Robert Ralowski

  1. Completely nonmeasurable unions.

    Authors: Robert Ralowski, Szymon Zeberski
    Subjects: Logic
    Abstract

    Assume that there is no quasi-measurable cardinal smaller than $2^\omega$.
    ($\kappa$ is quasi measurable if there exists $\kappa $-additive ideal $\ci $
    of subsets of $\kappa $ such that the Boolean algebra $P(\kappa)/\ci$ satisfies
    c.c.c.) We show that for a c.c.c. $\sigma $-ideal I with a Borel base of
    subsets of an uncountable Polish space, if $\cal A$ is a point-finite family of
    subsets from I then there is an uncountable collection of pairwise disjoint
    subfamilies of $\cal A$ whose union is completely nonmeasurable i.e.

  2. Generalized Luzin sets.

    Authors: Robert Ralowski, Szymon Zeberski
    Subjects: Logic
    Abstract

    In this paper we invastigate the notion of generalized (I,J) - Luzin set.
    This notion generalize the standard notion of Luzin set and Sierpinski set. We
    find set theoretical conditions which imply the existence of generalized (I,J)
    - Luzin set. We show how to construct large family of pairwise non-equivalent
    (I,J) - Luzin sets. We find a class of forcings which preserves the property of
    being (I,J) - Luzin set.

  3. Remarks on nonmeasurable unions of big point families.

    Authors: Robert Ralowski
    Subjects: General Topology
    Abstract

    We show that under some conditions on a family $\mathcal{A}\subset\bbi$ there
    exists a subfamily $\mathcal{A}_0\subset\mathcal{A}$ such that $\bigcup
    \mathcal{A}_0$ is nonmeasurable with respect to a fixed ideal $\bbi$ with Borel
    base of a fixed uncountable Polish space. Our result applies to the classical
    ideal of null subsets of the real line and to the ideal of first category
    subsets of the real line.

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