On bifurcations of area-preserving and non-orientable maps with   quadratic homoclinic tangencies
  We study bifurcations of non-orientable area-preserving maps with quadratic homoclinic tangencies. We study the case when the maps are given on non-orientable two-dimensional surfaces. We consider one and two parameter general unfoldings and establish results related to the emergence of elliptic periodic orbits. 
Amadeu Delshams, Marina Gonchenko and Sergey V. Gonchenko
math.DS