1. B. F. Logan, “Extremal problems for positive-definite bandlimited functions. II. Eventually negative functions,”SIAM J. Math. Anal.,14, No. 2, 253–257 (1983).
2. N. I. Chernykh, “Jackson's inequality inL 2,”Trudy Mat. Inst. Steklov [Proc. Steklov Inst. Math.],88, 71–74 (1967).
3. N. I. Chernykh, “The best approximation of periodic functions by trigonometric polynomials inL 2,”Mat. Zametki [Math. Notes],2, No. 5, 513–522 (1967).
4. V. A. Yudin, “The multidimensional Jackson theorem inL 2,”Mat. Zametki [Math. Notes],29, No. 2, 309–315 (1981).
5. V. V. Arestov and N. I. Chernykh, “On theL 2-approximation of periodic functions by trigonometric polynomials,” in:Approximation and Function Spaces (Gdansk, 1979), North-Holland, Amsterdam (1981), pp. 25–43.