Fig. 3

Weisfeiler-Lehman (WL) relabeling. Two iterations of Weisfeiler-Lehman vertex relabeling for a graph with discrete labels in {A,B}. At initialization (left), vertex labels are left in their original state. In the first iteration (middle), a new label is computed for each vertex, determined by the unique combination of its own and its neighbors’ labels. For example, the top-left vertex with label B has neighbors with labels A and B. This combination is renamed D and assigned to the top-left vertex in the first iteration. The second iteration (right) proceeds analogously