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An AF Algebra Associated with the Farey Tessellation

Published online by Cambridge University Press:  20 November 2018

Florin P. Boca*
Affiliation:
Department of Mathematics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, U.S.A. Institute of Mathematics “Simion Stoilow” of the Romanian Academy, P.O. Box 1-764, RO-014700 Bucharest, Romania e-mail:fboca@math.uiuc.edu
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Abstract

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We associate with the Farey tessellation of the upper half-plane an $\text{AF}$ algebra $\mathfrak{A}$ encoding the “cutting sequences” that define vertical geodesics. The Effros–Shen $\text{AF}$ algebras arise as quotients of $\mathfrak{A}$. Using the path algebra model for $\text{AF}$ algebras we construct, for each $\tau \,\,\in \,\,\left( 0 \right.,\left. \frac{1}{4} \right]$, projections $({{E}_{n}})$ in $\mathfrak{A}$ such that ${{E}_{n}}{{E}_{n\pm 1}}E\le \tau {{E}_{n}}$.

Type
Research Article
Copyright
Copyright © Canadian Mathematical Society 2008

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