1. N. I. Achiezer, Theory of Approximation, Fredrick Ungar, New York, 1956.
2. J. H. Ahlberg, E. N. Nilson and J. L. Walsh, Fundamental Properties of Generalized Splines,Proc. Nat. Acad. Sci. 52 (1964), 1412–1419.
3. Tom M. Apostol, Mathematical Analysis, Addison-Wesley, Reading, Mass., 1958.
4. V. Gantmacher and M. Krein,Oszillationsmatrizen, Oszillationskerne und kleine Schwingungen Mechanischer Systeme, Akademie-Verlag, Berlin, 1960.
5. T. N. E. Greville, Interpolation by Generalized Spline Functions, MRC Tech. Rep. 476, University of Wisconsin, May 1964.