@article{MAT_1959_3_5_a6,
     author = {D. Blackwell},
     title = {The entropy of functions of finite-state {Markov} chains},
     journal = {Matematika},
     pages = {143--150},
     year = {1959},
     volume = {3},
     number = {5},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MAT_1959_3_5_a6/}
}