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# Truthteller and Liar

You played a long role-playing treasure-hunting game for several hours and finally reached end of the last level of the game. You see two doors ($A$ and $B$), and your treasure is behind one of two doors. Behind the other door is a big monster.

Beside the doors, there are two people ($a$ and $b$ respectively). Both of them know which door has the treasure, and which door has the monster. One is a truthteller (always tells the truth), and one is a liar (always lies). But you don’t know who is who. You can only ask one question to one of them.

• Your goal is to figure out correctly which door has the treasure, based on their answer. What question do you ask, and which person do you ask ?
Level:
Source: folklore
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posted Jun 20 '12

Shiva Kintali
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http://www.cs.princeton.e...
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Posted: Jun 20 '12

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Last updated: Jun 20 '12