As before, we calculate the joint probability for disynthons by calculating the number of entries in S, N , and then we apply eq 2. Moreover, we also identify certain combinations of clusters that are not observed in the experimental data (Figure ). While the analysis does not indicate why these combinations of building blocks are not observed, we believe characterizing these gaps could be useful. For example, gaps could be new combinations of building blocks that might be desirable to test. On the other hand, these gaps could also indicate that the combination cannot not be made (e.g. due to a DEL being formed using several different reactions, so that certain building blocks cannot be crosslinked given the reactions employed) or that something went wrong experimentally so that even though the combination was thought to be tested, no data was collected. Thus, in some cases, gaps in the data may represent building blocks or combinations of building blocks to avoid and in others, areas to test in further rounds of experimentation.