We investigate what Ext(A, Z) can be when A is torsion-free and Hom(A, Z) = 0. We thereby give an answer to a question of Golasiński and Gonçalves which asks for the divisible Abelian groups which can be the type of a co-Moore space. 0. Introduction Marek Golasiński and Daciberg Lima Gonçalves have asked which divisible abelian groupsD can be the type of a co-Moore space [6, Problem 2.6]. In ot...

We study the algorithmic content of Pontryagin - van Kampen duality. prove that process dualization is computable in important cases compact and locally totally disconnected Polish abelian groups. The applications our main results include solutions to questions Kihara Ng about presentations connected spaces, an unexpected arithmetical characterisation direct products solenoid groups among all

This short research announcement briefly describes the simplicial method underlying the GAP package SCO for computing the socalled orbifold cohomology of topological resp. smooth orbifolds. SCO can be used to compute the lower dimensional group cohomology of some infinite groups. Instead of giving a complete formal definition of an orbifold, we start with a simple construction, general enough t...

We determine several necessary and sufficient conditions for a closed almost-complex orbifold Q with abelian local groups to admit a nonvanishing vector field. These conditions are stated separately in terms of the orbifold Euler-Satake characteristics of Q and the connected components of its twisted sectors, the Euler characteristics of the underlying topological spaces of Q and the components...