We propose a metasurface that generalizes classical Snell and Fresnel laws, based on phase discontinuities. I provide an outlook on this structure, from different and complementary points of view, referred to classical Huygens, Fermat, Bragg, Friedel and Fresnel laws. The structure shows a generalization of the concept of crystallographic systematic absence. As a result, the Friedel law of crystals completely breaks down. A novel concept of "metacrystal" can be introduced, where systematic absences can be originated from form factors of meta-atoms, in contrast with natural absences, which are based on structure factors only. Applications will be also presented.