Approximate Green's Function for the Conductivity Equation With Conormal   Coefficient
  We construct an approximate Green's function for $L_{\gamma}=\nabla \cdot \gamma(x) \nabla u(x)$, which belongs to a class of Fourier Integral Operators (FIOs) associated to two canonical relations. This leads to analysis of the composition of two FIOs, associated to a canonical relation with a zero section problem. The resulting composition is a sum of two FIOs, each associated to two intersecting canonical relations. 
Denitza Ivanova Straub
math.AP