Transformations of the one-dimensional cellular automata rule space

We introduce the notion of double permutation in order to study particular classes of transformations of the one-dimensional cellular automata rule space. These classes of transformations are characterized according to different sets of metrical, language theoretic, and dynamical properties they preserve. Each set of transformations we propose induces an equivalence relation over the cellular automata rule space. We give exact results on the cardinality of the quotient sets generated by these equivalence relations. Finally, we discuss some interesting open problems. © 1997 Elsevier Science B.V.