Example of the reduction from tree edit distance to maximum clique. We consider the case of γ(a, ∈) = γ(∈, a) = 1, γ(a, a) = 0, and γ(a, b) = 2 for a ≠ b (i.e., f(v, v) = 2 and f(u, v) = 0 for ℓ(u) ≠ ℓ(v)). In the left figure, both label and node ID are shown above and below parts of each node, respectively. Vertices with f(u
) = 0 are omitted in the right figure. The maximum clique shown by bold lines in the right figure corresponds to the optimal edit distance mapping shown by broken lines in the left figure.