Tilings and associated relational structures
In the present paper, as we did previously in [7], we investigate the relations between the geometric properties of tilings and the algebraic properties of associated relational structures. Our study is motivated by the existence of aperiodic tiling systems. In [7], we considered tilings of the euclidean spaces of finite dimension, and isomorphism was defined up to translation. Here, we consider, more generally, tilings of a metric space, and isomorphism is defined modulo an arbitrary group of isometries. In Section 1, we define the relational structures associated to tilings. The results of Section 2 concern local isomorphism, the extraction preorder and the characterization of relational structures which can be represented by tilings of some given type. In Section 3, we show that the notions of periodicity and invariance through a translation, defined for tilings of the euclidean spaces of finite dimension, can be generalized, with appropriate hypotheses, to relational structures, and in particular to tilings of noneuclidean spaces. The results of Section 4 are valid for uniformly locally finite relational structures, and in particular tilings, which satisfy the local isomorphism property. We characterize among such structures those which are locally isomorphic to structures without nontrivial automorphism. We show that, in an euclidean space of finite dimension, this property is true for a tiling which satisfies the local isomorphism property if and only if it is not invariant through a nontrivial translation. We illustrate these results with examples, some of them concerning aperiodic tilings systems of euclidean or noneuclidean spaces.