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Remarks on some fundamental results about higher-rank graphs and their C*-algebras

Published online by Cambridge University Press:  30 April 2013

Robert Hazlewood
School of Mathematics and Statistics, University of New South Wales, Sydney, NSW 2052, Australia (
Iain Raeburn
Department of Mathematics and Statistics, University of Otago, PO Box 56, Dunedin 9054, New Zealand (
Aidan Sims
School of Mathematics and Applied Statistics, University of Wollongong, NSW 2522, Australia (;
Samuel B. G. Webster
School of Mathematics and Applied Statistics, University of Wollongong, NSW 2522, Australia (;
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Results of Fowler and Sims show that every k-graph is completely determined by its k-coloured skeleton and collection of commuting squares. Here we give an explicit description of the k-graph associated with a given skeleton and collection of squares and show that two k-graphs are isomorphic if and only if there is an isomorphism of their skeletons which preserves commuting squares. We use this to prove directly that each k-graph Λ is isomorphic to the quotient of the path category of its skeleton by the equivalence relation determined by the commuting squares, and show that this extends to a homeomorphism of infinite-path spaces when the k-graph is row finite with no sources. We conclude with a short direct proof of the characterization, originally due to Robertson and Sims, of simplicity of the C*-algebra of a row-finite k-graph with no sources.

Research Article
Copyright © Edinburgh Mathematical Society 2013


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