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A new type of orthogonality for normed planes

Horst Martini, Margarita Spirova (2010)

Czechoslovak Mathematical Journal

In this paper we introduce a new type of orthogonality for real normed planes which coincides with usual orthogonality in the Euclidean situation. With the help of this type of orthogonality we derive several characterizations of the Euclidean plane among all normed planes, all of them yielding also characteristic properties of inner product spaces among real normed linear spaces of dimensions d 3 .

A nonlinear Banach-Steinhaus theorem and some meager sets in Banach spaces

Jacek Jachymski (2005)

Studia Mathematica

We establish a Banach-Steinhaus type theorem for nonlinear functionals of several variables. As an application, we obtain extensions of the recent results of Balcerzak and Wachowicz on some meager subsets of L¹(μ) × L¹(μ) and c₀ × c₀. As another consequence, we get a Banach-Mazurkiewicz type theorem on some residual subset of C[0,1] involving Kharazishvili's notion of Φ-derivative.

A note on Banach spaces with 1 -saturated duals

Denny H. Leung (1996)

Commentationes Mathematicae Universitatis Carolinae

It is shown that there exists a Banach space with an unconditional basis which is not c 0 -saturated, but whose dual is 1 -saturated.

A note on complex interpolation of Banach lattices

Anita Tabacco Vignati, Marco Vignati (1987)

Atti della Accademia Nazionale dei Lincei. Classe di Scienze Fisiche, Matematiche e Naturali. Rendiconti Lincei. Matematica e Applicazioni

We complete a result of Hernandez on the complex interpolation for families of Banach lattices.

A note on Dunford-Pettis like properties and complemented spaces of operators

Ioana Ghenciu (2018)

Commentationes Mathematicae Universitatis Carolinae

Equivalent formulations of the Dunford-Pettis property of order p ( D P P p ), 1 < p < , are studied. Let L ( X , Y ) , W ( X , Y ) , K ( X , Y ) , U ( X , Y ) , and C p ( X , Y ) denote respectively the sets of all bounded linear, weakly compact, compact, unconditionally converging, and p -convergent operators from X to Y . Classical results of Kalton are used to study the complementability of the spaces W ( X , Y ) and K ( X , Y ) in the space C p ( X , Y ) , and of C p ( X , Y ) in U ( X , Y ) and L ( X , Y ) .

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