Über den Satz von Wiener und Lokalkompakte Gruppen
Über ein Problem von Reiter und ein Problem von Derighetti zur Eigenschaft P... lokalkompakter Gruppen
Umbral calculus and cancellative semigroup algebras.
Une preuve rapide du théorème de Beurling et Helson sur les endomorphismes de l'algèbre l¹(Z)
Uniformly continuous functionals on Banach algebras
Uniqueness of rotation invariant norms.
Uniqueness of the topology on L¹(G)
Let G be a locally compact abelian group and let X be a translation invariant linear subspace of L¹(G). If G is noncompact, then there is at most one Banach space topology on X that makes translations on X continuous. In fact, the Banach space topology on X is determined just by a single nontrivial translation in the case where the dual group Ĝ is connected. For G compact we show that the problem of determining a Banach space topology on X by considering translation operators on X is closely related...
Unitary Banach algebras
In a Banach algebra an invertible element which has norm one and whose inverse has norm one is called unitary. The algebra is unitary if the closed convex hull of the unitary elements is the closed unit ball. The main examples are the C*-algebras and the ℓ₁ group algebra of a group. In this paper, different characterizations of unitary algebras are obtained in terms of numerical ranges, dentability and holomorphy. In the process some new characterizations of C*-algebras are given.