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2. V. K. Dzyadyk, Introduction to the Theory of Uniform Approximation of Functions [in Russian], Nauka, Moscow (1977).
3. N. P. Korneichuk, Extremal Problems in Approximation Theory [in Russian], Nauka, Moscow (1976).
4. P.-J. Laurent, Approximation et Optimisation [Russian translation], Mir, Moscow (1975).
5. A. I. Stepanets, Methods of Approximation Theory [in Russian], Vol. 1, Institute of Mathematics, Ukrainian Academy of Sciences, Kiev (2002).