17,518 research outputs found
Independence in computable algebra
We give a sufficient condition for an algebraic structure to have a
computable presentation with a computable basis and a computable presentation
with no computable basis. We apply the condition to differentially closed, real
closed, and difference closed fields with the relevant notions of independence.
To cover these classes of structures we introduce a new technique of safe
extensions that was not necessary for the previously known results of this
kind. We will then apply our techniques to derive new corollaries on the number
of computable presentations of these structures. The condition also implies
classical and new results on vector spaces, algebraically closed fields,
torsion-free abelian groups and Archimedean ordered abelian groups.Comment: 24 page
Representing Scott sets in algebraic settings
We prove that for every Scott set there are -saturated real closed
fields and models of Presburger arithmetic
Finitely Generated Groups Are Universal
Universality has been an important concept in computable structure theory. A
class of structures is universal if, informally, for any
structure, of any kind, there is a structure in with the same
computability-theoretic properties as the given structure. Many classes such as
graphs, groups, and fields are known to be universal.
This paper is about the class of finitely generated groups. Because finitely
generated structures are relatively simple, the class of finitely generated
groups has no hope of being universal. We show that finitely generated groups
are as universal as possible, given that they are finitely generated: for every
finitely generated structure, there is a finitely generated group which has the
same computability-theoretic properties. The same is not true for finitely
generated fields. We apply the results of this investigation to quasi Scott
sentences
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