In summary, at least in the case of drug-like molecules it is possible to locate specific molecules in chemical space by evaluating a relatively small subset ). Similarly to the Shakespeare example, the reason is that many of the molecules in chemical space have some structural motifs in common with the target molecule. Search algorithms like GAs can then combine these structural motifs to create molecules that are increasingly similar to the target molecules. The order in which these fragments are combined correspond to different (interconnected) paths in chemical space that all lead to the target molecules (Figure ). There are a vast number of such paths, so it is highly likely to randomly encounter at least one such path, which can then be followed to the target. In this particular case, the search is frustrated by the use of the Tanimoto similarity as the scoring function, since it is only a semi-continuous function (cf. Figure ) of the molecular structure in the sense that all atoms and bonds in a fragment must be placed correctly before the fragment is counted as found.