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Preprint Number 1625

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1625. M. Malliaris, S. Shelah
Keisler's order is not simple (and simple theories may not be either)

Submission date: 24 June 2019


Solving a decades-old problem we show that Keisler's 1967 order on theories has the maximum number of classes. The theories we build are simple unstable with no nontrivial forking, and reflect growth rates of sequences which may be thought of as densities of certain regular pairs, in the sense of Szemerédi's regularity lemma. The proof involves ideas from model theory, set theory, and finite combinatorics.

Mathematics Subject Classification:

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Full text arXiv 1906.10241: pdf, ps.

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