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2. V. V. Arestov and E. E. Berdysheva, Turán’s problem for positive definite functions with supports in a hexagon, Trudy Inst. Mat. Mekh., 7 (2001), 21–29 (in Russian); translated in Proc. Steklov Inst. Math., Suppl. 1 (2001), S20–S29.
3. V. V. Arestov and E. E. Berdysheva, The Turán problem for a class of polytopes, East J. Approx., 8 (2002), 381–388.
4. E. E. Berdysheva and H. Berens, On a discrete Turán problem for l1 radial functions, in: New Perspectives on Approximation and Sampling Theory–Festschrift in honor of Paul Butzer’s 85th birthday, Ed. by G. Schmeisser and A. Zayed, Applied and Numerical Harmonic Analysis, Birkhauser (2014), pp. 447–468.
5. R. P. Boas, Jr. and M. Kac, Inequalities for Fourier transforms of positive functions, Duke Math. J., 12 (1945), 189–206.