  There are Hermitian operators on the tensor product \(H_1 \otimes H_2\) of a pair of Hilbert spaces \(H_1\) and \(H_2\) ... In the event that \(H_1\) and \(H_2\) are the state spaces of systems \(S1\) and \(S2\), \(H_1 \otimes H_2\) is the state-space of the complex system \((S1+S2)\). It follows from this by (4.1) that there are observables pertaining to \((S1+S2)\) whose values are not determined by the values of observables pertaining to the two individually.