02 January 2011

Double dummy

Along with the hand records our dealing machine adds a double dummy analysis of the contracts available. I'm not sure if it uses Deep Finesse or one of the myriad other solvers that have appeared but no one has been able to fault it so far. The most common 'use' for this wee feature is for beginner and intermediate players to look at it and say "Look it says we should be in 3! How do we bid that?".

What I enjoy is the hand that comes along every so often where it appears that the double dummy is wrong. The time spent working out just how it does what it does is fun especially with a few people to help throw in ideas. Even better when the double dummy result is the intuitive one until someone challenges it and then you have to prove they're wrong:

Contract: 4
by South
8 3
T 8 5
T 9 5 3
A 8 6 4
Q J 9 7 3 2
Q 8 7 6
T 9
Q 9 6 4
A K J 2
7 3 2
A K J T 5 2
6 4
K Q J 5

On this hand the double dummy solvers will testify that you cannot make 10 tricks in spades. This is intuitively correct because you have 3 red losers and you're an entry to dummy short to finesse twice in spades.

Look though at the doubleton T9 in the same hand as the short spade! Surely you can ruff at trick four and overtake the K to take the first spade finesse. Then cash a club, enter the dummy by the 8 and take that second so desperately needed hook. Good point.

However just like double dummy declarers make it look easy double dummy defenders make it impossible. First the defence start with two rounds of hearts followed by a sneaky under lead in diamonds to get back to the West hand. West nonchalantly plonks a big heart on the table allowing East to pitch a club. That critical club pitch ruins the clever line above and you're back to the 9 tricks it always looked like there were.

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