“ The necessary knowledge is that of what to observe. ”
 Edgar Allan Poe, The Murders in the Rue Morgue (1841). copy citation

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“He makes, in silence, a host of observations and inferences. So, perhaps, do his companions; and the difference in the extent of the information obtained, lies not so much in the validity of the inference as in the quality of the observation. The necessary knowledge is that of what to observe. Our player confines himself not at all; nor, because the game is the object, does he reject deductions from things external to the game. He examines the countenance of his partner, comparing it carefully with that of each of his opponents.” source

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