In a nutshell (translating Monty Hall into a Bridge-like situation), if you have chosen the wrong door, Monty only has one choice; he must pick the wrong door. If you had already chosen the correct door, both of his choices would be equally wrong.

Now (here's the tricky part), since he has picked one door, we know that if you are right, he could have picked the other door. Since he didn't pick it, you should. The odds are in your favor if you do.

Too much fun :-)

I looked for a good "Restricted Choice" link, but this was the best I could do on short notice

Russ
Brainbench 'Most Valuable Professional' for Perl