The structure of the sigma-ideal of sigma-porous sets

Abstrakt

A general method of construction of non-sigma-porous sets in complete metric spaces is presented. It is proved that each non-sigma-porous Suslin subset of a topologically complete metric space contains a non-sigma-porous closed subset.

We show also a sufficient condition, which gives that a certain system of compact sets contains a non-sigma-porous element. Several applications of this result to problems from real and harmonic analysis is showed.