1. Bojanic, R., A Note on the Precision of Interpolation by Hermite—Fejér Polynomials In: Approximation Theory (Proc. Conf. Constructive Theory of Functions Budapest 1969; ed. by G. Alexits, S.B. Steckin), 69–76.
2. Butzer, P. L. and Nessel, R. J., Fourier Analysis and Approximation (Vol.1), Birkhä user Verlag, 1970.
3. Ditzian, Z. and Totik, V., Moduli of Smoothness, Springer-Verlag, 1987.
4. Fejér, L., Uber Interpolation, Götinger Nachrichten, (1)(1916), 66–91.
5. Gonska, H. H., Quantitative Aussagen zur Approximation Durch Positive Lineare Operatoren, Dissertation, Universität Duisburg, 1979.