1. BaetemanM.L. and ChadanK., Annales de l'I.H.P. A XXIV, 1 (1976).
2. SchwingerJ., Proc. Nat. Acad. Sci. U.S. 47, 122 (1961).
3. BirmanM.S., Mat. Sb. 55, 125 (1961); Eng. Trans. AMS Trans. 53, 23 (1966).
4. NewtonR.G., Scattering Theory of Waves and Particles, McGraw-Hill, New York, 1966, chap. 12.
5. See ref. [1], formula (23) with k=0.