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2005/2006 Constructing Δ30 using topologically restrictive countable disjoint unions.
Abhijit Dasgupta
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Real Anal. Exchange 31(2): 547-551 (2005/2006).


In a zero-dimensional Polish space, the Borel sets are generated from the clopen sets by repeatedly applying the operations of countable disjoint union and complementation. Here we look at topologically restrictive versions of the general countable disjoint union of sets, and obtain ``construction principles'' for $\mathbf{\Delta} \begin{smallmatrix} 0 \\ 3 \end{smallmatrix}$, i.e., sets which are both $\mathcal{F}_{\sigma\delta}$ and $\mathcal{G}_{\delta\sigma}$.


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Abhijit Dasgupta. "Constructing Δ30 using topologically restrictive countable disjoint unions.." Real Anal. Exchange 31 (2) 547 - 551, 2005/2006.


Published: 2005/2006
First available in Project Euclid: 10 July 2007

MathSciNet: MR2265795

Primary: 03E15 , 28A05 , 54H05

Keywords: $\boldsymbol{\Delta}^{\boldsymbol{0}}_{\boldsymbol{3}}$ , Borel sets , Polish space , separated union

Rights: Copyright © 2005 Michigan State University Press

Vol.31 • No. 2 • 2005/2006
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