Joke: Three logicians walk into a bar!
Three logicians walk into a bar. The bartender says "Do you all want something to drink?"
The first logician says "I don't know."
The second logician says "I don't know."
The third logician says "Yes."
(Explanation: The first and second knew that they wanted a drink but didn't know what the following logician would want, so they couldn't be certain that they would all want one. When it got to the third logician he was able to confirm it because neither of the other two had said no.)
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