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JOURNALS // Matematicheskie Trudy // Archive

Mat. Tr., 2005 Volume 8, Number 2, Pages 3–38 (Mi mt60)

This article is cited in 4 papers

Definability of 1-Types in Weakly $o$-Minimal Theories

B. S. Baizhanov

Institute for Problems of Informatics and Control Sciences

Abstract: In the article, we prove a criterion for definability of 1-types over sets in weakly $o$-minimal theories in terms of left and right convergences of a formula to a type.
Van den Dries proved that every type over the field of reals is definable. Marker and Steinhorn strengthened his result. They (and, later, Pillay) proved the following assertion. Let $M\prec N$ be a pair of models of some $o$-minimal theory. If, for each element of $N$, the type of this element over $M$ is definable then, for each tuple of elements of $N$, the type of this tuple over $M$ is definable.
We construct a weakly $o$-minimal theory for which the Marker–Steinhorn theorem fails; i. e., some pair of models of the theory possesses the following property: For all elements of the larger model, the 1-type over the smaller model is definable but there exists a tuple of elements of the larger model whose 2-type over the smaller model is not definable.

Key words: definable type, weakly $o$-minimal theory, nonorthogonality of types.

UDC: 510.67

Received: 19.02.2004


 English version:
Siberian Advances in Mathematics, 2006, 16:2, 1–33

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