The edit path may involve three types of operations, node insertion, node deletion, and node substitution, each associated with a specific 'cost.' The GED is a graph arithmetic operation analogous to the Levenshtein distance between strings , and it does not take into direct consideration the chemical information, which however is essential when comparing synthetic routes. Genheden et al. introduced chemical information in the GED by enabling the GED cost functions to include calculations of chemical similarity at molecular and reaction levels.