Construction of an Uncountable Difference between ${\mit\Phi}(B)$ and ${\mit\Phi}_f(B)$
Volume 56 / 2008
Bulletin Polish Acad. Sci. Math. 56 (2008), 121-130
MSC: Primary 28A05, 26A03.
DOI: 10.4064/ba56-2-4
Abstract
We construct a set $B$ and homeomorphism $f$ where $f$ and $f^{-1}$ have property N such that the symmetric difference between the sets of density points and of $f$-density points of $B$ is uncountable.
