Newelski's Ellis group conjecture for definable flows

Let MM be a first-order structure and let GG be an MM-definable group. The space Sext,G(M)S_{ext,G}(M) is the universal definable flow of GG over MM, and G00G^{00} is the smallest type-definable subgroup of GG of bounded index. Under relatively tame assumptions, generally understood to include NIPNIP, Newelski's Ellis group conjecture. The Ellis group of Sext,G(M)S_{ext,G}(M) is isomorphic to

G/G00.G/G^{00}.

The source identifies this as Newelski's conjecture and separately records positive results in several tame settings, while the broader conjecture has counterexamples. This environment is a restatement of the earlier prose formulation and is therefore merged into the same database row.

Sources & referencesView supporting material

Primary source

Grzegorz Jagiella, “The Ellis group conjecture and variants of definable amenability”, arXiv:1710.11081 (2017).

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