Infinitely many small exotic Stein fillings
  We show that there exist infinitely many simply connected compact Stein 4-manifolds with b_2=2 such that they are all homeomorhic but mutually non-diffeomorphic, and they are Stein fillings of the same contact 3-manifold on their boundaries. We also describe their handlebody pictures. 
Selman Akbulut, Kouichi Yasui
math.GT math.SG