 B1 and B3 together entail B4. Assuming B1 and B4, B2 is equivalent to B3. Notice that if it is assumed that every world contains at least one fact (a principle we shall call ‘Plenitude’), then B3 implies B4 (take \(G = F)\). Also notice that both B1 and B4 entail Plenitude. See Figure 1.