n](x)} is a regular sequence of infinitely differentiable functions converging to the Dirac delta-function
This arrangement is in agreement with the fact that we can integrate a delta-function (charge) but we cannot integrate its square (would be energy).
However, there are no provisions on the surface current density (if a surface current is different from zero then its density is necessarily expressed by a delta-function across the disruption surface).
If the acceleration of the source is a delta-function
peaked at t = t, r = 0, then the advanced field of the source vanishes everywhere at t; we need to look closely, however, to see if X does as well.
The analyzed the very classical problem of signal processing how the wide spectrum of the single pulse approaches the delta-function like spectrum of the periodic signal.
1] by using a separated delta-function forming multiplier.