Conditional source contacts, subtraction, and order audit

The statement excludes only those simultaneous assumptions. An independent central source need not be identified with $P_{\mathrm{f}}h$. A free bisolution equation $P_{\mathrm{f}}H=0$ is a different input. The two-slot contact is not the three-observation residue $r$, and cannot be absorbed merely by changing $c$ IXD ({:contact}).