Given a unital ring R and a two-sided ideal I of R, we consider the question of determining when a unit of R/I can be lifted to a unit of R. For the wide class of separative exchange ideals I, we show that the only obstruction to lifting invertibles relies on a K-theoretic condition on I. This allows to extend previously known index theories to this context. Using this we can draw consequences ...

Let R be a unital semi-simple commutative complex Banach algebra, and let M(R) denote its maximal ideal space, equipped with the Gelfand topology. Sufficient topological conditions are given on M(R) for R to be a projective free ring, that is, a ring in which every finitely generated projective R-module is free. Several examples are included, notably the Hardy algebra H∞(X) of bounded holomorph...

We prove a Corona type theorem with bounds for the Sarason algebra H∞ + C and determine its spectral characteristics, thus continuing a line of research initiated by N. Nikolski. We also determine the Bass, the dense, and the topological stable ranks of H∞ + C. To fix our setting, let A be a commutative unital Banach algebra with unit e and M(A) its maximal ideal space. The following concept of...

The aim of this notes is to provide basic information about commutative Banach algebras. The final goal is to show that a unital, commutative complex Banach algebra A can be embedded as subalgebra of C(MA), the algebra of continuous functions on a w∗-compact setMA, known as the maximal ideal space or character space. Also, the non unital commutative complex Banach algebra can be embedded as a s...

The corona algebra M(A)/A contains essential information on the global structure of A, as demonstrated for instance by Busby theory. It is an interesting and surprisingly difficult task to determine the ideal structure of M(A)/A by means of the internal structure of A. Toward this end, we generalize Freudenthal’s classical theory of ends of topological spaces to a large class of C∗-algebras. Ho...

For each unital $C^*$-algebra $A$, we denote $cel_{CU}(A)=\sup\{cel(u):u\in CU(A)\}$, where $cel(u)$ is the exponential length of $u$ and $CU(A)$ closure commutator subgroup $U_0(A)$. In this paper, prove that $cel_{CU}(A)=2\pi$ provided $A$ an $AH$ algebras with slow dimension growth whose real rank not zero. On other hand, $cel_{CU}(A)\leq 2\pi$ when algebra ideal property no (if further assu...

In this paper, we investigate homomorphisms from unital C∗−algebras to unital Banach algebras and derivations from unital C∗−algebras to Banach A−modules related to a Cauchy–Jensen functional inequality. Mathematics subject classification (2010): 39B72, 46H30, 46B06.

In this brief note we would like to give the construction of a free commutative unital associative Nijenhuis algebra on a commutative unital associative algebra based on an augmented modified quasi-shuffle product. —————————————