Multiplicative functionals and entire functions
Let A be a complex Banach algebra with a unit e, let T, φ be continuous functionals, where T is linear, and let F be a nonlinear entire function. If T ∘ F = F ∘ φ and T(e) = 1 then T is multiplicative.
Multiplicative functionals and entire functions, II
Let A be a complex Banach algebra with a unit e, let F be a nonconstant entire function, and let T be a linear functional with T(e)=1 and such that T∘F: A → ℂ is nonsurjective. Then T is multiplicative.
Almost multiplicative functionals
A linear functional F on a Banach algebra A is almost multiplicative if |F(ab) - F(a)F(b)| ≤ δ∥a∥ · ∥b∥ for a,b ∈ A, for a small constant δ. An algebra is called functionally stable or f-stable if any almost multiplicative functional is close to a multiplicative one. The question whether an algebra is f-stable can be interpreted as a question whether A lacks an almost corona, that is, a set of almost multiplicative functionals far from the set of multiplicative functionals. In this paper we discuss...
A generalization of the Banach-Stone theorem
Multipliers in complex Banach spaces and structure of the unit balls
Wiesław Żelazko, topological algebras, Banach algebras
Riemann mapping theorem in ℂⁿ
The classical Riemann Mapping Theorem states that a nontrivial simply connected domain Ω in ℂ is holomorphically homeomorphic to the open unit disc 𝔻. We also know that "similar" one-dimensional Riemann surfaces are "almost" holomorphically equivalent. We discuss the same problem concerning "similar" domains in ℂⁿ in an attempt to find a multidimensional quantitative version of the Riemann Mapping Theorem
Small deformations of topological algebras
We investigate stability of various classes of topological algebras and individual algebras under small deformations of multiplication.
Automatic continuity of biseparating maps
We prove that a biseparating map between spaces of vector-valued continuous functions is usually automatically continuous. However, we also discuss special cases when this is not true.
Noncommutative uniform algebras
We show that a real Banach algebra A such that ||a²|| = ||a||² for a ∈ A is a subalgebra of the algebra of continuous quaternion-valued functions on a compact set X.
Topological algebras in which all maximal two-sided ideals are closed
We characterize unital topological algebras in which all maximal two-sided ideals are closed.
A function algebra without any point derivation
A discontinuous function does not operate on the real part of a function algebra
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