The closest chemical equivalent to the Shakespeare example described in the previous section is locating a predefined molecule in chemical space, i.e. rediscovery. Brown et al. have demonstrated this for three drug molecules: celecoxib, troglitazone, and tiotixene (Figure ). Here similarity to the target is measured by the Tanimoto similarity, which is computed by decomposing each molecule into overlapping fragments up to a certain size and then counting how many fragments the two molecules have in common and dividing by the combined total number of fragments. Thus, the Tanimoto score ranges from 0 (no similarity) to 1 (very similar or identical).