Topological properties of cellular automata on trees
  We prove that there do not exist positively expansive cellular automata defined on the full k-ary tree shift (for k>=2). Moreover, we investigate some topological properties of these automata and their relationships, namely permutivity, surjectivity, preinjectivity, right-closingness and openness. 
Gabriele Fici (Universit\'e Nice Sophia Antipolis, France), Francesca   Fiorenzi (Universit\'e Paris-Sud 11, France)
cs.FL cs.CC cs.DM nlin.CG