 Here is one attempt. (Dickson 2004 analyzes some of the modal principles involved and suggests one line of argument, which he criticizes. Hooker 1972 is a comprehensive discussion that identifies several generically different ways to make the case.) Locality affirms that the real state of a system is not affected by distant measurements. Since the real state determines which quantities are definite (i.e., have assigned values), the set of definite quantities is also not affected by distant measurements. So if by measuring a distant partner we can determine that a certain quantity is definite, then that quantity must have been definite all along. As we have seen, the  Criterion of Reality  implies that a quantity is definite if the state of the system is an eigenstate for that quantity. In the case of the strict correlations of EPR, measuring one system triggers a reduction of the joint state that results in an eigenstate for the distant partner. Hence any quantity with that eigenstate is definite. For example, since measuring the momentum of Albert’s system results in a momentum eigenstate for Niels’, the momentum of Niels’ system is definite. Likewise for the position of Niels’ system. Given separability, the combination of locality and the Criterion establish a quite general lemma; namely, when quantities on separated systems have strictly correlated values, those quantities are definite. Thus the strict correlations between Niels’ system and Albert’s in the EPR situation guarantee that both position and momentum are definite; i. e., that each system has definite position and momentum simultaneously.