[Russian] математический анекдот (исправил ошибку)

В книге Paul Hoffman'а The Man Who Loved Only Numbers: The Story of Paul Erdos and the Search for Mathematical Truth имеется такая байка:

For all of Kummer's work on the cutting edge of number theory, he was apparently rather bad at elementary arithmetic. One story has him standing before a blackboard. trying to compute 7 times 9. "Ah," Kummer said to his high school class, 7 times 9 is eh, uh, is uh. . .."61," one of his students volunteered. "Good," said Kummer, and wrote 61 on the board. "No," said another student, "it's 69." "Come, come, gentlemen," said Kummer, "it can't be both. It must be one or the other." (Erdos liked to tell another version of how Kummer computed 7 times 9: "Kummer said to himself, 'Hmmm, the product can't be 61 because 61 is a prime, it can't be 65 because that's a multiple of 5, 67 is a prime, 69 is too big—that leaves only 63.' ")

Это напоминает анекдот, который я врядли смогу выразить на английском.

Урок по математике в грузинской (извините) школе.

Учитель: так, Васо, сколько будет дважды четыре?

Васо: девять!

Учитель (задумался): нет, нет... (и отогнал от себя эту мысль).. это слишком много! А ну ты, Гиви, сколько будет дважды четыре?

Гиви (двигая ладонью в воздухе): семь-восемь...

Учитель (задумчиво, тоже двигая ладонью): да, где-то так, семь-восемь... но никак не девять!

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