1. A. Bastai, L. Bertocchi, S. Fubini, G. Furlan andM. Tonin:Nuovo Cimento,30, 1512, 1532 (1963);W. Guttinger, R. Penzl andE. Pfaffelhuber:Ann. of Phys.,33, 246 (1965);Nuovo Cimento,35, 1247 (1965);H. H. Aly andJ. G. Taylor:Journ. Math. Phys.,9, 781 (1968).
2. R. M. Spector:Journ. Math. Phys.,8, 2357 (1967).
3. See, for example,E. Coddington andN. Levinson:Theory of Ordinary Differential Equations (New York, 1955);P. Hartman:Ordinary Differential Equations (New York, 1964), p. 370, Theorem 8.1;R. Bellman:Stability Theory of Differential Equations (New York, 1954);V. de Alfaro andT. Regge:Potential Scattering (Amsterdam, 1965).
4. See, for example,T. Kato:Comm. Pure Appl. Math.,12, 403 (1959).
5. G. Watson:Theory of Bessel Functions, 2nd Edition (London, 1944), p. 78.