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Covering ω ω by special Cantor sets

Gary Gruenhage, Ronnie Levy (2002)

Commentationes Mathematicae Universitatis Carolinae

This paper deals with questions of how many compact subsets of certain kinds it takes to cover the space ω ω of irrationals, or certain of its subspaces. In particular, given f ω ( ω { 0 } ) , we consider compact sets of the form i ω B i , where | B i | = f ( i ) for all, or for infinitely many, i . We also consider “ n -splitting” compact sets, i.e., compact sets K such that for any f K and i ω , | { g ( i ) : g K , g i = f i } | = n .

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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