The benignity conjecture for subsets of models of stable theories

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Let TT be a stable theory, let MM be a model of TT, and let A⊆MA\subseteq M. The set AA is benign in MM if equality of types over AA implies equality of the corresponding types in the language expanded by a predicate for AA. The benignity conjecture. Every subset A⊆MA\subseteq M is benign. Shelah observed a counterexample: there is an ω\omega-stable rank-22 theory with ndop having a model and a subset that is not benign. Thus the conjecture is refuted.

References

Primary source

Bektur Baizhanov, John Baldwin and Saharon Shelah, “Subsets of superstable structures are weakly benign”, arXiv:math/0303324 (2003).

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