On extremal and perfect σ-algebras for $ℤ^{d}$-actions on a Lebesgue space
Tom 124 / 1997
Studia Mathematica 124 (1997), 173-178
DOI: 10.4064/sm-124-2-173-178
Streszczenie
We show that for every positive integer d there exists a $ℤ^d$-action and an extremal σ-algebra of it which is not perfect.
