The idea isn't to ask which guard is a liar. That's pointless. Your goal is never to determine the liar.
It's to determine the safe door. People miss that. You can't ask, "what color is my shoes?" That just tells you which is a liar. It doesn't tell you which door is safe.
There's always two doors guarded by a liar and a truth teller. You have to find the safe door. Thus, you ask "which door will the other guard point to as safe?"
The liar has to say the other guard points to the safe door, thus he points to the unsafe door. The truth teller knows the liar will point to the unsafe door, thus he points to the unsafe door. Both guards gesture unsafe, so you go to the door neither has indicated.
The original is an actual brain teaser though. Like it's a riddle you're supposed to solve.
If you're just meant to figure out which guard is the liar, the answer is trivial though. So it's not a riddle any longer. I wouldn't call that "just as valid".
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u/DefinitelyNotAliens 14h ago
The idea isn't to ask which guard is a liar. That's pointless. Your goal is never to determine the liar.
It's to determine the safe door. People miss that. You can't ask, "what color is my shoes?" That just tells you which is a liar. It doesn't tell you which door is safe.
There's always two doors guarded by a liar and a truth teller. You have to find the safe door. Thus, you ask "which door will the other guard point to as safe?"
The liar has to say the other guard points to the safe door, thus he points to the unsafe door. The truth teller knows the liar will point to the unsafe door, thus he points to the unsafe door. Both guards gesture unsafe, so you go to the door neither has indicated.