XII-F: the retained pairing and witness

For the kernel calculation only, we also use XII-F's admission of the auxiliary row: for fixed $\xi ,f,g$ its bilinear kernel in $(b,\varphi )$ is compact and has wavefront set contained in $Z_2$. This is the kernel used in its nonzero-class proof, not the cubic kernel of ${\mathcal{C}}_{3,\mathrm{D}}$.