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THE ℓ1-DICHOTOMY THEOREM WITH RESPECT TO A COIDEAL

机译:关于偶极子的ℓ1-二定理

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In this paper we introduce, for any coideal basis B on the set N of natural numbers, the notions of a B-sequence, a B-subsequence of a B-sequence, and a B-convergent sequence in a metric space. The usual notions of a sequence, subsequence, and convergent sequence obtain for the coideal B of all the infinite subsets of N. We first prove a Bolzano-Weierstrass theorem for B-sequences: if B is a Ramsey coideal basis on N, then every bounded B-sequence of real numbers has a B-convergent B-subsequence; and next, with the help of this extended Bolzano-Weierstrass theorem, we establish an extension of the fundamental Rosenthal's -dichotomy theorem: if B is a semiselective coideal basis on N, then every bounded B-sequence of real valued functions (fn)n∈A has a B-subsequence (fn)n∈B, which is either B-convergent or equivalent to the unit vector basis of ℓ1(B).
机译:在本文中,对于自然数集N的任何理想基础B,我们介绍了度量空间中B序列,B序列的B子序列和B收敛序列的概念。对于N的所有无限子集的共同B,可以获得序列,子序列和会合序列的通常概念。我们首先证明B序列的Bolzano-Weierstrass定理:如果B是基于N的Ramsey共同定理,则每个实数的有界B序列具有B收敛B子序列;接下来,在扩展的Bolzano-Weierstrass定理的帮助下,我们建立了Rosenthal基本二分法定理的扩展:如果B是基于N的半选择共理想基础,则实值函数(fn)n的每个有界B序列∈A具有B子序列(fn)n∈B,它是B收敛的或等效于ℓ1(B)的单位矢量。

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  • 来源
    《Real analysis exchange》 |2017年第1期|167-183|共17页
  • 作者单位

    Department of Mathematics, National and Kapodistrian Athens University, Panepistemiopolis, 15784 Athens, Greece;

    Department of Mathematics, National and Kapodistrian Athens University, Panepistemiopolis, 15784 Athens, Greece;

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