It is solvable. You ask one guard at random, “Which door would the other guard have said leads to certain doom if I had asked them?”
And no matter which guard you ask, go through the door they answer with. If it was the truth teller guard, they’ll tell you which door the liar would have said, and if it’s the liar they’ll lie about which door the truth teller would have said.
Yes, you’re right. I was thinking he could lie both about what the other guard would have said as well as what door leads to doom, but the other guard can only give one truthful answer.
Only one question allowed, they said. I don’t think it’s solvable.
It is solvable. You ask one guard at random, “Which door would the other guard have said leads to certain doom if I had asked them?”
And no matter which guard you ask, go through the door they answer with. If it was the truth teller guard, they’ll tell you which door the liar would have said, and if it’s the liar they’ll lie about which door the truth teller would have said.
Yes, you’re right. I was thinking he could lie both about what the other guard would have said as well as what door leads to doom, but the other guard can only give one truthful answer.