this post was submitted on 23 Oct 2025
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[–] HexesofVexes@lemmy.world 16 points 2 weeks ago (3 children)

So the traditional answer here is to ask them to point at the door the other guard will say is safe.

However, I'm curious, does anyone know of any other valid solutions?

[–] EntirelyUnlovable@lemmy.world 30 points 2 weeks ago (3 children)

"Is the guard that tells the truth standing in front of the safe door?" If they say yes, you go through their door, if they say no then you go to the other one

[–] SmilingSolaris@lemmy.world 6 points 2 weeks ago

I did not think this was going to work. Som bitch it does. Crazy

[–] JargonWagon@lemmy.world 3 points 2 weeks ago

That's wild that this works. What.

[–] PetteriSkaffari@lemmy.world 2 points 2 weeks ago* (last edited 2 weeks ago) (1 children)

If they say yes they can still be a liar.

[–] entropicdrift@lemmy.sdf.org 5 points 2 weeks ago* (last edited 2 weeks ago) (1 children)

Right, in which case the door they're in front of is the safe door because they lied and said "Yes" when asked if the truth teller is in front of the safe door. And if they tell the truth and say yes, they're still the person in front of the safe door. By asking it that way they make it so it doesn't matter if they're the liar or not. "Yes" means that person's door is safe and "No" means you want the other door, no matter who you ask.

[–] PetteriSkaffari@lemmy.world 3 points 2 weeks ago

I was thinking: he could lie about the guard but not about the safe door, so he would still be lying. But that's technically a half-truth, which this particular guard isn't capable of. So you're absolutely right, thank you.

[–] Cargon@lemmy.ml 2 points 2 weeks ago

Could probably do something clever with XOR.

Is exactly one of the following statements true? You are the liar. Your door is the safe door.

[–] Mechaguana@programming.dev 1 points 2 weeks ago (2 children)

How is that a valid answer, they would both point at a different door

[–] zarkony@lemmy.zip 8 points 2 weeks ago (1 children)

They will both point to the bad door.

If asking the thruthful guard, he will point to the door the liar says is safe, which would be the bad door. If asking the liar, he would consider what the thruthful guard says is safe, then reverse that answer, still ending up on the bad door.

They cancel out, so whichever guard you ask doesn't matter.

[–] Mechaguana@programming.dev 1 points 2 weeks ago (1 children)

Wouldnt they instead keep pointing like clockwork towards different doors seeing that they would have to adjust for the other guard?

[–] ChairmanMeow@programming.dev 2 points 2 weeks ago

No because them pointing at a door is answering a different question than the one that was posited in the question.

[–] MajorasTerribleFate@lemmy.zip 6 points 2 weeks ago* (last edited 2 weeks ago) (1 children)

The liar, knowing the truth-teller will point to the good door, points to the bad door.

The truth-teller, knowing the liar would point to the bad door, points to the bad door.

Either way, you take the one your guard doesn't point to.

[–] Mechaguana@programming.dev 1 points 2 weeks ago (2 children)

But they would have to keep adjusting since they both have to answer acco4ding to what the other one says

[–] _AutumnMoon_@lemmy.blahaj.zone 3 points 2 weeks ago

no because the question was which door would the other person say is safe, they both point to the not safe door

[–] Buddahriffic@lemmy.world 1 points 2 weeks ago

The answer is stable because the liar will always say the bad door is safe and the truth teller will always say the safe door is safe, therefore the liar will always say that the truth teller will direct you to the danger door and the truth teller will tell you the same.

I tried to add some self-reference to the question to make a paradoxical answer but can't see a wording that even causes something like "this statement is false", at least not one about which door to pick.

Only ways I can think of start with the paradox right in the question. Like "If the other guard said, 'this statement is false', would you believe him?"

Sucks someone downvoted just for asking questions to better understand this less than straightforward thing. I've always believed that if you think something is wrong, you should challenge it, because even if you are wrong, the resulting discussion can help you understand why your previous perspective was flawed, which might then cascade to other things you didn't realize you were also mistaken about.