Evolutionary constraints: Gluing in a toy model

It is possible to solve the Einstein constraint equations as an evolutionary rather than an elliptic system. Here we consider the Gauss constraint in electrodynamics as a toy model for thist. We use a combination of the evolutionary method with the gluing construction to produce initial data for an electromagnetic pulse surrounded by vacuum. It turns out that solving the evolutionary form of the constraint is straightforward, and explicitly yields the desired type of initial data. In contrast, proving the existence of a solution to the same problem within the elliptic setting requires sophisticated arguments based on functional analysis.