As shown in the work of Zahoránszky-Kőhalmi et al. , viable synthesis routes can be uniquely represented by the node identifiers provided that each node identifier is unique across both node types, that is substance and reaction nodes. This is, however, typically the case, as the identifier of substances and reactions are their InChI-Keys and reaction IDs (rxids), respectively. Therefore, if the representation of synthesis routes based on the node identifiers is identical, then the two synthesis routes must be identical. Therefore, if two viable synthesis routes have an overlapping set of node identifiers, then one route can be thought of the extension of the other one (setting aside the inventory status of the substances). Of note, if two viable synthesis routes are overlapping solely by the target molecule, then none of them is considered as the extended synthesis route of the other. In fact, it is easy to see that the routes represent two different viable synthesis routes.