1. N. K. Bari, Trigonometric Series [in Russian], Fizmatgiz, Moscow (1961).
2. P. L. Ul'yanov, ?On series with respect to a Haar system with monotone coefficients,? Izv. Akad. Nauk SSSR, Ser. Mat.,28, No. 4, 925?950 (1964).
3. A. A. Shneider, ?On series with respect to Walsh functions with monotone coefficients,? Izv. Akad. Nauk SSSR, Ser. Mat.,12, No. 2, 179?192 (1948).
4. S. Kaczmarz and H. Steinhaus Theory of Orthogonal Series [Russian translation], Fizmatgiz, Moscow (1958).
5. M. B. Petrovskaya, ?On series with respect to a Harr system,? Dissertation [in Russian], Moscow (1966).