## Real Analysis Exchange

### Constructing Δ30 using topologically restrictive countable disjoint unions.

Abhijit Dasgupta

#### Abstract

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 $\mathcal{G}_{\delta\sigma}$.

#### Article information

Source
Real Anal. Exchange, Volume 31, Number 2 (2005), 547-551.

Dates
First available in Project Euclid: 10 July 2007

Permanent link to this document
https://projecteuclid.org/euclid.rae/1184104046

Mathematical Reviews number (MathSciNet)
MR2265795

#### Citation

Dasgupta, Abhijit. Constructing Δ 3 0 using topologically restrictive countable disjoint unions. Real Anal. Exchange 31 (2005), no. 2, 547--551. https://projecteuclid.org/euclid.rae/1184104046

#### References

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