Finite automata for Schreier graphs of virtually free groups
  The Stallings construction for finitely generated subgroups of free groups is generalized by introducing the concept of Stallings section, which allows an eficient computation of the core of a Schreier graph based on edge folding. It is proved that those groups admitting Stallings sections are precisely finitely generated virtually free groups, through a constructive approach based on Bass-Serre theory. Complexity issues and applications are also discussed. 
Pedro Silva, Xaro Soler-Escriv\`a, Enric Ventura
math.GR