Legend has it that a certain college philosophy professor asked one question on his final exam. He picked up a chair, put it on his desk, and wrote on the board, “Using everything we have learned this semester, prove that this chair does not exist.”
The students dug deep and wrote like crazy for a while hour, some of them churning out 30 pages of heady philosophical debate and logic. But one student turned in his paper after less than a minute and he was the only one to get an “A.”
What did he write so quickly that turned out to be just the right answer?