1. V. K. Dzyadyk, Introduction to the Theory of Uniform Approximation of Functions by Polynomials (Nauka, Moscow, 1977) [in Russian].
2. M. G. Pleshakov, “Comonotone Jackson’s inequality,” J. Approx. Theory 99(2), 409–421 (1999).
3. M. G. Pleshakov, Comonotone approximation of Periodic Functions of Sobolev Classes, Candidate’s Dissertation in Mathematics and Physics (Saratov State University, Saratov, 1997) [in Russian].
4. A. S. Shvedov, “Comonotone approximation of functions by polynomials,” Dokl. Akad. Nauk SSSR 250(1), 39–42 (1980) [Soviet Math. Dokl. 21, 34–37 (1980)].
5. A. S. Shvedov, “Orders of coapproximations of functions by algebraic polynomials,” Mat. Zametki 29(1), 117–130 (1981).