1. A. N. Kolmogorov, Sur les fonctions harmoniques conjuguées et les séries de Fourier [On conjugate harmonic functions and Fourier series]. Fundam. Math.,7, 23?28 (1925).
2. C. H. Hardy and I. E. Littlewood, A convergence criterion for Fourier series, Math. Z.,28, No. 4, 612?634(1928).
3. K. Iano, On Hardy and Littlewood's theorem, Proc. Jap. Acad.,33, No. 2, 73?74 (1957).
4. M. Sato, Uniform convergence of Fourier series, IV, Proc. Jap. Acad.,31, No. 5, 261?263 (1955).
5. P. L. Ul'yanov, On the approximation of a function, Sib. Matem. Zh.,5, No. 2, 418?437 (1964).