فهرست نشریات علمی دسترسی آزاد ایران

The paper begins with a brief history of this topologist's interactions with Derek J. S. Robinson. It continues with a topological proof of Derek's result showing that the Schur multiplier of a generalized Baumslag-Solitar group $G$ is free abelian of rank one less than the rank of the torsion free first homology of $G$ and that both of these ranks can be computed by inspecting a weighted directed graph associate to $G$. In this paper the topology of a special subclass of Seifert fibred 2-dimensional complexes is used to provide proofs of Derek's results.