[bonanova]

I heard this posed [not original with me] and I have not worked out a solution. Yet.

A truthful person who is aware of every fact will answer yes/no questions in a certain way.

Curiously, a liar who is misinformed about every fact will answer yes/no questions in exactly the same way!

If you asked: "Is the sky blue?" both would answer: "Yes."

The first, because he knew it to be true and answered truthfully according to his belief.

The second, because he believed it to be false and lied according to his belief.

The puzzle is this:

Can you distinguish between the two by asking a series of yes/no questions?

If so [and why would we ask if you couldn't? ] what is the minimum number of questions needed?

[Guest]

Too "bonanova" (I don't know how to use quote ):

The simplicity in them both telling you the objective truth is in the fact that you can directly ask them the simplest question "are you a liar?, are you truthfull? is the other guy a liar?,...", for the truth teller will give you the truth, and the liar will give you HIS lie, making it in fact a truthful fact because of his total misinformation, that's what I meant when I said it was a bit too easy. It's similar to a different version, I can't remeber it completely, but it had something to do, with you walking on the road coming to a crossroad and there were two paths but only one was right and there were a liar and a truthteller standing, so you had to find out which was the right path by asking them questions (I don't know if they have to be yes/no questions)

End.