1. E.A. Uehling, Phys. Rev. 48, 55 (1935)
2. A. Akhiezer, V.B. Berestetskii, Quantum Electrodynamics (4th ed., Science, Moscow (1981)) [in Russian]
3. V.B. Berestetskii, E.M. Lifshitz, L.P. Pitaevskii, Relativistic Quantum Theory (Pergamon Press, Oxford, 1971)
4. W. Greiner, J. Reinhardt, Quantum Electrodynamics, 4th ed. (Springer Verlag, Berlin, 2009)
5. T. Dubler, K. Kaeser, B. Robert-Tissot, L.A. Schaller, L. Schellenberg, H. Schneuwly, Nucl. Phys. A 294, 397 (1978)