Finite orbits for nilpotent actions on the torus
  A homeomorphism of the $2$-torus with Lefschetz number different from zero has a fixed point. We give a version of this result for nilpotent groups of diffeomorphisms. We prove that a nilpotent group of $2$-torus diffeomorphims has finite orbits when the group has some element with Lefschetz number different from zero. 
Sebasti\~ao Firmo and Javier Rib\'on
math.DS