A third consequence of the mathematical consistency is that each of the world scalar S ~ ~ i and four vector A ~ ~ i μ μ potentials has a term with a fixed dependence on γ γ 1 and γ γ 2 in addition to the gamma matrix independent forms of S i and A i μ μ which appear in the ordinary one-body Dirac equation for scalar and vector potentials. These extra terms correspond to additional recoil spin-dependence not present in the one-body Dirac equation and vanish when one of the particles becomes very heavy (the so-called static limit).