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arXiv 0903.4957math.LO
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无界度量结构的连续一阶逻辑

Continuous first order logic for unbounded metric structures

Itaï Ben Yaacov

摘要:

我们提出了一个适应的连续一阶逻辑无界度量结构。它的优点是在精神上更接近C。Ward Henson的逻辑对于巴拿赫空间结构比单位球方法(这是迄今为止连续逻辑中巴拿赫空间结构的常用方法),以及在单位球方法不适用的情况下的应用(即,当单位球不是可定义的集合时)。我们还介绍了过程的单点\emph{emboundment}(密切相关的拓扑单点紧化),使无界结构回到有界连续一阶逻辑的设置。连同结果从\cite{BenYaacov:Perturbations}关于扰动的有界度量结构,我们证明了一个Ryll-Nardzewski风格的表征理论的巴拿赫空间这是可分范畴的小扰动的规范。这最后一个结果是由Henson的一个未发表的结果激发的。

英文摘要:

We present an adaptation of continuous first order logic to unbounded metric structures. This has the advantage of being closer in spirit to C. Ward Henson's logic for Banach space structures than the unit ball approach (which has been the common approach so far to Banach space structures in continuous logic), as well as of applying in situations where the unit ball approach does not apply (i.e., when the unit ball is not a definable set). We also introduce the process of single point \emph{emboundment} (closely related to the topological single point compactification), allowing to bring unbounded structures back into the setting of bounded continuous first order logic. Together with results from \cite{BenYaacov:Perturbations} regarding perturbations of bounded metric structures, we prove a Ryll-Nardzewski style characterisation of theories of Banach spaces which are separably categorical up to small perturbation of the norm. This last result is motivated by an unpublished result of Henson.

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