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arXiv 0706.0182math.LO
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实封闭的域的O-极小展开上的标准部分映射在实域上的结构

The structure on the real field generated by the standard part map on an o-minimal expansion of a real closed field

Jana Maříková

摘要:

设R是实封闭的域的充分饱和o-极小展开式,O是R中有理数的凸包,st:O^\to \mathbb{R}^n是标准部分映射.对于X \subseteq R^n,定义st(X):=st(X \cap O^n)。我们让\mathbb{R}_{\ind}是具有底层集合\mathbb{R}的结构,并由所有形式为st(X)的集合展开,其中X \subseteq R^{n}在R中可定义,并且n= 1,2,.我们证明了在\mathbb{R}_{\ind}中可定义的\mathbb{R}^n的子集恰好是st(X)\setminus st(Y)形式的集合的有限并,其中X,Y \subseteq R^n在R中可定义。该证明的结果是对Hrushovski、Peterzil和Pillay提出的关于R^n中有界可定义集的格上存在具有某些不变性性质的测度的问题的部分回答。

英文摘要:

Let R be a sufficiently saturated o-minimal expansion of a real closed field, let O be the convex hull of the rationals in R, and let st: O^n \to \mathbb{R}^n be the standard part map. For X \subseteq R^n define st(X):=st(X \cap O^n). We let \mathbb{R}_{\ind} be the structure with underlying set \mathbb{R} and expanded by all sets of the form st(X), where X \subseteq R^{n} is definable in R and n=1,2,.... We show that the subsets of \mathbb{R}^n that are definable in \mathbb{R}_{\ind} are exactly the finite unions of sets of the form st(X) \setminus st(Y), where X,Y \subseteq R^n are definable in R. A consequence of the proof is a partial answer to a question by Hrushovski, Peterzil and Pillay about the existence of measures with certain invariance properties on the lattice of bounded definable sets in R^n.

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