F. Vanengelen, A NONHOMOGENEOUS ZERO-DIMENSIONAL X SUCH THAT X-X-X IS A GROUP, Proceedings of the American Mathematical Society, 124(8), 1996, pp. 2589-2598
We provide an example of a zero-dimensional (separable metric) absolut
e Borel set X which is not homogeneous, but whose square X x X admits
the structure of a topological group. We also construct a zero-dimensi
onal absolute Borel set Y such that Y is a homogeneous non-group but Y
x Y is a group. This answers questions of Arhangel'skii and Zhou.