On unions of porous sets. (English) Zbl 0879.28002

Porous sets form a hereditary class of subsets of the real line contained in the class of nowhere dense Lebesgue null sets. The paper gives several examples showing that porous sets are not stable under finite unions.


28A05 Classes of sets (Borel fields, \(\sigma\)-rings, etc.), measurable sets, Suslin sets, analytic sets
26A03 Foundations: limits and generalizations, elementary topology of the line
26A21 Classification of real functions; Baire classification of sets and functions
03E15 Descriptive set theory