Constructing the PLA (2/2)
For each member in A(k - 1), say (x, k - 1), we consider in the k-th step all vertices of the form (x’, k), where x’ is either x or a nearest neighbor of x.
If (x’, k) is an NR vertex, it is added to the set A(x).
The serach is terminated when either k = τ + 1, of the set A(k) is empty.