We study extension operators on Sobolev spaces with decreasing integrability on the base of set functions associated with the operator norms. Sharp necessary conditions in the terms of the weak density condition and the terms of weak equivalence of Euclidean and intrinsic metrics are given.
On the constants for multiplication in Sobolev spaces
Sobolev spaces on Lie groups: embedding theorems and algebra properties
New results on multiplication in Sobolev spaces
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