https://www.scirp.org/reference/referencespapers?referenceid=1252067
Berestetskii, V.B., Lifshitz, E.M. and Pithaevskii, L.P. (1971) Relativistic Quantum Theory....
Berestetskii, V.B., Lifshitz, E.M. and Pithaevskii, L.P. (1971) Relativistic Quantum Theory. Pergamon Press, Oxford.