Proofs of the Kochen-Specker theorem based on two qubits

The observables for a pair of qubits yield a system of 60 rays and 105 bases in a complex Hilbert space of four dimensions that contains over a hundred million parity proofs of the Kochen-Specker theorem. An overview of these proofs is given and they are compared with those in other 4-d systems, such as the 600-cell. The significance of the results is discussed.