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A gedanken experiment discovered by Lucien Hardy is translated into a very direct black-box gedanken demonstration of quantum nonlocality with red and green lights, using only two far apart detectors each of which operates in only two modes. The quantum mechanical underpinnings of the gedanken demonstration are quite simple. (This paper provides a text for the Klopsteg Memorial Lecture to the American Association of Physics Teachers at Notre Dame University, August 11, 1994.)
N. David Mermin (Sat,) studied this question.