We also investigated how many of the similar compounds we could retrieve in a chemical series extracted from the literature. With a beam search of 10,000, it was found that approximately 87% of the similar compounds could be retrieved. Reasons that a similar compound could not be retrieved is due to that beam search is an approximation of an exhaustive search or that the transformation from a source compound to a target compound have low precedence, i.e. the transformation is now well represented in the training set. This might happen for uncommon chemical substructures. Low precedence have been discussed in the context of modifying an atom in penicillin.