1. Yu. N. Demkov:Variational Principles in the Theory of Collisions (New York, N. Y., 1963). AlsoF. Calogero:Variable Phase Approach to Potential Scattering (New York, N. Y., 1967)
2. S. R. Singh:Lett. Nuovo Cimento,7, 493 (1973).B. L. Moiseiwitsch:Proc. Phys. Soc.,86, 737 (1965)
3. The Padé Approximants in Theoretical Physics, edited byG. A. Baker jr. andG. L. Gammel (New York, N. Y., 1970).
4. J. Nuttal: in ref. (3),The Padé Approximants in Theoretical Physics, edited byG. A. Baker jr. andG. L. Gammel (New York, N. Y., 1970). p. 219;C. R. Garibotti:Ann. of Phys.,71, 486 (1972).
5. See,e.g. R. Sugar andR. Blankenbecler:Phys. Rev.,136, B 472 (1964),S. Weinberg:Phys. Rev.,133, B 232 (1964);M. Scadron, S. Weinberg andJ. Wright:Phys. Rev.,135, B 202 (1964).