Hybrid fixed point result for lipschitz homomorphisms on quasi-Banach algebras

We shall generalize the results of [9] about characterization of isomorphisms on quasi-Banach algebras by providing integral type conditions. Also, we shall give some new results in this way and finally, give a result about hybrid fixed point of two homomorphisms on quasi-Banach algebras.     

Finite fixed point algebras are subdiagonalisable

Presented by Joel Berman.     

Complex homomorphisms on self-conjugate algebras of functions

Let X be a non-void set and A be a subalgebra of \({\mathbb{C}^{X}}\) . We call a \({\mathbb{C}}\) -linear functional \({\varphi}\) on A a 1-evaluation if \({\varphi(f) \in f(X) }\) for all \({f\in A}\) . From the classical Gleason–Kahane–?elazko theorem, it follows that if X in addition is a compact Hausdorff space then a mapping \({\varphi}\) of \({C_{\mathbb{C}}(X) }\) into \({\mathbb{C}}\) is a 1-evaluation if and only if \({\varphi}\) is a \({\mathbb{C}}\) -homomorphism. In this paper, we aim to investigate the extent to which this equivalence between 1-evaluations and \({\mathbb{C}}\) -homomorphisms can be generalized to a wider class of self-conjugate subalgebras of \({\mathbb{C}^{X}}\) . In this regards, we prove that a \({\mathbb{C}}\) -linear functional on a self-conjugate subalgebra A of \({\mathbb{C}^{X}}\) is a positive \({\mathbb{C}}\) -homomorphism if and only if \({\varphi}\) is a \({\overline{1}}\) -evaluation, that is, \({\varphi(f) \in\overline{f\left(X\right)}}\) for all \({f\in A}\) . As consequences of our general study, we prove that 1-evaluations and \({\mathbb{C}}\) -homomorphisms on \({C_{\mathbb{C}}\left( X\right)}\) coincide for any topological space X and we get a new characterization of realcompact topological spaces.     

On symmetric algebras which are Cohen Macaulay

We give some necessary and sufficient conditions for S_A(m) being Cohen-Macaulay, where S_A(m) is the Symmetric algebra of the maximal ideal of an homomorphic image A of a regular local ring.This paper was supported by C.N.R. (Consiglio Nazionale delle Ricerche)     

Group algebras in which complements are summands

It is shown that (1) every almost self-injective group algebra is self-injective and (2) if the group algebra KG is continuous, then G is a locally finite group. Furthermore, it follows that the following assertions are equivalent: a CS group algebra KG is continuous; KG is principally self-injective; the group G is locally finite. __________ Translated from Fundamentalnaya i Prikladnaya Matematika, Vol. 11, No. 3, pp. 3–11, 2005.     

Algebra homomorphisms from cosine convolution algebras

In this paper we deal with the weighted Banach algebra L _ω ¹ (ℝ⁺, * _c ), where *_c is the cosine convolution product. We describe its character space and its multiplier algebra. Our main results concern bounded algebra homomorphisms from L _ω ¹ (ℝ⁺, * _c ). We give a variant of Kisyński’s theorem for such homomorphisms and characterize them in terms of integrated cosine functions. A generalized form of the Sova-Da Prato-Giusti theorem about generation of cosine functions is also given. Partly supported by Project MTM2004-03036 and MTM 2007-61446, DGI-FEDER, of the MCYT, Spain, and Project E-64, D. G. Aragón, Spain.     

A note on realizing homomorphisms of category algebras

The complete Boolean homomorphisms from the category algebra $\text{C}$(X) of a complete matrix space X to the category algebra $\text{C}$(Y) of a Baire topological space Y are characterized as those σ-homomorphisms which are induced by continuous maps from dense G₈-subsets of Y into X. This result is used to deduce a series of related results in topology and measure theory (some of which are well-known). Finally a similar result for the complete Boolean homomorphisms from the category algebra $\text{C}$(X) of a compact Hausdorff space X tothe category algebra $\text{C}$(Y) of a Baire topological space Y is proved.     

Endomorphisms and homomorphisms of Heyting algebras

For a non-trivial Heyting algebraH, the cardinality of its endomorphism monoid is always at least two. If it is exactly two thenH is called 0-endomorphism rigid. It is shown that there exists a proper class of non-isomorphic 0-endomorphism rigid Heyting algebras. This is a consequence of a more general result: the variety of Heyting algebras is 0-universal.The support of NSERC is gratefully acknowledged.Presented by J. Berman.     

Weakly compact homomorphisms of regular Banach algebras

Let A be a uniformly regular Ditkin algebra. It is shown that every weakly compact homomorphism of A into a Banach algebra is finite-dimensional.     

Hyers-Ulam-Rassias stability of homomorphisms in quasi-Banach algebras

In this paper, we prove the Hyers-Ulam-Rassias stability of homomorphisms in quasi-Banach algebras. This is applied to investigate isomorphisms between quasi-Banach algebras.     

On homomorphisms between products of median algebras

Homomorphisms of products of median algebras are studied with particular attention to the case when the codomain is a tree. In particular, we show that all mappings from a product \({\mathbf{A_1} \times\ldots\times {\mathbf{A}_{n}}}\) of median algebras to a median algebra \({\mathbf{B}}\) are essentially unary whenever the codomain \({\mathbf{B}}\) is a tree. In view of this result, we also characterize trees as median algebras and semilattices by relaxing the defining conditions of conservative median algebras.