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On prequojections and their duals.

M. I. Ostrovskii (1998)

Revista Matemática Complutense

The paper is devoted to the class of Fréchet spaces which are called prequojections. This class appeared in a natural way in the structure theory of Fréchet spaces. The structure of prequojections was studied by G. Metafune and V. B. Moscatelli, who also gave a survey of the subject. Answering a question of these authors we show that their result on duals of prequojections cannot be generalized from the separable case to the case of spaces of arbitrary cardinality. We also introduce a special class...

On r -reflexive Banach spaces

Iryna Banakh, Taras O. Banakh, Elena Riss (2009)

Commentationes Mathematicae Universitatis Carolinae

A Banach space X is called r -reflexive if for any cover 𝒰 of X by weakly open sets there is a finite subfamily 𝒱 𝒰 covering some ball of radius 1 centered at a point x with x r . We prove that an infinite-dimensional separable Banach space X is -reflexive ( r -reflexive for some r ) if and only if each ε -net for X has an accumulation point (resp., contains a non-trivial convergent sequence) in the weak topology of X . We show that the quasireflexive James space J is r -reflexive for no r . We do not know...

On regularization in superreflexive Banach spaces by infimal convolution formulas

Manuel Cepedello-Boiso (1998)

Studia Mathematica

We present here a new method for approximating functions defined on superreflexive Banach spaces by differentiable functions with α-Hölder derivatives (for some 0 < α≤ 1). The smooth approximation is given by means of an explicit formula enjoying good properties from the minimization point of view. For instance, for any function f which is bounded below and uniformly continuous on bounded sets this formula gives a sequence of Δ-convex C 1 , α functions converging to f uniformly on bounded sets and...

On restricted weak upper semicontinuous set valued mappings and reflexivity

Julio Benítez, Vicente Montesinos (1999)

Bollettino dell'Unione Matematica Italiana

È noto che se uno spazio di Banach è quasi-smooth (cioè, la sua applicazione di dualità è debolmente semicontinua superiormente in senso ristretto), allora il suo duale non ha sottospazi chiusi normanti propri. Inoltre, se uno spazio di Banach ha una norma equivalente la cui applicazione di dualità ha un grafo che contiene superiormente un'applicazione debolmente semicontinua superiormente in senso ristretto, allora lo spazio è Asplund. Dimostriamo che se uno spazio di Banach ha una norma equivalente...

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