@article{DAN_1974_217_5_a6,
     author = {A. N. Maslov},
     title = {The hierarchy of indexed languages of an arbitrary level},
     journal = {Doklady Akademii Nauk},
     pages = {1013--1016},
     year = {1974},
     volume = {217},
     number = {5},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1974_217_5_a6/}
}