1. A. I. Stepanets, ?Classes of periodic functions and the approximation of their elements by Fourier sums,? Dokl. Akad. Nauk SSSR,277, No. 5, 1074?1077 (1984).
2. A. I. Stepanets, ?Classification of periodic functions and the rate of convergence of their Fourier series,? Izv. Akad. Nauk SSSR, Ser. Mat.,50, No. 1, 101?136 (1986).
3. A. I. Stepanets, ?Deviations of Fourier sums on classes of infinitely differentiable functions,? Ukr. Mat. Zh.,36, No. 6, 750?758 (1984).
4. N. I. Akhiezer, Elements of the Theory of Elliptic Functions [in Russian], Nauka, Moscow (1970).
5. A. N. Kolmogorov, ?Zur Grössenordnung des Restliedes Fourierschen Reihen differenzierbaren Funktionen,? Ann. Math.,36, 521?626 (1935).