 If \(\mathcal{A}\) is a test space, an \(\mathcal{A}\)-event is a set of \(\mathcal{A}\)-outcomes that is contained in some test. In other words, an \(\mathcal{A}\)-event is simply an event in the classical sense for any one of the tests belonging to \(\mathcal{A}\). Now, if \(A\) and \(B\) are two \(\mathcal{A}\)-events, we say that \(A\) and \(B\) are orthogonal, and write \(A\binbot B\), if they are disjoint and their union is again an event. We say that two orthogonal events are complements of one another if their union is a test. We say that events \(A\) and \(B\) are perspective, and write \(A\sim B\), if they share any common complement. (Notice that any two tests \(E\) and \(F\) are perspective, since they are both complementary to the empty event.)