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Ramsey property and block oscillation stability on normalized sequences in Banach spaces
Banach Journal of Mathematical Analysis ( IF 1.1 ) Pub Date : 2021-05-07 , DOI: 10.1007/s43037-021-00130-0
A. C. Hernandez-Soto , S. Garcia-Ferreira

A well-known application of the Ramsey Theorem is the proof of the Brunel–Sucheston Theorem. Based on this application, as an intermediate step, we consider the concept of \((k,\varepsilon )\)-oscillation stable sequence, which is generalized with the notion of \(((\mathcal {B}_i)_{i=1}^k,\varepsilon )\)-block oscillation stable sequence where \((\mathcal {B}_i)_{i=1}^k\) is a finite sequence of barriers on \(\mathbb {N}\). We prove that the Ramsey Theorem is equivalent (i.e., one result is deduced by using the other) to the statement:

  • “for every finite sequence \((\mathcal {B}_i)_{i=1}^k\) of barriers, every \(\varepsilon >0\) and every normalized sequence \((x_i)_{i\in \mathbb {N}}\) there exists a subsequence \((x_i)_{i\in M}\) that is \(((\mathcal {B}_i\cap \mathcal {P}(M))_{i=1}^k,\varepsilon )\)-block oscillation stable”,

where \(\mathcal {P}(M)\) is the power set of the infinite set M. We also prove a theorem like the Brunel–Sucheston Theorem which introduces the notion of \((\mathcal {B}_i)_{i\in \mathbb {N}}\)-block asymptotic model of a normalized basic sequence where \((\mathcal {B}_i)_{i\in \mathbb {N}}\) is a sequence of barriers. This notion includes the notion of spreading model of Brunel–Sucheston and we provide an example of a block asymptotic model that is not a spreading model. Moreover, we observe that some of our main results are equivalent to the Ramsey Theorem.



中文翻译:

Banach空间中归一化序列的Ramsey性质和块振动稳定性

拉姆西定理的一个著名应用是布鲁内尔-休斯顿定理的证明。基于此应用,作为中间步骤,我们考虑\((k,\ varepsilon)\)-振荡稳定序列的概念,该概念用\(((\ mathcal {B} _i)_ { i = 1} ^ k,\ varepsilon)\) -块振荡稳定序列,其中\((\ mathcal {B} _i)_ {i = 1} ^ k \)\(\ mathbb { N} \)。我们证明了拉姆西定理与该语句是等价的(即,一个结果可通过使用另一个推论得出):

  • “对于 障碍的每个有限序列\((\ mathcal {B} _i)_ {i = 1} ^ k \) ,每个 \(\ varepsilon> 0 \) 和每个规范化序列 \((x_i)_ {i \在\ mathbb {N}} \) 中存在一个子序列 \((x_i)_ {i \ in M} \) \(((\ mathcal {B} _i \ cap \ mathcal {P}(M)) _ {i = 1} ^ k,\ varepsilon)\) -稳定的振荡”

其中\(\ mathcal {P}(M)\)是无限集M的幂集。我们还证明了一个类似Brunel–Sutston定理的定理,它引入了\((\ mathcal {B} _i)_ {i \ in \ mathbb {N}} \)的概念-归一化基本序列的块渐近模型,其中\ ((\ mathcal {B} _i)_ {i \ in \ mathbb {N}} \}是障碍的序列。该概念包括Brunel–Sutston的扩展模型的概念,我们提供了一个非渐进模型的块渐近模型的示例。此外,我们观察到我们的一些主要结果等同于拉姆西定理。

更新日期:2021-05-07
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