A. I. Kozko, A. V. Rozhdestvenskii, “On Jackson's inequality for a generalized modulus of continuity in $L_2$”, Sb. Math., 195:8 (2004), 1073–1115
E. E. Berdysheva, “Optimal Set of the Modulus of Continuity in the Sharp Jackson Inequality in the Space $L_2$”, Math. Notes, 76:5 (2004), 620–627
A. I. Kozko, A. V. Rozhdestvenskii, “On Jackson's Inequality for Generalized Moduli of Continuity”, Math. Notes, 73:5 (2003), 736–741
S. B. Vakarchuk, “On Best Polynomial Approximations in $L_2$”, Math. Notes, 70:3 (2001), 300–310
M. G. Esmaganbetov, “Widths of classes from $L_2[0,2\pi]$ and the minimization of exact constants in Jackson-type inequalities”, Math. Notes, 65:6 (1999), 689–693
A. G. Babenko, N. I. Chernykh, V. T. Shevaldin, “The Jackson–Stechkin inequality in $L^2$ with a trigonometric modulus of continuity”, Math. Notes, 65:6 (1999), 777–781
E. E. Berdysheva, “Two related extremal problems for entire functions of several variables”, Math. Notes, 66:3 (1999), 271–282
V. A. Yudin, “An extremum problem for distribution functions”, Math. Notes, 63:2 (1998), 279–282
A. G. Babenko, “An exact Jackson–Stechkin inequality for $L^2$-approximation on the interval with the Jacobi weight and on projective spaces”, Izv. Math., 62:6 (1998), 1095–1119
V. A. Yudin, “Lower bounds for spherical designs”, Izv. Math., 61:3 (1997), 673–683
A. G. Babenko, “Sharp Jackson–Stechkin inequality in $L^2$ for multidimensional spheres”, Math. Notes, 60:3 (1996), 248–263
V. A. Yudin, “Two external problems for trigonometric polynomials”, Sb. Math., 187:11 (1996), 1721–1736
V. I. Ivanov, “Approximation of functions in spaces $L_p$”, Math. Notes, 56:2 (1994), 770–789
V. I. Ivanov, “On the approximation of functions in spaces $L_p$”, Math. Notes, 54:2 (1993), 872–875
V. I. Ivanov, “Approximation in $L_p$ by polynomials in the Walsh system”, Math. USSR-Sb., 62:2 (1989), 385–402
N. P. Korneichuk, “On extremal problems in the theory of best approximation”, Russian Math. Surveys, 29:3 (1974), 7–43