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On z◦ -ideals in C(X)

F. Azarpanah, O. Karamzadeh, A. Rezai Aliabad (1999)

Fundamenta Mathematicae

An ideal I in a commutative ring R is called a z°-ideal if I consists of zero divisors and for each a ∈ I the intersection of all minimal prime ideals containing a is contained in I. We characterize topological spaces X for which z-ideals and z°-ideals coincide in , or equivalently, the sum of any two ideals consisting entirely of zero divisors consists entirely of zero divisors. Basically disconnected spaces, extremally disconnected and P-spaces are characterized in terms of z°-ideals. Finally,...

Operators determining the complete norm topology of C(K)

A. Villena (1997)

Studia Mathematica

For any uniformly closed subalgebra A of C(K) for a compact Hausdorff space K without isolated points and x 0 A , we show that every complete norm on A which makes continuous the multiplication by x 0 is equivalent to · provided that x 0 - 1 ( λ ) has no interior points whenever λ lies in ℂ. Actually, these assertions are equivalent if A = C(K).

Outer and inner vanishing measures and division in H∞ + C.

Keiji Izuchi (2002)

Revista Matemática Iberoamericana

Measures on the unit circle are well studied from the view of Fourier analysis. In this paper, we investigate measures from the view of Poisson integrals and of divisibility of singular inner functions in H∞ + C. Especially, we study singular measures which have outer and inner vanishing measures. It is given two decompositions of a singular positive measure. As applications, it is studied division theorems in H∞ + C.

Outers for noncommutative H p revisited

David P. Blecher, Louis E. Labuschagne (2013)

Studia Mathematica

We continue our study of outer elements of the noncommutative H p spaces associated with Arveson’s subdiagonal algebras. We extend our generalized inner-outer factorization theorem, and our characterization of outer elements, to include the case of elements with zero determinant. In addition, we make several further contributions to the theory of outers. For example, we generalize the classical fact that outers in H p actually satisfy the stronger condition that there exist aₙ ∈ A with haₙ ∈ Ball(A)...

Pervasive algebras and maximal subalgebras

Pamela Gorkin, Anthony G. O'Farrell (2011)

Studia Mathematica

A uniform algebra A on its Shilov boundary X is maximal if A is not C(X) and no uniform algebra is strictly contained between A and C(X). It is essentially pervasive if A is dense in C(F) whenever F is a proper closed subset of the essential set of A. If A is maximal, then it is essentially pervasive and proper. We explore the gap between these two concepts. We show: (1) If A is pervasive and proper, and has a nonconstant unimodular element, then A contains an infinite descending chain of pervasive...

Pervasive algebras on planar compacts

Jan Čerych (1999)

Commentationes Mathematicae Universitatis Carolinae

We characterize compact sets X in the Riemann sphere 𝕊 not separating 𝕊 for which the algebra A ( X ) of all functions continuous on 𝕊 and holomorphic on 𝕊 X , restricted to the set X , is pervasive on X .

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