Computable dyadic subbases and $\mathbf{T}^\omega$-representations of compact sets

Abstract

We explore representing the compact subsets of a given represented space by infinite sequences over Plotkin's $\mathbb{T}$. We show that computably compact computable metric spaces admit representations of their compact subsets in such a way that compact sets are essentially underspecified points. We can even ensure that a name of an $n$-element compact set contains $n$ occurrences of $\bot$. We undergo this study effectively and show that such a $\mathbb{T}^\omega$-representation is effectively obtained from structures of computably compact computable metric spaces. As an application, we prove some statements about the Weihrauch degree of closed choice for finite subsets of computably compact computable metric spaces. Along the way, we introduce the notion of a computable dyadic subbase, and prove that every computably compact computable metric space admits a proper computable dyadic subbase.