tie on first and second! alternative?

[Albert Einstein]

I want to obtain a tie that joins the last chord  before first 
alternative  with identical  chord in first and second alternative.

< a b c>~   \alternative {  {  <a  b  c>  } {  < a  b  c>  }  }
This above  command produces only a tie between the chord before first 
alternative and the chord in first alternative.
How can I obtain the tie between the chord and second alternative ?

Albert