Non Expansive Directions for Z Actions
نویسندگان
چکیده
We show that any direction in the plane occurs as the unique nonexpansive direction of a Z2 action, answering a question of Boyle and Lind. In the case of rational directions, the subaction obtained is non-trivial. We also establish that a cellular automaton acting on a subshift can have zero Lyapunov exponents and at the same time act sensitively; and more generally, for any positive real θ there is a cellular automaton acting on an appropriate subshift with λ+ = −λ− = θ.
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