Kernel representation of the first coefficient

The onset $\theta (y^0)$ is the sharp step $\theta (t)$ that X-A replaced by ${\sigma }_{\epsilon }$ in the coordinate operator (X-A, kernel lemma), and that VII-B found to carry a timelike conormal covector. Here it reappears in a metric slot, where the ramp does not act. Whether it is harmless depends on whether the coefficient $\beta$ vanishes on $\Sigma$. It does not.