Submission date: 28 December 2020

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 ω-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.

Mathematics Subject Classification: 03C60, 03C45, 20E18

Keywords and phrases: sorted profinite groups, sorted embedding property, universal sorted embedding cover

Full text arXiv 2012.14149: pdf, ps.