How would the mathematics of electromagnetism and physical interpretation change if the Lorenz gauge used a difference instead of a sum?
In other words, what would this gauge do: $$\frac{1}{c}\frac{\partial \phi}{\partial t} - \nabla \cdot A=0$$ Instead of thisthe Lorenz gauge: $$\frac{1}{c}\frac{\partial \phi}{\partial t} + \nabla \cdot A=0$$