The revised Newelski conjecture on Hausdorffness of the tau-topology

From papers

Let MM be a model of an NIP theory, let GG be a 00-definable group in MM, and let NMN\succ M be an M+|M|^{+}-saturated elementary extension. Let SGfs(N,M)S_G^{\operatorname{fs}}(N,M) be the semigroup of complete types over NN concentrated on GG and finitely satisfiable in MM. Let M\mathcal{M} be a minimal left ideal of this semigroup, and let uMu\in\mathcal{M} be an idempotent. Revised Newelski conjecture. The τ\tau-topology on uMu\mathcal{M} is Hausdorff. This conjecture is the revised form of Newelski's Ellis group conjecture and predicts Hausdorffness of the ideal group in the NIP setting; the paper proves it for countable NIP groups, while the general case remains open.

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Primary source

Artem Chernikov, Kyle Gannon and Krzysztof Krupiński, “Definable convolution and idempotent Keisler measures III. Generic stability, generic transitivity, and revised Newelski's conjecture”, arXiv:2406.00912 (2025).

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