The reason behind the rejection was the presence of a non-resolvable cycle in a given synthesis route candidate. The SynGPS algorithm correctly rejects such routes, as a viable synthesis route must be a directed acyclic graph (DAG) in the context of this algorithm. So that question arises: How is it possible that the extension of synthesis routes will introduce non-resolvable cycles? To answer this question, we illustrate the situation via one example of the rejected routes, shown in Figure . The viability of a synthesis route candidate revolves around two major aspects: the lack of cycles and the inventory status of the involved substances. Due to the lack of real inventory information, it needed to be made up for meaningful benchmarking, as described in section "AICP Inventory Generation". For the sake of simplicity, let's assume that all substance nodes that are leaf nodes (i.e. have no parent node) are available from inventory, thus could be used as starting materials.