English

Around definable types in $p$-adically closed fields

Logic 2024-07-18 v2

Abstract

We prove some technical results on definable types in pp-adically closed fields, with consequences for definable groups and definable topological spaces. First, the code of a definable nn-type (in the field sort) can be taken to be a real tuple (in the field sort) rather than an imaginary tuple (in the geometric sorts). Second, any definable type in the real or imaginary sorts is generated by a countable union of chains parameterized by the value group. Third, if XX is an interpretable set, then the space of global definable types on XX is strictly pro-interpretable, building off work of Cubides Kovacsics, Hils, and Ye. Fourth, global definable types can be lifted (in a non-canonical way) along interpretable surjections. Fifth, if GG is a definable group with definable f-generics (dfgdfg), and GG acts on a definable set XX, then the quotient space X/GX/G is definable, not just interpretable. This explains some phenomena observed by Pillay and Yao. Lastly, we show that interpretable topological spaces satisfy analogues of first-countability and curve selection. Using this, we show that all reasonable notions of definable compactness agree on interpretable topological spaces, and that definable compactness is definable in families.

Keywords

Cite

@article{arxiv.2208.05815,
  title  = {Around definable types in $p$-adically closed fields},
  author = {Pablo Andujar Guerrero and Will Johnson},
  journal= {arXiv preprint arXiv:2208.05815},
  year   = {2024}
}

Comments

39 pages; fixed two minor typos

R2 v1 2026-06-25T01:38:45.735Z