Paper detail

An analogue of Cobham's theorem for graph directed iterated function systems

Feng and Wang showed that two homogeneous iterated function systems in $\mathbb{R}$ with multiplicatively independent contraction ratios necessarily have different attractors. In this paper, we extend this result to graph directed iterated function systems in $\mathbb{R}^n$ with contraction ratios that are of the form $\frac{1}β$, for integers $β$. By using a result of Boigelot et al., this allows us to give a proof of a conjecture of Adamczewski and Bell. In doing so, we link the graph directed iterated function systems to Büchi automata. In particular, this link extends to real numbers $β$. We introduce a logical formalism that permits to characterize sets of $\mathbb{R}^n$ whose representations in base $β$ are recognized by some Büchi automata. This result depends on the algebraic properties of the base: $β$ being a Pisot or a Parry number. The main motivation of this work is to draw a general picture representing the different frameworks where an analogue of Cobham's theorem is known.