On the characteristic initial value problem for nonlinear symmetric   hyperbolic systems, including Einstein equations
  We consider a characteristic initial value problem for a class of symmetric hyperbolic systems with initial data given on two smooth null intersecting characteristic surfaces. We prove existence of solutions on a future neighborhood of the initial surfaces. The general result is applied to general semilinear wave equations, as well as the Einstein equations with or without sources, and conformal variations thereof. 
Aurore Cabet, Piotr T. Chru\'sciel, Roger Tagne Wafo
gr-qc math.AP