  If the no-signalling principle was the only limit to the strength of
non-local correlations, we would expect that any form of no-signalling
correlation can indeed be realized. That is, there exists a state and
measurements that remote parties can implement to obtain any such correlation.
Here, we show that in any theory in which some functions cannot be computed,
there must be further limits to non-local correlations than the no-signalling
principle alone. We proceed to argue that even in a theory such as quantum
mechanics in which non-local correlations are already weaker, the question of
computability imposes such limits.
