  It is well-known that the spacetime diagrams of some cellular automata have a
fractal structure: for instance Pascal's triangle modulo 2 generates a
Sierpinski triangle. Explaining the fractal structure of the spacetime diagrams
of cellular automata is a much explored topic, but virtually all of the results
revolve around a special class of automata, whose typical features include
irreversibility, an alphabet with a ring structure, a global evolution that is
a ring homomorphism, and a property known as (weakly) p-Fermat. The class of
automata that we study in this article has none of these properties. Their cell
structure is weaker, as it does not come with a multiplication, and they are
far from being p-Fermat, even weakly. However, they do produce fractal
spacetime diagrams, and we explain why and how.
