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| | π: MATH Pages of Jonathan Vos Post |
 | | That problem was the Four Nines Puzzle, based on the even older Four Fours Puzzle, which is also discussed on this web page. |
| | The problem of whether two strings of characters evaluate to the same integer is a very hard problem, in terms of the amount of computation necessary to determine it in general, called the "word problem" in complexity theory. |
| | In this book the "Four Fours Problem" is called a "traditional recreation." There are several fine sites on the World Wide Web for "Four Fours Problem." But I recommend to the reader: "Mathematical Games", by Martin Gardner, [Scientific America, Jan 1964]. |
| www.magicdragon.com /math.html (4600 words) |
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