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doi:10.1002/j.1538-7305.1948.tb01338.x
https://sci-hub.ru/10.1002/j.1538-7305.1948.tb01338.x
https://en.wikipedia.org/wiki/Shannon%27s_source_coding_theo...
https://faculty.uml.edu/jweitzen/16.548/classnotes/Theory%20...