Simulation of Effective Subshifts by Two-dimensional Subshifts of Finite Type

International audienceIn this article we study how a subshift can simulate another one, where the notion of simulation is given by operations on subshifts inspired by the dynamical systems theory (factor, projective subaction...). There exists a correspondence between the notion of simulation and the set of forbidden patterns. The main result of this paper states that any effective subshift of dimension d – that is a subshift whose set of forbidden patterns can be generated by a Turing machine – can be obtained by applying dynamical operations on a subshift of finite type of dimension d + 1 – a subshift that can be defined by a finite set of forbidden patterns. This result improves Hochman's [Hoc09]

1D Effectively Closed Subshifts and 2D Tilings

Michael Hochman showed that every 1D effectively closed subshift can be simulated by a 3D subshift of finite type and asked whether the same can be done in 2D. It turned out that the answer is positive and necessary tools were already developed in tilings theory. We discuss two alternative approaches: first, developed by N. Aubrun and M. Sablik, goes back to Leonid Levin; the second one, developed by the authors, goes back to Peter Gacs.Comment: Journ\'ees Automates Cellulaires, Turku : Finland (2010