Scaling is applied to numerical building blocks

For $u^{\circ }\in {\mathcal{D}}^{\prime }({\mathbb{R}}^4\setminus \{0\})$, use the usual scaling degree at the origin:

with the normalized rescaling of tests.

The diagonal $y=w$ has codimension four. Use coordinates $(r,w)=(y-w,w)$; $w$ is tangential. The smooth interaction and preparation coefficients are not part of the translation-invariant numerical kernel.