Then the neighbors of u 1 are mapped to v 2 and the neighbors of u 2 are mapped to v 1 . Because v 2 has no neighbors, there are no mappings to u 3 . The nodes u 4 and u 5 can map to H in two different ways, and the mapping with the largest overlap is (u 3 , u 4 , u 5 ) → ( * , v 5 , v 4 ) where * is a placeholder for no mapping. The outcome of the placeholder will depend on which mapping function is used, either T, T † , or T ‡ . Lastly, only H has nodes at a depth of 2, and so the process has completed and the mapping is