Of the 263 invalid OCL SMILES, 237 were the already known problematic aromatic selenium compounds within a non-aromatic SMILES, 25 had problems with the assignment of aromatic bonds, while one SMILES contained an incorrect nitrogen notation "[N-13]". Again, it is interesting to note that the results from OCL and CDK are very close to each other. The invalid RDKit SMILES were too numerous for (detailed) further inspection, but are available in the supplementary material . and such searches can take quite some time, depending on the query structure. Thus, to achieve reasonable search results in a short time, the number of ABAS searches needs to be reduced to a minimum, which is achieved by a fast fingerprint compound pre-selection step. Thus, fingerprints should deliver a superset of compound candidates, which are then narrowed down by ABAS to the set of compounds that truly contain that substructure. The smaller the difference between this initial fingerprint list and the number of final compounds, the better and thus the more efficient the applied fingerprint algorithm. As a consequence, many fingerprint algorithms have been developed and optimized for pre-selection.