The embedding property for sorted profinite groups

TL;DR

This paper introduces the sorted embedding property (SEP) for sorted profinite groups, proves the existence of universal SEP-covers, and explores model-theoretic properties like $mbda$-stability, extending classical results in profinite group theory.

Contribution

It defines the SEP and FSEP, proves the existence and uniqueness of universal SEP-covers, and connects these to model-theoretic stability in sorted profinite groups.

Findings

Existence of universal SEP-covers for sorted profinite groups.

FSEP is equivalent to SEP and is first-order axiomatizable.

Sorted profinite groups with SEP are $mbda$-stable when the set of sorts is countable.

Abstract

We study the embedding property in the category of sorted profinite groups. We introduce a notion of the sorted embedding property (SEP), analogous to the embedding property for profinite groups. We show that any sorted profinite group has a universal SEP-cover. Our proof gives an alternative proof for the existence of a universal embedding cover of a profinite group. Also our proof works for any full subcategory of the sorted profinite groups, which is closed under taking finite quotients, fibre product, and inverse limit. We also introduce a weaker notion of finitely sorted embedding property (FSEP), and it turns out to be equivalent to SEP. The advantage of FSEP is to be able to be axiomatized in the first order language of sorted complete systems. Using this, we show that any sorted profinite group having SEP has the sorted complete system whose theory is $\omega$-stable under the assumption that the set of sorts is countable. In this case, as a byproduct, we get the uniqueness of a universal SEP-cover of a sorted profinite group, which generalizes the uniqueness of an embedding cover of a profinite group.