Lemma 1 A string w ∈ Σ* is accepted by an LTk automaton iff w is the concatenation of the symbols labeling the edges of a path through the LTk transition graph of A from h?, ∅i to an accepting node.
This is quick to verify. The path corresponding to any string w leads to a node labeled with hv, Si iff S = Fk(? w) and that will be a node that is circled iff augmented strings with that set of k-factors (plus v?) satisfy φA. There are a few important things to note about LTk transition graphs. First of all, every LTk automata over a given alphabet shares exactly the same node set and edge set. The only distinction between them is which nodes are accepting nodes and which are not. Secondly, they are invariably inconveniently large. Every LT2 automaton over a two symbol alphabet- pretty much the minimum interesting automaton-will have a transition graph the size of the graph of Figure 1. Fortunately, other than the graph of the example we will not have any need to draw these out. We can reason about the paths through them without ever actually looking at the entire graph.