Approximation by Nörlund means of double Fourier series for Lipschitz functions

We study the rate of uniform approximation by Nörlund means of the rectangular partial sums of the double Fourier series of a function |(x, y) belonging to the class Lip α, 0 < α 1, on the two-dimensional torus −π < x, y π. As a special case we obtain the rate of uniform approximation by double Cesàro means.