Non-expansive directions for ℤ<sup>2</sup> actions
Non-expansive directions for ℤ<sup>2</sup> actions
Abstract We show that any direction in the plane occurs as the unique non-expansive direction of a ℤ 2 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 …