Ill-posedness of the incompressible Euler equations in the $C^1$ space
  We prove that the 2D Euler equations are not locally well-posed in $C^1$. Our approach relies on the technique of Lagrangian deformations and norm inflation of Bourgain and Li. We show that the assumption that the data-to-solution map is continuous in $C^1$ leads to a contradiction with a well-posedness result in $W^{1,p}$ of Kato and Ponce. 
Gerard Misio{\l}ek and Tsuyoshi Yoneda
math.AP