Which door leads to freedom?

On the king’s birthday, a prisoner is led into the royal presence. The king says, “You see two doors before you. One leads to freedom, the other to the gallows. In front of each door is a guard, who either always tells the truth or always lies. You may ask one guard one question. Then you must pick your door.” Which question should the prisoner ask?

Today’s deal reminded me of this problem because it made me think of doors. How should South plan the play in six spades after West leads the club jack?

If the trumps are 4-0, the contract cannot be made. However, assuming a 2-2 or 3-1 spade break, there appear to be 12 easy tricks: five spades, three hearts, one diamond and three clubs. Did you spot the snag, though? You are in the dummy for the last time. There is no second door to give you a reentry to the dummy. If you play a trump immediately, you will lose two diamond tricks.

You must use your entry wisely and hope for friendly distribution. Start with dummy’s three top clubs, evicting the heart king and ace! Then cash dummy’s three heart winners, throwing diamond losers onto the discard pile. If no one has inconsiderately ruffed in, draw trumps and concede a diamond trick.

The prisoner should ask either guard, “If I ask you, ‘Is this the door to freedom?’ will you say ‘Yes’?” If the guard replies “Yes,” the prisoner goes through that door. If the guard answers “No,” the prisoner goes through the other door. With the guard who lies, it is the classic double negative giving an affirmative.