1. Yu. N. Subbotin, “On the connection between finite differences and corresponding derivatives,” Tr. Mat. Inst., Akad. Nauk SSSR,78, 24–42 (1965).
2. I. J. Schoenberg, “Cardinal spline interpolation,” CBMS Regional Conference,12, S.I.A.M., Philadelphia (1973).
3. I. J. Schoenberg, “On Charles Micchelli's theory of cardinal L-splines,” MRC Report 1511, 1975. Studies in Splines and Approx. Theory, Academic Press (1976).
4. C. A. Micchelli, “Cardinal L-splines,” Studies in Splines and Approx. Theory, Academic Press (1976).
5. C. L. Siegel, Transcendental Numbers, Annals of Math. Studies, No. 16, Princeton University Press, Princeton, New Jersey (1949).