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Preprint Number 1361

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1361. Daniel Palacín and Saharon Shelah
On the class of flat stable theories

Submission date: 4 January 2018


A new notion of independence relation is given and associated to it, the class of flat theories, a subclass of strong stable theories including the superstable ones is introduced. More precisely, after introducing this independence relation, flat theories are defined as an appropriate version of superstability. It is shown that in a flat theory every type has finite weight and therefore flat theories are strong. Furthermore, it is shown that under reasonable conditions any type is non-orthogonal to a regular one. Concerning groups in flat theories, it is shown that type-definable groups behave like superstable ones, since they satisfy the same chain condition on definable subgroups and also admit a normal series of definable subgroups with semi-regular quotients.

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Full text arXiv 1801.01438: pdf, ps.

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