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Discrete Dynamics in Nature and Society
Volume 2012, Article ID 818549, 15 pages
Research Article

Substitutions with Vanishing Rotationally Invariant First Cohomology

Facultad de Ciencias Matemรกticas y Fรญsicas, Universidad de Oviedo, 33007 Oviedo, Spain

Received 17 November 2011; Accepted 5 December 2011

Academic Editor: Bo Yang

Copyright © 2012 Juan García Escudero. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The cohomology groups of tiling spaces with three-fold and nine-fold symmetries are obtained. The substitution tilings are characterized by the fact that they have vanishing first cohomology group in the space of tilings modulo a rotation. The rank of the rational first cohomology, in the tiling space formed by the closure of a translational orbit, equals the Euler totient function evaluated at ๐‘ if the underlying rotation group is ๐™ ๐‘ . When the symmetries are of crystallographic type, the cohomologies are infinitely generated.