The ideal generated by σ-nowhere dense sets
نویسندگان
چکیده
منابع مشابه
The σ-ideal generated by H-sets∗
It is consistent with the axioms of set theory that the circle T can be covered by א1 many closed sets of uniqueness while a much larger number of H-sets is necessary to cover it. In the proof of this theorem, the descriptive set theoretic phenomenon of overspill appears, and it is reformulated as a natural forcing preservation principle that persists through the operation of countable support ...
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We prove that there is a Gδ σ-ideal of compact sets which is strictly above NWD in the Tukey order. Here NWD is the collection of all compact nowhere dense subsets of the Cantor set. This answers a question of Louveau and Veličković asked in [4].
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We prove that there is a Gδ σ-ideal of compact sets which is strictly above NWD in the Tukey order. Here NWD is the collection of all compact nowhere dense subsets of the Cantor set. This answers a question of Louveau and Veličković asked in [4].
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We investigate Tukey functions from the ideal of all closed nowhere dense subsets of 2N. In particular, we answer an old question of Isbell and Fremlin by showing that this ideal is not Tukey reducible to the ideal of density zero subsets of N. We also prove non-existence of various special types of Tukey reductions from the nowhere dense ideal to analytic P-ideals. In connection with these res...
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We recall from [10] a Gδ σ-ideal of compact subsets of 2 ω and prove that it is not Tukey reducible to the ideal I1/n = {H ⊆ ω : ∑ h∈H 1/h <∞}. This result answers a question of S. Solecki and S. Todorčević in the negative.
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ژورنال
عنوان ژورنال: Applied General Topology
سال: 2006
ISSN: 1989-4147,1576-9402
DOI: 10.4995/agt.2006.1928