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arXiv math/9308222math.LO
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关于一致反对称函数

On uniformly antisymmetric functions

Peter Komjath, Saharon Shelah

摘要:

证明了如果A的子集R是可数的,则总有一致反对称f:A-> {0,1}.我们证明了连续统假设等价于存在一个f:R-> omega,其中对R中的每个x,|S_x| <= 1.如果连续统至少是aleph_n,则存在点x使得S_x至少有2^n-1个元素。我们还证明了存在函数f:Q-> {0,1,2,3}使得S_x总是有限的,但不存在这样的函数在R上具有有限值域

英文摘要:

We show that there is always a uniformly antisymmetric f:A-> {0,1} if A subset R is countable. We prove that the continuum hypothesis is equivalent to the statement that there is an f:R-> omega with |S_x| <= 1 for every x in R. If the continuum is at least aleph_n then there exists a point x such that S_x has at least 2^n-1 elements. We also show that there is a function f:Q-> {0,1,2,3} such that S_x is always finite, but no such function with finite range on R exists

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