1. A. F. Timan, Theory of Approximation of Functions of a Real Variable [in Russian], Fizmatgiz, Moscow (1960).
2. H. Lebesgue, ?Sur les intégrales singulières,? Ann. Fac. Sci. Univ. Toulouse Sci. Math. Sci. Phys.,?1, No. 3, 25?117 (1909).
3. S. M. Nikol'skii, ?On linear methods of summation of Fourier series,? Izv. Akad. Nauk SSSR, Ser. Mat.,12, No. 3, 259?278 (1948).
4. B. Nagy, ?Methodes de sommation des series de Fourier. I,? Acta Sci. Math. Szeged,12, Part B, 204?210 (1950).
5. J. Kramata and M. Tomic, ?Sur la sommation des series de Fourier,? Glas Srpske Akademije Nauka. Odelijenie Prirodno-Matemati?kih Nauka (Belgrade),206, No. 5, 89?126 (1953).