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Strange Symmetric Sickness (Posted on 2007-04-13) Difficulty: 3 of 5
A strange epidemic affected about half the population of a Liars and Knights island. The sickness was strange: sick liars behaved as knights and always told the truth, while sick knights behaved as liars and lied all the time.

During that time, there was a theft, and a judge confronted the three suspects: Jacob, Karl, and Louie. It was a sure thing that one of them was guilty, and also that the two innocent ones knew perfectly well who was the guilty one.

The judge asked Jacob: "What do you know about the theft?". Jacob answered "The thief is a liar". The judge then asked him "Is he healthy or sick?", and Jacob answered "He is healthy".

The judge then asked Karl: "What do you know about Jacob?", and Karl answered "He is a liar". The judge asked "Healthy or sick?", and Karl added "Jacob is sick".

The judge thought for a while, and then asked Louie "Are you the thief?". Louie answered (yes or no), and the judge decided the case.

Who was the thief?

I got this problem from a book by Raymond Smullyan.

See The Solution Submitted by Old Original Oskar!    
Rating: 4.3333 (3 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
Hints/Tips Initial Ramblngs (part spoiler) | Comment 1 of 3
From Karl we learn that Jacob is a Sick Liar or a Healthy Knight.
In either case he is a Truth Teller.
Thus the thief is a Healthy Liar - and not Jacob.
Now where to??

  Posted by Vernon Lewis on 2007-04-13 14:56:47
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