Consider two logically unrelated propositions \(H\) and \(X\). Now consider the four “state descriptions” of this simple model as set out in Figure 1. So \(a=H\cap X\) and so on. Now define \(Y=a \cup d\). Alternatively, consider three propositions related in the following way: \(Y\) is defined as “\(H\) if and only if \(X\)”.