  The non-invariant energy functional of the preceding paper is improved in
order to obtain its gauge-invariant form by strictly taking into account the
non-Abelian character of Relativistic Schroedinger Theory (RST). As an
application of the results, the dichotomy of positronium with respect to
singlet and triplet states is discussed (ortho- and para-positronium). The
degeneracy of the ortho- and para-states occurs in RST if (i) the magnetic
interactions are neglected (as in the conventional theory) and (ii) the
anisotropy of the electric interaction potential is disregarded. In view of
such a very crude approximation procedure, the non-relativistic positronium
spectrum in RST agrees amazingly well with the conventional predictions.
