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2. Gordon and Breach, New York, 1963.
3. F.V. Atkinson Discrete and Continuous Boundary Problems, Academic Press, New York, 1964.
4. O. Blumenthal Über die Entwicklung einer willkurlichen Funktion nach dennennern des Kettenbruches für $ [?(?)/(z-?)] d?; Inaugural Dissertation, Gottingen, 1898
5. K.M. Case,‘Orthogonal Polynomials revisited’, in “Theory and Application of Special Functions” (R.A. Askey, ed.), Academic Press, New York, 1975, pp. 289–304.