1. G. Alexits,Convergence problems of orthogonal series Pergamon Press (Oxford-New York 1961).
2. V. S. Fedulov, On (C, 1, 1)-summability of a double orthogonal series,Ukrain. Mat. Ž.,7 (1955), 433–442 (Russian).
3. F. Mℜicz, Moment inequalities and the strong laws of large numbers,Z. Wahrschein. verw. Geb.,35 (1976), 299–314.
4. F. Mŕicz, On the growth order of the rectangular partial sums of multiple non-orthogonal series,Analysis Math.,6 (1980), 327–341.
5. K. Tandori, über die orthogonalen Funktionen. I,Acta Sci. Math. (Szeged),18 (1957), 57–130.