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On c-sets and products of ideals

Marek Balcerzak — 1991

Colloquium Mathematicae

Let X, Y be uncountable Polish spaces and let μ be a complete σ-finite Borel measure on X. Denote by K and L the families of all meager subsets of X and of all subsets of Y with μ measure zero, respectively. It is shown that the product of the ideals K and L restricted to C-sets of Selivanovskiĭ is σ-saturated, which extends Gavalec's results.

Generalized projections of Borel and analytic sets

Marek Balcerzak — 1996

Colloquium Mathematicae

For a σ-ideal I of sets in a Polish space X and for A ⊆ X 2 , we consider the generalized projection (A) of A given by (A) = x ∈ X: Ax ∉ I, where A x =y ∈ X: 〈x,y〉∈ A. We study the behaviour of with respect to Borel and analytic sets in the case when I is a 2 0 -supported σ-ideal. In particular, we give an alternative proof of the recent result of Kechris showing that [ 1 1 ( X 2 ) ] = 1 1 ( X ) for a wide class of 2 0 -supported σ-ideals.

Convergence theorems for the Birkhoff integral

Marek BalcerzakMonika Potyrała — 2008

Czechoslovak Mathematical Journal

We give sufficient conditions for the interchange of the operations of limit and the Birkhoff integral for a sequence ( f n ) of functions from a measure space to a Banach space. In one result the equi-integrability of f n ’s is involved and we assume f n f almost everywhere. The other result resembles the Lebesgue dominated convergence theorem where the almost uniform convergence of ( f n ) to f is assumed.

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