Published online by Cambridge University Press: 20 November 2018
The extension of the Rellich-Kondrachov theorem on the complete continuity of Sobolev space imbeddings of the sort
1
to unbounded domains G has recently been under study [1–5] and this study has yielded [4] a condition on G which is necessary and sufficient for the compactness of (1). Similar compactness theorems for the imbeddings
2
are well known for bounded domains G with suitably regular boundaries, and the question naturally arises whether any extensions to unbounded domains can be made in this case.