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On nonmeasurable unions |
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| Authors: | Jacek Cichoń Robert Ra?owski |
| Institution: | a Institute of Mathematics and Computer Science, Wroc?aw University of Technology, Wybrze?e Wyspiańskiego 27, 50-370 Wroc?aw, Poland b Institute of Mathematics, University of Wroc?aw, pl. Grunwaldzki 2/4, 50-384 Wroc?aw, Poland |
| Abstract: | For a Polish space X and a σ-ideal I of subsets of X which has a Borel base we consider families A of sets in I with the union ?A not in I. We determine several conditions on A which imply the existence of a subfamily A′ of A whose union ?A′ is not in the σ-field generated by the Borel sets on X and I. Main examples are X=R and I being the ideal of sets of Lebesgue measure zero or the ideal of sets of the first Baire category. |
| Keywords: | primary 03E35 03E75 secondary 28A99 |
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