Double trigonometric series with lacunar sign-constant coefficients / A. Zh. Ydyrys. //Vestnik Moskovskogo Universiteta. Seriya 1. Matematika. Mekhanika. 2012. ? 6. P. 33-35 [Moscow Univ. Math. Bulletin. Vol. 67, N 6, 2012.].

The article presents an analogue of Sidon's theorem for series of the form ∑^∞_k=1 ∑^∞_n=0a_k,n cosm_kx cosny, where the coefficients a_k,n have a constant sign for any fixed k.

Key words: double trigonometric series, lacunary series, Sidon's theorem.