摘要：
Friday the ThirteenthIs Friday the 13th really an unusual event?That is, does the 13th of the month land on a Friday less often than on any other day ... 阅读全文
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Greedy Gift GiversA group of NP (2 ≤ NP ≤ 10) uniquely named friends has decided to exchange gifts of money. Each of these friends might or might not ... 阅读全文
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Your Ride Is HereIt is a well-known fact that behind every good comet is a UFO. These UFOs often come to collect loyal supporters from here on Earth. ... 阅读全文