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On the linear Denjoy property of two-variable continuous functions

Miklós Laczkovich, Ákos K. Matszangosz (2015)

Colloquium Mathematicae

The classical Denjoy-Young-Saks theorem gives a relation, here termed the Denjoy property, between the Dini derivatives of an arbitrary one-variable function that holds almost everywhere. Concerning the possible generalizations to higher dimensions, A. S. Besicovitch proved the following: there exists a continuous function of two variables such that at each point of a set of positive measure there exist continuum many directions, in each of which one Dini derivative is infinite and the other...

On the points of non-differentiability of convex functions

David Pavlica (2004)

Commentationes Mathematicae Universitatis Carolinae

We characterize sets of non-differentiability points of convex functions on n . This completes (in n ) the result by Zajíček [2] which gives a characterization of the magnitude of these sets.

On the range of the derivative of a real-valued function with bounded support

T. Gaspari (2002)

Studia Mathematica

We study the set f’(X) = f’(x): x ∈ X when f:X → ℝ is a differentiable bump. We first prove that for any C²-smooth bump f: ℝ² → ℝ the range of the derivative of f must be the closure of its interior. Next we show that if X is an infinite-dimensional separable Banach space with a C p -smooth bump b:X → ℝ such that | | b ( p ) | | is finite, then any connected open subset of X* containing 0 is the range of the derivative of a C p -smooth bump. We also study the finite-dimensional case which is quite different. Finally,...

On weakly Gibson F σ -measurable mappings

Olena Karlova, Volodymyr Mykhaylyuk (2013)

Colloquium Mathematicae

A function f: X → Y between topological spaces is said to be a weakly Gibson function if f ( Ū ) f ( U ) ¯ for any open connected set U ⊆ X. We prove that if X is a locally connected hereditarily Baire space and Y is a T₁-space then an F σ -measurable mapping f: X → Y is weakly Gibson if and only if for any connected set C ⊆ X with dense connected interior the image f(C) is connected. Moreover, we show that each weakly Gibson F σ -measurable mapping f: ℝⁿ → Y, where Y is a T₁-space, has a connected graph.

Optimal embeddings of critical Sobolev-Lorentz-Zygmund spaces

Hidemitsu Wadade (2014)

Studia Mathematica

We establish the embedding of the critical Sobolev-Lorentz-Zygmund space H p , q , λ , . . . , λ n / p ( ) into the generalized Morrey space Φ , r ( ) with an optimal Young function Φ. As an application, we obtain the almost Lipschitz continuity for functions in H p , q , λ , . . . , λ n / p + 1 ( ) . O’Neil’s inequality and its reverse play an essential role in the proofs of the main theorems.

Pettis integration

Musiał, Kazimierz (1985)

Proceedings of the 13th Winter School on Abstract Analysis

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