1. Abel, U., An identity for a general class of approximation operators, J. Approx. Theory, 142, pp. 20–35, 2006, http://doi.org/10.1016/j.jat.2006.03.005
2. Abel, U., Gupta, V. and Ivan, M., The complete asymptotic expansion for a general Durrmeyer variant of the Meyer-Konig and Zeller operators Math. Comput. Modelling 40, no. 7-8, pp. 867–875, 2004, http://doi.org/10.1016/j.mcm.2004.10.016
3. Abel, U. and Ivan, M., Durrmeyer variants of the Bleimann, Butzer and Hahn operators, Mathematical analysis and approximation theory, Burg, Sibiu, pp. 1–8, 2002.
4. Abel, U. and Ivan, M., Enhanced asymptotic approximation ans approximation of truncated functions by linear operators, Constructive Theory of Functions, Proceedings of the International Conference on Constructive Theory of Functions, Varna, June 2 - June 6, 2005, B. D. Bojanov (Ed.), Prof. Marin Drinov Academic Publishing House, pp. 1–10, 2006.
5. Baskakov V. A., An instance of a sequence of positive linear operators in the space of continuous functions, Doklady Akademii Nauk SSSR, 113:2, pp. 249–251, 1957.