  We introduce a paradigm for accurate design of metasurfaces for intricate
beam manipulation, implementing functionalities previously considered
impossible to achieve with passive lossless elements. The key concept involves
self-generation of auxiliary evanescent fields which facilitate the required
local power conservation, without interfering with the device performance in
the far field. We demonstrate our scheme by presenting exact reactive solutions
to the challenging problems of reflectionless beam splitting and perfect
reflection, verified via full wave simulations.
