Christoph Hilmes: Ends of group pairs
Bass-Serre theory shows that a finitely generated group splits as a non-trivial amalgam or HNN-extension if and only if it acts on a tree without a global fixpoint. In the 90's, M. Sageev formulated a generalized Bass-Serre theory: A finitely generated group is semi-splittable if and only if it acts essentially on a CAT(0) cube complex. In this talk we'll explore the main ideas of the construction of the cubing and the associated action.
