You are lost once again in the land of Knights, Knaves, and Liars, and once again you find yourself at a fork in the road. You know that one path will lead you to a safe return home, while the other will lead you to your own gruesome demise. (You really need to find a better vacation spot next year!)

Standing at the fork is a native, who might be either a Knight (who always tells the truth), a Knave (who alternates between true and false statements), or a Liar (who always lies). You have no way of knowing which he is. Worse yet, you realize that if he is a knave, you don't know if he will tell you the truth first, and then lie, or lie first and then tell the truth, etc.

What is the fewest number of questions you have to ask to find out which is the safe road, and what are they?

(In reply to re(3): The jury isn't in. (re: question and solution) by Venkat)

A more logical answer to why the single question posed by Robby is not sufficient.

Because of the condition given, a Liar could base his answer as if he were a lying Knave, a truth-telling Knave or even as a Liar as this would be a lie to that of the condition imposed, and then lie about what his opposite (as he chose to represent) would say.

“Liars always lie about everything.”

Therefore, in order for the Knight or truth-first Knave to answer the question truthfully, he/she would have to respond with “I don’t know.” As “I don’t know” does not reveal the direction that  should be travelled, the question alone does not provide a safe solution.

Edited on May 25, 2006, 5:09 am

Posted by Dej Mar on 2006-05-25 01:56:54