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Normed algebras of differentiable functions on compact plane sets: completeness and semisimple completions

Heiko Hoffmann (2011)

Studia Mathematica

We continue the study of the completeness and completions of normed algebras of differentiable functions Dⁿ(K) (where K is a perfect, compact plane set), initiated by Bland, Dales and Feinstein [Studia Math. 170 (2005) and Indian J. Pure Appl. Math. 41 (2010)]. We prove new characterizations of the completeness of D¹(K) and results concerning the semisimplicity of the completion of D¹(K). In particular, we prove that semi-rectifiability is necessary for the completion of D¹(K) to be semisimple in...

On a -Kasch spaces

Ali Akbar Estaji, Melvin Henriksen (2010)

Archivum Mathematicum

If X is a Tychonoff space, C ( X ) its ring of real-valued continuous functions. In this paper, we study non-essential ideals in C ( X ) . Let a be a infinite cardinal, then X is called a -Kasch (resp. a ¯ -Kasch) space if given any ideal (resp. z -ideal) I with gen ( I ) < a then I is a non-essential ideal. We show that X is an 0 -Kasch space if and only if X is an almost P -space and X is an 1 -Kasch space if and only if X is a pseudocompact and almost P -space. Let C F ( X ) denote the socle of C ( X ) . For a topological space X with only...

On certain products of Banach algebras with applications to harmonic analysis

Mehdi Sangani Monfared (2007)

Studia Mathematica

Given Banach algebras A and B with spectrum σ(B) ≠ ∅, and given θ ∈ σ(B), we define a product A × θ B , which is a strongly splitting Banach algebra extension of B by A. We obtain characterizations of bounded approximate identities, spectrum, topological center, minimal idempotents, and study the ideal structure of these products. By assuming B to be a Banach algebra in ₀(X) whose spectrum can be identified with X, we apply our results to harmonic analysis, and study the question of spectral synthesis,...

On dense ideals of C*-algebras and generalizations of the Gelfand-Naimark Theorem

Jorma Arhippainen, Jukka Kauppi (2013)

Studia Mathematica

We develop the theory of Segal algebras of commutative C*-algebras, with an emphasis on the functional representation. Our main results extend the Gelfand-Naimark Theorem. As an application, we describe faithful principal ideals of C*-algebras. A key ingredient in our approach is the use of Nachbin algebras to generalize the Gelfand representation theory.

On multiplication in spaces of continuous functions

Marek Balcerzak, Aleksander Maliszewski (2011)

Colloquium Mathematicae

We introduce and examine the notion of dense weak openness. In particular we show that multiplication in C(X) is densely weakly open whenever X is an interval in ℝ.

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