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Transactions of the American Mathematical Society

ISSN 1088-6850(online) ISSN 0002-9947(print)



One-dimensional asymptotic classes of finite structures

Authors: Dugald Macpherson and Charles Steinhorn
Journal: Trans. Amer. Math. Soc. 360 (2008), 411-448
MSC (2000): Primary 03C45; Secondary 03C13
Published electronically: August 14, 2007
MathSciNet review: 2342010
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Abstract: A collection $ {\mathcal C}$ of finite $ \mathcal{L}$-structures is a 1-dimensional asymptotic class if for every $ m \in {\mathbb{N}}$ and every formula $ \varphi(x,\bar{y})$, where $ \bar{y}=(y_1,\ldots,y_m)$:

There is a positive constant $ C$ and a finite set $ E\subset {\mathbb{R}}^{>0}$ such that for every $ M\in {\mathcal C}$ and $ \bar{a}\in M^m$, either $ \vert\varphi(M,\bar{a})\vert\leq C$, or for some $ \mu\in E$,

$\displaystyle \big\vert\vert\varphi(M,\bar{a})\vert-\mu \vert M\vert\big\vert \leq C\vert M\vert^{\frac{1}{2}}.$

For every $ \mu\in E$, there is an $ \mathcal{L}$-formula $ \varphi_{\mu}(\bar{y})$, such that $ \varphi_{\mu}(M^m)$ is precisely the set of $ \bar{a}\in M^m$ with

$\displaystyle \big\vert\vert\varphi(M,\bar{a})\vert-\mu \vert M\vert\big\vert \leq C\vert M\vert^{\frac{1}{2}}.$

One-dimensional asymptotic classes are introduced and studied here. These classes come equipped with a notion of dimension that is intended to provide for the study of classes of finite structures a concept that is central in the development of model theory for infinite structures. Connections with the model theory of infinite structures are also drawn.

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Additional Information

Dugald Macpherson
Affiliation: Department of Pure Mathematics, University of Leeds, Leeds LS2 9JT, England

Charles Steinhorn
Affiliation: Department of Mathematics, Vassar College, 124 Raymond Avenue, Poughkeepsie, New York 12604

Received by editor(s): February 24, 2006
Published electronically: August 14, 2007
Additional Notes: This work was partially supported by NSF grants DMS-9704869 and DMS-0070743, EPSRC grant GR/R37388/01, and the London Mathematical Society.
Article copyright: © Copyright 2007 American Mathematical Society

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