<div class="csl-bib-body">
<div class="csl-entry">Müller, S., Schlicht, P., Schrittesser, D., & Weinert, T. V. (2022). Lebesgue’s density theorem and definable selectors for ideals. <i>Israel Journal of Mathematics</i>, <i>249</i>(2), 501–551. https://doi.org/10.1007/s11856-022-2312-8</div>
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dc.identifier.issn
0021-2172
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dc.identifier.uri
http://hdl.handle.net/20.500.12708/141937
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dc.description.abstract
We introduce a notion of density point and prove results analogous to Lebesgue’s density theorem for various well-known ideals on Cantor space and Baire space. In fact, we isolate a class of ideals for which our results hold. In contrast to these results, we show that there is no reasonably definable selector that chooses representatives for the equivalence relation on the Borel sets of having countable symmetric difference. In other words, there is no notion of density which makes the ideal of countable sets satisfy an analogue to the density theorem. The proofs of the positive results use only elementary combinatorics of trees, while the negative results rely on forcing arguments.
en
dc.description.sponsorship
Fonds zur Förderung der wissenschaftlichen Forschung (FWF)
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dc.language.iso
en
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dc.publisher
HEBREW UNIV MAGNES PRESS
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dc.relation.ispartof
Israel Journal of Mathematics
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dc.subject
Lebesgue's density
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dc.title
Lebesgue’s density theorem and definable selectors for ideals