1. On double orthogonal series;Agnew,1932
2. Convergence, uniqueness, and summability of multiple trigonometric series;Ash;Trans. Amer. Math. Soc.,1972
3. Some methods of summability of double series and double integrals;Chelidze;Tbilisi,1977
4. On (C, 1, 1)-summability of double orthogonal series;Fedulov;Ukrain Mat. Zh.,1955
5. Note on the strong summability of series;Hyslop,1952