Higher P(active) in individual positions leads to higher probability of molecule activity. To understand how varying the P(active) values of building blocks at each position affects the probability of forming an active trisynthon, we calculate joint probabilities for pairs of building block positions, using the P(active) bins shown in Figure . We refer to bin positions numerically, where 1 is the lowest bin of P(active) values, [0.00, 0.20), and 4 is the highest bin of P(active) values, [0.80, 1.00]. The subset of compounds where the building block in p i is a member of bin x (denoted by the set membership symbol ∈) and the building block in p j is a member of bin y is