Noiselessness of the open core without definable integers

Let R{\mathscr{R}} be an expansion of (R,<,+,×)(\mathbb{R},<,+,\times), and let R{\mathscr{R}}^\circ be its open core. The structure R{\mathscr{R}} is type A when it has no dense definable subset of an interval admitting a definable ordering of order type ω\omega. Noiselessness conjecture. If R{\mathscr{R}} is type A, then R{\mathscr{R}}^\circ is noiseless. In particular, if R{\mathscr{R}} expands (R,<,+,×)(\mathbb{R},<,+,\times) and does not define Z\mathbb{Z}, then R{\mathscr{R}}^\circ is noiseless. This is presented as the main conjecture for expansions of the real ordered additive group; its relation to dense ω\omega-orders and definability of the integers motivates the claim.

Sources & referencesView supporting material

Primary source

Erik Walsberg, “Externally definable quotients and NIP expansions of the real ordered additive group”, arXiv:1910.10572 (2020).

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