1. Anthony, G.: 1957, ?Hanford Atomic Products Operation?, Rep. H.W.-49180.
2. Arthurs, A. M.: 1970,Complementary Variational Principles, Clarendon Press, Oxford.
3. Baker, G. A., Jr.: 1975,J. Math. Phys. 16, 813.
4. Chandrasekhar, S.: 1960,Radiative Transfer, Dover Publ., New York.
5. Elwakil, S. A.: 1980,J. Phys. D13, 339.