English

Small sets in dense pairs

Logic 2018-12-21 v4

Abstract

Let M~=M,P\widetilde{\mathcal M}=\langle \mathcal M, P\rangle be an expansion of an o-minimal structure M\mathcal M by a dense set PMP\subseteq M, such that three tameness conditions hold. We prove that the induced structure on PP by M\mathcal M eliminates imaginaries. As a corollary, we obtain that every small set XX definable in M~\widetilde{\mathcal M} can be definably embedded into some PlP^l, uniformly in parameters, settling a question from [10]. We verify the tameness conditions in three examples: dense pairs of real closed fields, expansions of M\mathcal M by a dense independent set, and expansions by a dense divisible multiplicative group with the Mann property. Along the way, we point out a gap in the proof of a relevant elimination of imaginaries result in Wencel [17]. The above results are in contrast to recent literature, as it is known in general that M~\widetilde{\mathcal M} does not eliminate imaginaries, and neither it nor the induced structure on PP admits definable Skolem functions.

Cite

@article{arxiv.1704.05802,
  title  = {Small sets in dense pairs},
  author = {Pantelis E. Eleftheriou},
  journal= {arXiv preprint arXiv:1704.05802},
  year   = {2018}
}
R2 v1 2026-06-22T19:21:40.055Z