Dr Raphael Boll from the Technische Universität Berlin will give a talk on Thursday 21st November at 4pm in Carslaw 829 (AGR). All welcome! TITLE: Multi-time Lagrangian 1-forms for families of Bäcklund transformations. Relativistic Toda-type systems ABSTRACT: We establish the pluri-Lagrangian structure for families of Bäcklund transformations of relativistic Toda-type systems. This is a generalization of the results of our recent paper on non-relativistic Toda-type systems. However, we present an alternative approach to this theory using the pluri-Lagrangian structure of related two-dimensional variational equations which we discussed in another recent paper. Some but not all of them have their origin in the Lagrangian structure of quad-equations. Also in this situation, we have to deal with the multi-valuedness of the case of periodic boundary conditions and again we describe the branching behavior by usage of so-called superposition formulas. The proofs of the closure relation are a more or less direct consequence of the similar results of the related two-dimensional variational equations.