On a characterization of cellular automata in tilings of the hyperbolic plane

In this paper, we look at the extention of Hedlund's characterization of cellular automata to the case of cellular automata in the hyperbolic plane. This requires an additionnal condition. The new theorem is proved with full details in the case of the pentagrid and in the case of the ternary heptagrid and enough indications to show that it holds also on the grids $\{p,q\}$ of the hyperbolic plane.