On the tangential touch between the free and the fixed boundaries for   the two-phase obstacle-like problem
  In this paper we consider the following two-phase obstacle-problem-like equation in the unit half-ball $\Delta u = \lambda_{+}\chi_{\{u>0\}}-\lambda_{-}\chi_{\{u<0\}}, \lambda_\pm>0$. We prove that the free boundary touches the fixed one in (uniformly) tangential fashion if the boundary data $f$ and its first and second derivatives vanish at the touch-point. 
John Andersson, Norayr Matevosyan, Hayk Mikayelyan