@article{MZM_1991_50_1_a3,
     author = {K. Yu. Gorbunov},
     title = {There does not exist an enumerable family of context-free grammars that generates the class of single-valued languages},
     journal = {Matemati\v{c}eskie zametki},
     pages = {34--40},
     publisher = {mathdoc},
     volume = {50},
     number = {1},
     year = {1991},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1991_50_1_a3/}
}