Existence without a singular diagonal product

In particular, a source-diagonal stress tensor does not produce a square of a propagator on identified endpoints in this tree. Two successive retarded kernels are composed through an independent intermediate variable.

The output is not a linear test class in $\mathcal{D}/P_m\mathcal{D}$. It is a cubic classical polynomial symbol. A quantum admission into ${\mathcal{A}}_0$ is a separate step not supplied by Theorem thm:tree.