Negative Slam Doubles
---------------------

After a competitive auction where the opponents land in a slam and 
you and partner have raised a suit preemptively, a double by the 
immediate hand after the slam bid shows 0 defensive tricks.  Partner
leaves it in with 2 tricks or sacrifices with 0 or 1 trick.

With 1 or more tricks, the immediate hand after the slam bidder 
passes.  With 0 tricks, partner doubles which the first partner can
leave in with enough setting tricks OR take out for a sacrifice.  
With 1 or more tricks, partner passes.  

Why should partner pass?  Well, if your partner does have 1 trick
and you have 1 trick then the opponents are down in a slam-- which
should be a good score in matchpoints since most of the other 
players will be making their game contracts.