1. Bary, N.K., Stechkin, S.B.: Best approximation and differential properties of two conjugate functions. Trudy Mosk Mat Obs. 5, 483–522 (1956) ((in Russian))
2. Bary, N.K.: A Treatise on Trigonometric Series, vol. II. Macmillan, New York (1964)
3. Bustamante, J.: Direct and strong converse inequalities for approximation with Fejér means. Demonstr. Math. 53(1), 80–85 (2020)
4. Butzer, P.L., Pawelke, S.: Ableitungen yon trigonometrischen Approximationsprozessen. Acta Sci. Math. (Szeged) 28(1–2), 173–183 (1967)
5. Cruz-Uribe, D., Fiorenza, A.: Variable Lebesgue Spaces: Foundations and Harmonic Analysis, Applied and Numerical Harmonic Analysis. Birkhäuser, Heidelberg (2013)