The purpose of this paper is to present an overview of the Edge-Ray Theorem in 2D geometry, covering the different optical systems treated up today, including some cases (as the refraction/reflection of sequential optical surfaces) which have not been formally discussed previously, and also analyzing the role of slope discontinuities in the creation/annihilation on edge rays.
Also illustrative novel examples are given. In section 2, a simple device that seems to beat either the Edge Ray Theorem or the Second Law of Thermodynamics is presented. In section 6, it is proven that there exits perfect solution to the theoretical problem of achieving maximum concentration on a circular receiver from a source at infinity with a single slope discontinuity and a sizeable gap between optics and receiver. At the end (section 7), the explanation of the device of section 2 offending the Edge Ray Theorem will be given.