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Construction techniques for some thin sets in duals of compact abelian groups

D. J. Hajela (1986)

Annales de l'institut Fourier

Various techniques are presented for constructing Λ (p) sets which are not Λ ( p + ϵ ) for all ϵ > 0 . The main result is that there is a Λ (4) set in the dual of any compact abelian group which is not Λ ( 4 + ϵ ) for all ϵ > 0 . Along the way to proving this, new constructions are given in dual groups in which constructions were already known of Λ (p) not Λ ( p + ϵ ) sets, for certain values of p . The main new constructions in specific dual groups are:– there is a Λ (2k) set which is not Λ ( 2 k + ϵ ) in Z ( 2 ) Z ( 2 ) for all 2 k , k N and ϵ > 0 , and in Z ( p ) Z ( p ) ( p a prime,...

Covering maps over solenoids which are not covering homomorphisms

Katsuya Eda, Vlasta Matijević (2013)

Fundamenta Mathematicae

Let Y be a connected group and let f: X → Y be a covering map with the total space X being connected. We consider the following question: Is it possible to define a topological group structure on X in such a way that f becomes a homomorphism of topological groups. This holds in some particular cases: if Y is a pathwise connected and locally pathwise connected group or if f is a finite-sheeted covering map over a compact connected group Y. However, using shape-theoretic techniques and Fox's notion...

Coverings and dimensions in infinite profinite groups

Peter Maga (2013)

Open Mathematics

Answering a question of Miklós Abért, we prove that an infinite profinite group cannot be the union of less than continuum many translates of a compact subset of box dimension less than 1. Furthermore, we show that it is consistent with the axioms of set theory that in any infinite profinite group there exists a compact subset of Hausdorff dimension 0 such that one can cover the group by less than continuum many translates of it.

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