Completely nonmeasurable unions

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 $P(κ)/\ci$ 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 $\mathcal{A}$ is a point-finite family of subsets from I then there is an uncountable collection of pairwise disjoint subfamilies of $\mathcal{A}$ whose union is completely nonmeasurable i.e. its intersection with every non-small Borel set does not belong to the $\sigma$-field generated by Borel sets and the ideal I. This result is a generalization of Four Poles Theorem.

6 pages