Around definable types in $p$-adically closed fields

Abstract

We prove some technical results on definable types in $p$-adically closed fields, with consequences for definable groups and definable topological spaces. First, the code of a definable $n$-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 $X$ is an interpretable set, then the space of global definable types on $X$ 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 $G$ is a definable group with definable f-generics ($dfg$), and $G$ acts on a definable set $X$, then the quotient space $X/G$ 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.

arXiv comment39 pages; fixed two minor typos

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