Composite Systems

If we are interested in two completely separate systems, then the set of questions we can ask includes anything we can ask about either of them as well as the logical conjunctions and disjunctions of such questions. For example if each of them is a simple spin 1/2 particle we can ask whether the first is up AND the second down, or [[can check whether they are parallel by asking]] whether we have ((first up)AND(second up))OR((first down)AND(second down)).