An example of a map which is $C^2$ robustly transitive but not $C^1$   (robustly transitive)
  The aim of this work is to exhibit an example of an endomorphism of $\T^{2}$ which is $C^2$-robustly transitive but not $C^1$-robustly transitive. 
Jorge Iglesia, Aldo Portela
math.DS