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Sharp embeddings of Besov spaces with logarithmic smoothness.

Petr GurkaBohumir Opic — 2005

Revista Matemática Complutense

We prove sharp embeddings of Besov spaces B with the classical smoothness σ and a logarithmic smoothness α into Lorentz-Zygmund spaces. Our results extend those with α = 0, which have been proved by D. E. Edmunds and H. Triebel. On page 88 of their paper (Math. Nachr. 207 (1999), 79-92) they have written: ?Nevertheless a direct proof, avoiding the machinery of function spaces, would be desirable.? In our paper we give such a proof even in a more general context. We cover both the...

Compactness of Hardy-type integral operators in weighted Banach function spaces

David EdmundsPetr GurkaLuboš Pick — 1994

Studia Mathematica

We consider a generalized Hardy operator T f ( x ) = ϕ ( x ) ʃ 0 x ψ f v . For T to be bounded from a weighted Banach function space (X,v) into another, (Y,w), it is always necessary that the Muckenhoupt-type condition = s u p R > 0 ϕ χ ( R , ) Y ψ χ ( 0 , R ) X ' < be satisfied. We say that (X,Y) belongs to the category M(T) if this Muckenhoupt condition is also sufficient. We prove a general criterion for compactness of T from X to Y when (X,Y) ∈ M(T) and give an estimate for the distance of T from the finite rank operators. We apply the results to Lorentz spaces and characterize...

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