks
like that:

\score { 

{ <<
  \chords { ... }
  \relative c' { ... }
>>

<<
  \chords { ... }
  \relative c' { ... }
  \addlyrics { ... }
>> }

\header { ... } 

\layout { ... } 

}

But then the second part starts a new staff. How can I prevent that?

Thanks, Sebastian.