Besov, Oleg Vladimirovič; Kufner, Alois:
О плотности гладких функции в весовых пространствах.
(Russian) [The density of smooth functions in weight spaces].Czechoslovak Mathematical Journal,
vol. 18
(1968),
issue 1,
pp. 178-188
Nečas, Jindřich:
Об областях типа ${\frak N}$.
(Russian) [On domains of type ${\frak N}$].Czechoslovak Mathematical Journal,
vol. 12
(1962),
issue 2,
pp. 274-287