Barut, A. O. and J. Nagel.
Text: "Perturbation theory for infinite-component wave equations." New covariant perturbation theory for infinite-component wave equations, which leads to group elements and can be studied in closed form. Journal of Physics A: Mathematical and General. 10(7), July, 1977. p. 1243-1247.
See Also: foundations of physics, quantum electrodynamics, perturbation theory.
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