It is shown that the 33 complex rays in three dimensions used by Penrose to prove the Bell-Kochen-Specker theorem have the same orthogonality relations as the 33 real rays of Peres, and therefore provide an isomorphic proof of the theorem. It is further shown that the Peres and Penrose rays are just two members of a continuous three-parameter family of unitarily inequivalent rays that prove the theorem.
Gould, E., Aravind, P.K. Isomorphism between the Peres and Penrose Proofs of the BKS Theorem in Three Dimensions. Found Phys 40, 1096–1101 (2010). https://doi.org/10.1007/s10701-010-9434-2
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