Running Tree Automata on Trees and/or Dags
Résumé
We define tree/dag automata as extensions of (unranked) tree automata which can run indifferently on trees or dags, in a bottom-up style. The runs of such an automaton A on any tree or dag t are defined by assigning states not only to the nodes of t, but also to its edges. Runs are so defined that A accepts t if and only if it accepts the tree \hat{t} obtained by unfolding t, as a tree automaton running in the usual sense on \hat{t}.