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arXiv 1702.02702math.LOmath.COmath.DS
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大Ramsey度与拓扑动力学

Big Ramsey degrees and topological dynamics

Andy Zucker

摘要:

我们考虑Fraïssé结构,其对象具有有限的大Ramsey度,并询问这对自同构群的动力学有什么影响。受D. Devlin关于有理数的划分性质,我们定义了大拉姆齐结构的概念,一个编码给定Fraïssé结构的大拉姆齐度的单一结构。这反过来又引出了完备流的定义;我们证明,如果Fraïssé结构允许大Ramsey结构,那么自同构群允许唯一的泛完备流。我们还讨论了大的拉姆齐结构何时存在的问题,并探讨了与Kechris,Pestov和Todorčević定义的振荡稳定性概念的联系

英文摘要:

We consider Fraïssé structures whose objects have finite big Ramsey degree and ask what consequences this has for the dynamics of the automorphism group. Motivated by a theorem of D. Devlin about the partition properties of the rationals, we define the notion of a big Ramsey structure, a single structure which codes the big Ramsey degrees of a given Fraïssé structure. This in turn leads to the definition of a completion flow; we show that if a Fraïssé structure admits a big Ramsey structure, then the automorphism group admits a unique universal completion flow. We also discuss the problem of when big Ramsey structures exist and explore connections to the notion of oscillation stability defined by Kechris, Pestov, and Todorčević

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