4,457 research outputs found
Path sets in one-sided symbolic dynamics
Path sets are spaces of one-sided infinite symbol sequences associated to
pointed graphs (G_v_0), which are edge-labeled directed graphs G with a
distinguished vertex v_0. Such sets arise naturally as address labels in
geometric fractal constructions and in other contexts. The resulting set of
symbol sequences need not be closed under the one-sided shift. this paper
establishes basic properties of the structure and symbolic dynamics of path
sets, and shows they are a strict generalization of one-sided sofic shifts.Comment: 16 pages, 6 figures; v2, 22pages, 6 figures; title change, adds a new
Theorem 1.5, and a second Appendix, v3, 21 pages, revisions to exposition; v4
revised introduction; v5, 22 pages, changed title, revised introductio
On the Sets of Real Numbers Recognized by Finite Automata in Multiple Bases
This article studies the expressive power of finite automata recognizing sets
of real numbers encoded in positional notation. We consider Muller automata as
well as the restricted class of weak deterministic automata, used as symbolic
set representations in actual applications. In previous work, it has been
established that the sets of numbers that are recognizable by weak
deterministic automata in two bases that do not share the same set of prime
factors are exactly those that are definable in the first order additive theory
of real and integer numbers. This result extends Cobham's theorem, which
characterizes the sets of integer numbers that are recognizable by finite
automata in multiple bases.
In this article, we first generalize this result to multiplicatively
independent bases, which brings it closer to the original statement of Cobham's
theorem. Then, we study the sets of reals recognizable by Muller automata in
two bases. We show with a counterexample that, in this setting, Cobham's
theorem does not generalize to multiplicatively independent bases. Finally, we
prove that the sets of reals that are recognizable by Muller automata in two
bases that do not share the same set of prime factors are exactly those
definable in the first order additive theory of real and integer numbers. These
sets are thus also recognizable by weak deterministic automata. This result
leads to a precise characterization of the sets of real numbers that are
recognizable in multiple bases, and provides a theoretical justification to the
use of weak automata as symbolic representations of sets.Comment: 17 page
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