1. Bari, N.K.: A Treatise on Trigonometric Series. Pergamon Press, New York (1965)
2. Bari, N.K., Stečkin, S.B.: Best approximations and differential properties of two conjugate functions. Trudy Mosk. Mat. Obšč. 5, 483–522 (1956)
3. Boas, R.P.: Quelques généralisations d’un théorème de S. Bernstein sur la dérivée d’un polynômetrigonométrique. C. R. Acad. Sci. Paris 227, 618–619 (1948) (in French)
4. Boas Jr., R.P.: Integrability Theorems for Trigonometric Transforms. Springer, New York (1967)
5. Butzer, P.L., Dyckhoff, H., Göerlich, E., Stens, R.L.: Best trigonometric approximation, fractional order derivatives and Lipschitz classes. Can. J. Math. 29, 781–793 (1977)