On the other hand, as we show in this paper, possibilities for measurement in box world are in some ways rather limited. It turns out that there is nothing analogous to a Bell measurement. We also show that there is no entanglement swapping, teleportation, or dense coding. This extends to the whole of box world previous special-case results in [@barrett; @coupler].

As entanglement swapping is possible in the quantum world [@swapping], it follows that box world does not contain quantum theory as a special case, and that it cannot be the true theory describing reality.

A framework for probabilistic theories
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In order to compare classical theories, quantum theories, and alternatives such as box world, we need a common mathematical framework in which the different theories can be written down. We begin by describing such a framework. It is operational in flavour. This means, for example, that *system*, *preparation* and *measurement* are all taken as basic terms. Different ways of preparing a system will prepare different *states*. The state of a system determines the outcome probabilities for any measurement that can be performed on the system. The framework we describe and the notation we use is closely based on that 