This looks like some kind of variant of Bell's Theorem. I've not seen it before, but it reminds me of the GHZ inequality [0] [[EDIT - actually I take that back

This looks like some kind of variant of Bell's Theorem. I've not seen it before, but it reminds me of the GHZ inequality [0] [[EDIT - actually I take that back. The GHZ inequality refers to three systems whereas your link refers to three measurement choices]]. I don't think your link gives a derivation of the quantum correlations beyond "Quantum physics says that half the time they should get a match". [0] https://en.wikipedia.org/wiki/Bell%27s_theorem#GHZ%E2%80%93Mermin_(1990) https://en.wikipedia.org/wiki/Bell%27s_theorem#GHZ%E2%80%93M...