Constructing the PLA (1/2)
Use a BFS on the mobility graph, beginning from the vertex (X0, 0).
The BFS is conducted in steps, where the k-th step accepts as an input a set, A(k - 1), produced by the (k - 1) step, and generates the set A(k).
A(k) is the set of NR vertices of the form (x, k), connected to the vertex (X0, 0) through a feasible roaming path.