The joint product obstruction remains a separate statement

For the frozen data and F1 hypotheses of Cheung's XI-G thm:obstruction, the supplied result is

Here $[u{]}_{\mathrm{sol}}$ is the class of compact cubic kernels with two metric slots and one scalar slot, identified by equality on the declared free solutions; ${\mathcal{F}}_{\mathrm{mc},\mathrm{pol}}$ is the predecessor's admissible microcausal polynomial target CheungXIG. We neither enlarge that target nor change the frozen class.