Torsors for Difference Algebraic Groups
  We introduce a cohomology set for groups defined by algebraic difference equations and show that it classifies torsors under the group action. This allows us to compute all torsors for large classes of groups. We also develop some tools for difference algebraic geometry and present an application to the Galois theory of differential equations depending on a discrete parameter. 
Annette Bachmayr, Michael Wibmer
math.AG math.AC math.RA