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We use homotopy theoretic ideas to study the $K$-theory of (graded, Real) $C^*$-algebras in detail. After laying the foundations, and deriving the formal properties, the comparison of the model with the Kasparov picture of $K$-theory has…

K-Theory and Homology · Mathematics 2024-10-30 Anupam Datta

In this paper we introduce an abstract approach to higher order smooth systems on $C^*$-algebras in contest of Baaj-Julg picture of $\KK$-theory.

K-Theory and Homology · Mathematics 2011-03-24 Nikolay P. Ivankov

We show that the K-theory of C*-algebras can be defined by pairs of matrices satisfying less strict relations than idempotency.

Operator Algebras · Mathematics 2013-04-10 Vladimir Manuilov

We introduce two new model comparison games that characterize separability by first-order formulas with generalized quantifiers. One is built on the Ehrenfeucht-Fra\"iss\'e game and the other is a formula-size game.

Logic · Mathematics 2026-05-21 Antti Kuusisto , Miguel Moreno , Matias Selin

This paper argues that the unitary Cuntz semigroup, introduced in [10] and termed Cu$_1$, contains crucial information regarding the classification of non-simple C$^*$-algebras. We exhibit two (non-simple) C$^*$-algebras that agree on their…

Operator Algebras · Mathematics 2022-10-25 Laurent Cantier

We establish several strong equivalences of synchronous non-local games, in the sense that the corresponding game algebras are $*$-isomorphic. We first show that the game algebra of any synchronous game on $n$ inputs and $k$ outputs is…

Quantum Physics · Physics 2021-09-13 Samuel J. Harris

Let $A$ be a unital $C^*$-algebra. Its unitary group, $UA$, contains a wealth of topological information about $A$. However, the homotopy type of $UA$ is out of reach even for $A = M_2(\CC)$. There are two simplifications which have been…

Operator Algebras · Mathematics 2009-09-22 John R. Klein , Claude L. Schochet , Samuel B. Smith

We define the categorical cohomology of a k-graph \Lambda\ and show that the first three terms in this cohomology are isomorphic to the corresponding terms in the cohomology defined in our previous paper. This leads to an alternative…

Operator Algebras · Mathematics 2013-08-15 Alex Kumjian , David Pask , Aidan Sims

For two unital Kirchberg algebras with finitely generated K-groups, we introduce a property, called reciprocality, which is proved to be closely related to the homotopy theory of Kirchberg algebras. We show the Spanier--Whitehead duality…

Operator Algebras · Mathematics 2022-08-30 Taro Sogabe

We show that certain extensions of classifiable C*-algebra are strongly classified by the associated six-term exact sequence in K-theory together with the positive cone of K_{0}-groups of the ideal and quotient. We apply our result to give…

Operator Algebras · Mathematics 2013-02-01 Soren Eilers , Gunnar Restorff , Efren Ruiz

In this work we construct a C*-algebra from an injective endomorphisms of some group G, allowing the endomorphism to have infinite cokernel. We generalize results obtained by I. Hirshberg and also by J. Cuntz and A. Vershik. In good cases…

Functional Analysis · Mathematics 2018-03-13 Felipe Vieira

Let $\mathcal{B}$ be a nonunital separable simple stable C*-algebra with strict comparison of positive elements and $T(\mathcal{B})$ having finite extreme boundary, and let $\mathcal{A}$ be a simple unital separable nuclear C*-algebra. We…

Operator Algebras · Mathematics 2022-12-20 Jireh Loreaux , P. W. Ng , Arindam Sutradhar

We introduce the category of optiongraphs and option-preserving maps as a model to study impartial combinatorial games. Outcomes, remoteness, and extended nim-values are preserved under option-preserving maps. We show that the four…

Combinatorics · Mathematics 2025-10-23 Mikhail Baltushkin , Dana C. Ernst , Nándor Sieben

We classify all essential extensions of the form $$0 \rightarrow \W \rightarrow \D \rightarrow A \rightarrow 0$$ where $\W$ is the unique separable simple C*-algebra with a unique tracial state, with finite nuclear dimension and with…

Operator Algebras · Mathematics 2020-06-02 Huaxin Lin , Ping Wong Ng

Connectivity is a homotopy invariant property of separable C*-algebras which has three notable consequences: absence of nontrivial projections, quasidiagonality and a more geometric realization of KK-theory for nuclear C*-algebras using…

Operator Algebras · Mathematics 2019-10-03 Marius Dadarlat , Ulrich Pennig

Motivated by classical facts concerning closed manifolds, we introduce a strong finiteness property in K-homology. We say that a C*-algebra has uniformly summable K-homology if all its K-homology classes can be represented by Fredholm…

Operator Algebras · Mathematics 2015-12-16 Heath Emerson , Bogdan Nica

We study the Cuntz semigroup for non-simple $\text{C}^*$-algebras in this paper. In particular, we use the extended Elliott invariant to characterize the Cuntz comparison for $\text{C}^*$-algebras with the projection property which have…

Operator Algebras · Mathematics 2017-09-15 George Elliott , Kun Wang

We prove simplicity and pure infiniteness results for a certain class of labelled graph $C^*$-algebras. We show, by example, that this class of unital labelled graph $C^*$-algebras is strictly larger than the class of unital graph…

Operator Algebras · Mathematics 2008-01-15 T. Bates , D. A. Pask

Multiplicative Unitaries are described in terms of a pair of commuting shifts of relative depth two. They can be generated from ambidextrous Hilbert spaces in a tensor C*-category. The algebraic analogue of the Takesaki-Tatsuuma Duality…

Operator Algebras · Mathematics 2007-05-23 S. Doplicher , C. Pinzari , J. E. Roberts

We introduce the notion of admissible injective envelope for a locally C*-algebra and show that each object in the category whose objects are unital Fr\'{e}chet locally C*-algebras and whose morphisms are unital admissible local completely…

Operator Algebras · Mathematics 2026-02-04 Maria Joiţa , Gheorghe-Ionuţ Şimon
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