1. H. Triebel,Theory of Function Spaces [Russian translation], Mir, Moscow (1986).
2. B. Sendov,Hausdorff Approximations, Sofia (1979).
3. A. P. Petukhov, “Approximation of functions by singular integrals in the Hausdorff metric,”Mat. Sb.,135 (177), No. 2, 235–252 (1988).
4. S. M. Nikol'skii,Approximation of Functions of Several Variables and Imbedding Theorems [in Russian], Nauka, Moscow (1977).
5. O. V. Besov, V. P. Il'in, and C. M. Nikol'skii,Integral Representations of Functions and Imbedding Theorems [in Russian], Nauka, Moscow (1975).