Not all problems in quantum information can be simply and immediately mapped in a useful way onto a single framework, and those that cannot are what make quantum information an interesting, as well as a rather difficult, field of research. Note that the single framework rule forbids combining incompatible frameworks, but allows one to compare them or work out relationships that hold between results in different frameworks. Therefore one can say that, at least in some general sense, problems at the frontiers of quantum information theory have to do with comparisons of incompatible frameworks. See the   Further Reading supplement for additional discussions of these issues. Griffiths (2013).--> 