In Bell-type experiments, the correlations of two distant particles are indicating if these distant objects are entangled or not. Two parties A and B take independent measurement a and b of presumably entangled objects originating from a source S. Each measurement can have outcome D+ or D-. A Coincidence measurement (CM) allows to determine if the experimental results can be explained by classical (hidden variable) theories. Thus if the particles are entangled, no classical correlations (and thus no cheating) can explain the outcome of the measurements and it is possible to generate truly random numbers.
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