For pt.I see ibid., vol.6, p.1375 (1976). This new method is shown to give the exact result for U=0. It is implied that the same expansion in V kd will converge in both the large U, magnetic regime, and the small U, nonmagnetic regime.
No takes yet. Share an insight, caveat, or question.
S. E. Barnes (1977) studied this question.
Synapse has enriched 2 closely related papers on similar clinical questions. Consider them for comparative context: