Normal Form for Edge Metrics
  A normal form for edge metrics is derived under the necessary conditions that the metric be normalized and exact. The normal forms for such an edge metric are shown to be in 1-1 correspondence with representative metrics for a reduced conformal infinity on the boundary. The normal form is constructed via solution of a singular eikonal equation at infinity. The eikonal equation is solved by proving existence and uniqueness of smooth solutions of a class of characteristic nonlinear first-order initial value problems. This is carried out by constructing a characteristic version of a Hamiltonian flow-out in the first jet bundle of the solution. 
C. Robin Graham and Joshua M. Kantor
math.AP math.DG