1. F. M. Korkmasov, “Approximative Properties of the de la Vallee-Poussin Sums for Discrete Fourier-JacobiSums,” Sib. Mat. Zh. 45, 334–355 (2004).
2. P. K. Suetin, Orthogonal Polynomials in Two Variables (Gordon and Breach, Amsterdam, 1999).
3. A. I. Yanushauskas, Multiple Trigonometric Series (Nauka, Novosibirsk, 1986) [in Russian].
4. I. K. Daugavet, “On the Lebesgue Constants for Double Fourier Series,” in Methods of Computation (Leningrad. Gos. Univ., Leningrad, 1970), Vol. 6, pp. 8–13 [in Russian].
5. O. I. Kuznetsova, “The Asymptotic Behavior of the Lebesgue Constants for a Sequence of Triangular Partial Sums of Double Fourier Series,” Sib. Mat. Zh. 18, 629–636 (1977) [Sib. Math. J. 18, 449–454 (1977)].