1. P. L. Ul’yanov, ‘‘Weyl factors for unconditional convergence,’’ Mat. Sb. (N.S.) 60, 39–62 (1963). https://www.mathnet.ru/eng/sm4535.
2. P. L. Ul’yanov, ‘‘Divergent Fourier series,’’ Russ. Math. Surv. 16 (3), 1–75 (1961). https://doi.org/10.1070/RM1961v016n03ABEH001119
3. G. G. Gevorkyan, ‘‘Weyl multipliers for the unconditional convergence of series in a Franklin system,’’ Math. Notes 41, 446–451 (1987). https://doi.org/10.1007/BF01158385
4. S. Kachmazh and G. Shteingauz, Theory of Orthogonal Series (Fizmatgiz, Moscow, 1958).
5. P. L. Ul’yanov, ‘‘The divergence of series obtained using the Haar system and using bases,’’ Sov. Math., Dokl. 2, 679–682 (1961).