We prove that the isomorphism and quasi-isomorphism relations on the p-local torsion-free abelian groups of fixed finite rank n are incomparable with respect to Borel reducibility.
We investigate the structures of crossed products of the Cuntz algebra O∞ by quasi-free actions of abelian groups. We completely determine their ideal structures and compute the strong Connes spectra and K-groups.
Let $A$ be an abelian topological group and $B$ a trivial topological $A$-module. In this paper we define the second bilinear cohomology with a trivial coefficient. We show that every abelian group can be embedded in a central extension of abelian groups with bilinear cocycle. Also we show that in the category of locally compact abelian groups a central extension with a continuous section can b...
