2.1.3. Building block productivity increases the variety of active disynthon pairs. Having identified productive building blocks at each position, we proceed to investigate what characterizes a high P(active) building block chemically. To do so, we analyze how building blocks combine at a disynthon (pairwise) level. We hypothesize that building blocks with high P(active) values are compatible with a greater number of other building blocks. Here, we define two building blocks as compatible if they co-occur in an active compound.