FILE No.181Unsolved
The triplets Mei, Yui, and Rii played a pretend game of angel, devil, and human. An angel says only true things. A devil says only false things. A human may say any mix of true and false things (both true, both false, or one of each). Each person has one role, and each makes two statements.
Choose the correct combination of who plays which role.
If you get stuck, open the hints one at a time, in order.
What goes wrong if Rii is the devil?
An angel says only true things.
Once the devil is decided, the rest is the human.
Choose the correct combination of who plays which role.
Choose the answer closest to the truth.
Rii = angel, Yui = devil, Mei = human
The answer is "Rii = angel, Yui = devil, Mei = human."
If Rii were the devil, "Mei is not the devil" would also be false, making Mei a devil too, which gives two devils. So Rii is not the devil.
Suppose Rii were the human. Then Yui and Mei would be the angel and the devil in some order. But Mei says "I'm the devil": an angel cannot say that (it would be false), and a devil cannot say it either (it would be true). So Rii is not the human, and therefore Rii is the angel. Rii's statements are true, so Mei is not the devil. The devil is Yui, and "I'm the human" is a lie. The remaining one, Mei, is the human. Checking every case also shows that only this combination works.
Because you are unsure how to treat "everything a liar says is false."
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