Edge-of-the-wedge theorem

In mathematics, the edge-of-the-wedge theorem implies that holomorphic functions on two "wedges" with an "edge" in common are analytic continuations of each other provided they both give the same continuous function on the edge. It is used in quantum field theory to construct the analytic continuation of Wightman functions.

Source: Wikipedia — Edge-of-the-wedge theorem (CC BY-SA 4.0)