Divergence form elliptic equations with discontinuous coefficients

In this paper we derive global W-1,W- infinity and piecewise C-1,C- alpha estimates for solutions to divergence form elliptic equations with piecewise Holder continuous coefficients. The novelty of these estimates is that, even though they depend on the shape and on the size of the surfaces of discontinuity of the coefficients, they are independent of the distance between these surfaces.