1. A. F. Timan, Theory of Approximation of the Functions of Real Variable [in Russian], Fizmatgiz, Moscow (1960).
2. V. K. Dzyadyk, Introduction to the Theory of Uniform Approximation of Functions [in Russian], Nauka, Moscow (1977).
3. N. P. Korneichuk, Exact Constants in Approximation Theory [in Russian], Nauka, Moscow (1987).
4. A. I. Stepanets, Methods of Approximation Theory [in Russian], Vol. 1, Institute of Mathematics, Ukrainian National Academy of Sciences, Kiev (2002).
5. A. I. Stepanets, Methods of Approximation Theory [in Russian], Vol. 2, Institute of Mathematics, Ukrainian National Academy of Sciences, Kiev (2002).