1. Jordan C., “Sur la series de Fourier,” C. R. Math. Acad. Sci. Paris, 92, 228–230 (1881).
2. Chanturia Z. A., “The modulus of variation of a function and its application in the theory of Fourier series,” Soviet. Math. Dokl., 15, 67–71 (1974).
3. Dyachenko M. I., “Waterman classes and spherical partial sums of double Fourier series,” Anal. Math., 21, 3–21 (1995).
4. Dyachenko M. I., “Two-dimensional Waterman classes and u-convergence of Fourier series,” Sb. Math., 190, No. 7–8, 955–972 (1999).
5. Dyachenko M. I. and Waterman D., “Convergence of double Fourier series and W-classes,” Trans. Amer. Math. Soc., 357, 397–407 (2005).