Fig. 1.

AiZynthFinder search tree nodes classification. Nodes are classified as: internal (I), solved (S), and not solved (NS). Internal nodes have a non-empty list of expandable molecules, but their depth is below a predefined depth. Solved nodes are leaves with all molecules in the in-stock list. A leaf marked as not solved means that it contains at least one expandable molecule and its depth exceeds a predefined threshold. Because we aim to discriminate promising nodes from non-promising ones as early as possible, we define a not solved node as all nodes that have no path to a solved leaf. In the majority of cases, we focus on roots of subtrees of not solved nodes