1. R.A.Adams, Sobolev Spaces. Academic Press, New York, (1975).
2. O.V.Besov, V.P.Il'in, S.M.Nikol'sky. Integral representations of functions and embedding theorems. Nauka, Moscow, (1975).
3. V.I.Burenkov, About additivity of spacesw p r andB p r and about embedding theorems for general domains. Trudi Mat. In-ta. Steklova, 105, (1969), 30?44.
4. S.Campanato. Il teorema di immersione di Sobolev per una classe di apertinon dotati della proprieta di como. Ric. di Mat., 11, 1 (1962), 103?122.
5. L.E.Fraenkel. On regularity of the boundary in the theory of Sobolev spaces. Proc. London Math. Soc., 39 (1979), 385?427.