1. S. B. Vakarchuk, "Generalized characteristics of smoothness and some extreme problems of the approximation theory of functions in the space L 2(ℝ). I," Ukr. Mat. Zh., 70, No. 9, 1166-1191 (2018)
2. English translation : Ukr. Math. J., 70, No 9, 1345-1374 (2019).
3. S. B. Vakarchuk, "Jackson-type inequalities with generalized modulus of continuity and exact values of the n-widths for the classes of (ψ , β)-differentiable functions in L 2 . I," Ukr. Mat. Zh., 68, No 6, 723-745 (2016)
4. English translation : Ukr. Math. J., 68, No 6, 823-848 (2016).
5. S. B. Vakarchuk, "Jackson-type inequalities with generalized modulus of continuity and exact values of the n-widths for the classes of (ψ, β)-differentiable functions in L 2 . II," Ukr. Mat. Zh., 68, No. 8, 1021-1036 (2016)