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Apr 13, 2010 at 21:57 history edited Cam McLeman CC BY-SA 2.5
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Apr 13, 2010 at 21:57 comment added Cam McLeman Ah, good point. Interesting.
Apr 13, 2010 at 21:04 comment added Qiaochu Yuan You can delete the word "known": the two are equivalent, since if there's at least one prime in every arithmetic progression then given an arithmetic progression a mod n, there's a prime congruent to a+n mod n^2, a prime congruent to a+n^2 mod n^3, etc.
Apr 13, 2010 at 17:01 comment added villemoes A good example of such a puzzle is this: Let x = sqrt(2) and y = 2+sqrt(2). Let X be the set { floor(nx) | n a positive integer }, and define Y similarly. Prove that X and Y are disjoint, and that their union is the set of positive integers. The not-so-obvious key is that x and y are (positive) irrational numbers satisfying 1/x + 1/y = 1; and in fact the statement holds (and is easier to prove) for all such pairs.
Apr 13, 2010 at 16:39 history edited Cam McLeman CC BY-SA 2.5
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Apr 13, 2010 at 16:38 history made wiki Post Made Community Wiki by Ben Webster
Apr 13, 2010 at 16:09 comment added Sunni When we come across a (rearch) problem, sometimes we may not see its full picture. And in each step for a good theorem, we may not need their full generality, but a special case is enough.
Apr 13, 2010 at 15:49 history answered Cam McLeman CC BY-SA 2.5