1. B. I. Golubov, Series with respect to the Haar system, Itogi Nauki Ser. Mat. Anal., 1971, 109–146 (in Russian); translated in J. Soviet Math., 1 (1973), 704–726.
2. A. D. Ebralidze, On uniqueness of multiple Haar series, Soob. Akad. Nauk Gruz. SSR, 1973, 537–539 (in Russian).
3. B. S. Kashin and A. A. Saakyan, Orthogonal series, 2nd ed., AFC Publishers Moscow, 1999) (in Russian); English transl. of 1st ed., Transl. Math. Monographs, vol. 75, Amer. Math. Soc. (Providence, RI, 1989).
4. Kh. O. Movsisyan, On the uniqueness of double series with respect to systems of Haar and Walsh series, Izv. Akad. Nauk Arm. SSR Mat., 9 (1974), 40–61 (in Russian).
5. M. G. Plotnikov, On uniqueness of everywhere convergent multiple Haar series, Vestnik Moskov. Univ. Ser. I Mat. Mekh., 2001, 23–28 (in Russian); translated in Moscow Univ. Math. Bull., 56 (2001), 24–29.