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In the partial case of a constant electromagnetic field, generated by magnetic charges, when for A$_{µ}$ expression (29): 

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– may be used, the chronological coupling of operators A$_{µ}$ and B$_{µ}$ is equal 

<img src='content_image/340997.jpg'>

Similarly, for a constant electromagnetic field, generated by electrical charges, 

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[2] P. A. M. Dirac, Scientific American, 208, No. 5, 45 (1963). 

[3] K. A. Milton, Reports on Progress in Physics, 69 (6), 16371711 (2006). 

[4] F. Rohrlich, Phys. Rev. 150, 1104, (1966) 

[5] D. Zwanziger, Phys. Rev. 3, 880 (1971). 

[6] S. Weinberg, Phys. Rev. 138, B988 (1965). 

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[7] L. D. Landau, E. M. Lifshitz, The Classical Theory of Fields , Fourth Edition: Volume 2 (Course of Theoretical Physics Series), (Pergamon Press, Oxford, 2000). 

[8] N. N. Bogoliubov, D. V. Shirkov, Introduction to the theory of quantized fields , (Wiley, New York, 1980). 

[9] J. . Schouten, Tensor analysis for physicists , (Clarendon Press, Oxford, 1951). 

