Erasmus Universiteit, Econometrisch Instituut, Postbus 1738, 3000~DR~~Rotterdam, The Netherlands
Abstract:
We provide an example of a zero-dimensional (separable metric) absolute Borel set which is not homogeneous, but whose square admits the structure of a topological group. We also construct a zero-dimensional absolute Borel set such that is a homogeneous non-group but is a group. This answers questions of Arhangel'skii and Zhou.