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ℱ-bases with brackets and with individual brackets in Banach spaces

Tomasz Kochanek — 2012

Studia Mathematica

We provide a partial answer to the question of Vladimir Kadets whether given an ℱ-basis of a Banach space X, with respect to some filter ℱ ⊂ 𝒫(ℕ), the coordinate functionals are continuous. The answer is positive if the character of ℱ is less than 𝔭. In this case every ℱ-basis is an M-basis with brackets which are determined by an element of ℱ.

An inconsistency equation involving means

Roman GerTomasz Kochanek — 2009

Colloquium Mathematicae

We show that any quasi-arithmetic mean A φ and any non-quasi-arithmetic mean M (reasonably regular) are inconsistent in the sense that the only solutions f of both equations f ( M ( x , y ) ) = A φ ( f ( x ) , f ( y ) ) and f ( A φ ( x , y ) ) = M ( f ( x ) , f ( y ) ) are the constant ones.

Uncountable sets of unit vectors that are separated by more than 1

Tomasz KaniaTomasz Kochanek — 2016

Studia Mathematica

Let X be a Banach space. We study the circumstances under which there exists an uncountable set 𝓐 ⊂ X of unit vectors such that ||x-y|| > 1 for any distinct x,y ∈ 𝓐. We prove that such a set exists if X is quasi-reflexive and non-separable; if X is additionally super-reflexive then one can have ||x-y|| ≥ slant 1 + ε for some ε > 0 that depends only on X. If K is a non-metrisable compact, Hausdorff space, then the unit sphere of X = C(K) also contains such a subset; if moreover K is perfectly...

Probability distribution solutions of a general linear equation of infinite order

Tomasz KochanekJanusz Morawiec — 2009

Annales Polonici Mathematici

Let (Ω,,P) be a probability space and let τ: ℝ × Ω → ℝ be strictly increasing and continuous with respect to the first variable, and -measurable with respect to the second variable. We obtain a partial characterization and a uniqueness-type result for solutions of the general linear equation F ( x ) = Ω F ( τ ( x , ω ) ) P ( d ω ) in the class of probability distribution functions.

Probability distribution solutions of a general linear equation of infinite order, II

Tomasz KochanekJanusz Morawiec — 2010

Annales Polonici Mathematici

Let (Ω,,P) be a probability space and let τ: ℝ × Ω → ℝ be a mapping strictly increasing and continuous with respect to the first variable, and -measurable with respect to the second variable. We discuss the problem of existence of probability distribution solutions of the general linear equation F ( x ) = Ω F ( τ ( x , ω ) ) P ( d ω ) . We extend our uniqueness-type theorems obtained in Ann. Polon. Math. 95 (2009), 103-114.

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