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

Correct it isnt the paradox, that is what I get for trying to think of solutions for logic so late at night....But here is another view on Robby's solution:

"If the opposite of a knight is a liar and the opposite of a lie-first knave is a truth-first knave, what would your opposite have answered if I would have asked him/her which route does not lead home instead of this question ?"

If a Liar were to lie, he would not answer the opposite of himself, but as himself.  As he would normally have answered the route that would lead home (as the question was for the route that did not lead home), he would provide the answer for the route that did not lead home.

The Knight would answer the question what the opposite would have answered for the question, and not take into consideration that the Liar would lie about how his opposite would have answered. And thus would have provided the answer as the route that would lead home.

Without knowing the native as Liar, Knight or Knave, the route that leads home is still unknown.

Posted by Dej Mar on 2006-05-25 00:28:03