求翻译：there are some people in a room. Each of them is wearing a hat. Some are white,the others are black. People can just see others' hats but they don't know what themselves are wearing. Then they turn off the light. If someone thinks he is wearing black hat,he will slap himself in the face . First time they turn off the light ,but it is quiet. So they turn on the light again. After a minute ,they turn off the light ,but it is still quiet.The third time they turn off the light ,someone slaps himself in the face .是什么意思？

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