On Algebraic Structure of Neighborhoods of Cellular Automata-Horse Power Problem-

In a previous paper we formulated and analyzed the structure of neighborhoods of cellular automata in an algebraic setting such that the cellular space S is represented by the Cayley graph of a finitely generated group and the neighbors are defined as a semigroup generated by the neighborhood N as a subset of S, Nishio and Margenstern 2004 [14,15]. Particularly we discussed the horse power problem whether the motion of a horse (knight) fills the infinite chess board or Z^2- that is, an algebraic problem whether a subset of a group generates it or not. Among others we proved that a horse fills Z^2 even when its move is restricted to properly chosen 3 directions and gave a necessary and sufficient condition for a generalized 3-horse to fill Z^2. This paper gives further developments of the horse power problem, say, on the higher dimensional Euclidean grid, the hexagonal grid and the hyperbolic plane.