 Suppose that darts are shot at a dart board using an indeterministic process that can hit any part of the board. (If the reader is not comfortable with indeterministic darts, she may imagine photons hitting a scintillation screen after passing through a narrow slit.) Suppose that A and B are two regions of the dart board such that A is fully contained within B, and B does not fill the entire board (see  Figure 5(a)).  Let A be the event corresponding to the dart landing in region A, and analogously for B. Then we will have: