1. A. Zygmund,Trigonometric Series, 2nd ed., Cambridge Univ. Press, Cambridge (1959).
2. É. S. Belinskii, in:Metric Problems of the Theory of Functions and Mappings [in Russian], Naukova Dumka, Kiev (1975), pp. 15–23.
3. R. M. Trigub, in:The Theory of Functions and Mappings [in Russian], Naukova Dumka, Kiev (1979), pp. 149–173.