You are on the island of Knights and Liars exploring an ancient monastery. The old, worn guidebook that the abbot loaned has helped you navigate the catacombs and find all of the interesting old crypts. You are heading back out to garden, still following your guidebook, when you come to a pair of ornately carved doors.

The guidebook describes the two doors: "At this point there are two doors. One will return you to the garden. You must be careful not to open the other door, because beyond it is a sheer drop into the cesspit. The ladder that the monks used to access the chamber was removed when the new wing of the abbey was built with modern plumbing.. Carved on each door in the ancient language is its destination. The door to the garden is marked...."

At this point, the page is torn. You think to yourself, "maybe, if I'm very careful...." but when you look at the doors, you see that the way they are constructed, you cannot open a door without stepping through.

You are about to despair when you hear approaching footsteps. Someone is coming! A monk comes into view. He is wearing a red sash and carrying a basket of food. You remember the ceremony you watched this morning., and realize that he is headed for a meditation chamber deep in the catacombs and will remain there for three days. So much for just following him out.

You remember that the Abbot (a Knight) told you that during the time of their purification, monks are under a vow of near silence. They areallowed to speak only one word per day, in answer to a yes-or-no question. But they must speak it in the ancient language. You remember that "Zim" is one of the words, but you don't remember whether it is "yes" or "no." (Although you can't remember it, the other word is "Dahl.")

Can you ask one question and learn which door to take without knowing either whether the monk is a Knight or a Liar, or whether "zim" means "yes" or "no"?

This puzzle is, I believe, original to me. It was influenced by the books of Raymond Smullyan, which I haven't read in many years. If this should prove to be a re-working of one of his puzzles, I apologize.

(In reply to re(2): Close but.... by levik)

I was thinking about this today after I posted my original solution. I mean, you can pretty easily use this kind of technique to solve the old "Two people in front of two doors. One is a liar, the other a knight. You need to find the exit. What do you say?" puzzle. In fact, one of the people isn't needed at all with this method.

Most about any puzzle where your solution is 'what do you say to them' could be phrased in such a way...

I tried to veer away from the "What will you answer if I ask you..." kind of questioning, as I feel that's cheating just a little too much. I feel a "Will you answer Yes if I ask you..." kind of question is pretty much valid, though... ;-) Plus it worked quite nicely with this puzzle. :-)

Posted by Nick Reed on 2002-06-25 15:04:12