Séminaire de Géométrie, Groupes et Dynamique

Ville Salo: "Universal groups of cellular automata"

Europe/Paris
435 (UMPA)

435

UMPA

Description
The full shift is the topological dynamical system of bi-infinite sequences over a finite alphabet under
the shift map. Its automorphism group, the group of (reversible) cellular automata, has a rich family of
finitely-generated subgroups, including all finite, f.g. abelian and f.g. free groups, and several groups
with undecidable torsion problem. Many closure properties are also known for this family, such as
closure under direct products and free products. The group itself is not finitely-generated.
Nevertheless, we show that there is a finitely-generated subgroup that is universal, in the sense that it
contains an embedded copy of every other finitely-generated subgroup.