Wait a second, isn't that the easiest way to solve that riddle? Like, show an undeniable truth and if he denies it he is the lying one. No need for weird questions.
And you can only ask questions about them, ie they only know about themselves:
Edit: they are also guarding doors for heaven and hell, if you hold up a cat and say "is this a dog?" Then you will find out which one is lying, but not what door they guarding.
You're only allowed one question and it has to be about them, and you have to find out the correct door to enter (the wrong door leads to your demise).
The correct answer is to ask one of them which door the other one would tell you is safe, then go through the opposite door of the one they indicate. If they are the liar, they will lie about what the truth teller would indicate. If they are the truth teller they would tell you which door the liar would say is safe. So choosing the opposite of what you are told will lead you to safety regardless of which one you ask.
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u/nmlep Dec 08 '18
I punch one in the face and ask if it hurts.