Some remarks on sign changing solutions of a quasilinear elliptic   equation in two variables
  We consider planar solutions to certain quasilinear elliptic equations subject to the Dirichlet boundary conditions; the boundary data is assumed to have finite number of relative maximum and minimum values. We are interested in certain vanishing properties of sign changing solutions to such a Dirichlet problem. Our method is applicable in the plane. 
Seppo Granlund and Niko Marola
math.AP