

Algebras in Analysis
November 29, 2019 18:05–19:35, Moscow, Lomonosov Moscow State University, room 1320.






Metrics on doubles as an inverse semigroup
V. M. Manuilov^{} 
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Abstract:
For a metric space $X$ we study metrics on the two copies of $X$. We define composition of such metrics and show that the equivalence classes of metrics are a semigroup $M(X)$. Our main result is that $M(X)$ is an inverse semigroup, therefore, one can define the $C^*$algebra of this inverse semigroup. This new $C^*$algebra of a metric space is not necessarily commutative and differs from the Roe algåbra. If the Gromov–Hausdorff distance between two metric spaces, $X$ and $Y$, is finite then their inverse semigroups $M(X)$ and $M(Y)$ (and hence their $C^*$algebras) are isomorphic. We characterize the metrics that are idempotents, and give examples of metric spaces, for which the semigroup $M(X)$ (and the corresponding $C^*$algebra) is commutative. We also describe the class of metrics determined by subsets of $X$ in terms of the closures of the subsets in the Higson corona of $X$ and the class of invertible metrics.

